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• 1.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Moscow, Russia. Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Russia. Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Tomsk, Russia; Department of Physics and Engineering, Tomsk State University, Tomsk, Russia.
Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics2013Ingår i: TMS2013 Supplemental Proceedings, John Wiley & Sons, 2013, s. 617-626Kapitel i bok, del av antologi (Refereegranskat)

Ab initio electronic structure theory is known as a useful tool for prediction of materials properties. However, majority of simulations still deal with calculations in the framework of density functional theory with local or semi-local functionals carried out at zero temperature. We present new methodological solution.s, which go beyond this approach and explicitly take finite temperature, magnetic, and many-body effects into account. Considering Ti-based alloys, we discuss !imitations of the quasiharmonic approximation for the treatment of lattice vibrations, and present an accurate and easily extendable method to calculate free ,energies of strongly anharmonic solids. We underline the necessity to going beyond the state-of-the-art techniques for the determination of effective cluster interactions in systems exhibiting mctal-to-insulator transition, and describe a unified cluster expansion approach developed for this class of materials. Finally, we outline a first-principles method, disordered local moments molecular dynamics, for calculations of thermodynamic properties of magnetic alloys, like Cr1-x,.AlxN, in their high-temperature paramagnetic state. Our results unambiguously demonstrate importance of finite temperature effects in theoretical calculations ofthermodynamic properties ofmaterials.

• 2.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany. Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
Semi-Empirical Force-Field Model For The Ti1-XAlXN (0 ≤ x ≤ 1) System2019Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 2, artikel-id 215Artikel i tidskrift (Refereegranskat)

We present a modified embedded atom method (MEAM) semi-empirical force-field model for the Ti1-xAlxN (0 x 1) alloy system. The MEAM parameters, determined via an adaptive simulated-annealing (ASA) minimization scheme, optimize the models predictions with respect to 0 K equilibrium volumes, elastic constants, cohesive energies, enthalpies of mixing, and point-defect formation energies, for a set of approximate to 40 elemental, binary, and ternary Ti-Al-N structures and configurations. Subsequently, the reliability of the model is thoroughly verified against known finite-temperature thermodynamic and kinetic properties of key binary Ti-N and Al-N phases, as well as properties of Ti1-xAlxN (0 amp;lt; x amp;lt; 1) alloys. The successful outcome of the validation underscores the transferability of our model, opening the way for large-scale molecular dynamics simulations of, e.g., phase evolution, interfacial processes, and mechanical response in Ti-Al-N-based alloys, superlattices, and nanostructures.

• 3.
Univ West, Sweden.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Univ West, Sweden. Univ West, Sweden. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Univ West, Sweden.
Microstructural influence on fatigue crack propagation during high cycle fatigue testing of additively manufactured Alloy 7182019Ingår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 149, s. 82-94Artikel i tidskrift (Refereegranskat)

A study of the microstructure of additively manufactured Alloy 718 was performed in order to better understand the parameters that have an influence on the fatigue properties of the material. The specimens were manufactured using two powder bed fusion techniques - Electron Beam Melting (EBM) and Selective Laser Melting (SLM). Four point bending fatigue tests were performed at room temperature with a stress ratio of R = 0.1 and 20 Hz frequency, on material that was either in hot isostatically pressed (HIP) and solution treated and aged (STA) condition or in STA condition without a prior HIP treatment. The grains in the SLM material in the HIP + STA condition have grown considerably both in the hatch and the contour regions; EBM material, in contrast, shows grain growth only in the contour region. Fractographic analysis of the specimens in HIP + STA condition showed a faceted appearance while the specimens in STA condition showed a more planar crack appearance. The crack propagation occurred in a transgranular mode and it was found that precipitates such as NbC, TiN or 8-phase, when present, did not affect the crack path. The areas with larger grains corresponded to the faceted appearance of the fracture surface. This could be attributed to the plastic zone ahead of the crack tip being confined within one grain, in case of the larger grains, which promotes single shear crack growth mode.

• 4.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanostrukturerade material. Linköpings universitet, Tekniska fakulteten. Department of Material Science, Saarland University, Saarbrücken, Germany.
Eutectic Modification of Al-Si casting alloys2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

Aluminum alloys with silicon as the major alloying element are the most widely used aluminum casting alloys. The eutectic phase in these alloys is formed by hard and brittle silicon plates in an aluminum matrix. Such silicon plates can act as crack propagation paths deteriorating the toughness of the material. To enhance ductility, silicon can be modified to a coral-like microstructure by addition of a modifying agent. Amongst the elements proposed as modifiers, only strontium, sodium and europium induce a plate-tocoral transition, while others such as ytterbium, only refine the silicon plates. The exact mechanism for the remarkable plate-to-coral change, and the reason why certain elements only refine the structure, is still not completely understood.

In this investigation, atom probe tomography and transmission electron microscopy were used to analyze and compare the crystal structure and the distribution of solute atoms in silicon at the atomic level. An unmodified alloy and alloys modified by strontium, sodium, europium and ytterbium were studied. Elements inducing silicon plate-to-coral transition were found to contain nanometer sized clusters at the defects in silicon with stoichiometries corresponding to compounds formed at the ternary eutectic reaction of each system. In contrast, the addition of ytterbium, that only refines the silicon plates, is unable to form clusters in silicon. We propose that the formation of ternary compound clusters AlSiNa, Al2Si2Sr and Al2Si2Eu at the silicon / liquid interface during solidification restrict silicon growth. The formation of clusters on silicon facets create growth steps and increase growth direction diversity. The incorporation of clusters in silicon explains the high density of crystallographic defects and the structural modification from plates to corals.

The parallel lattice plane-normals 011Si // 0001Al2Si2Eu, 011Si // 6$\tiny\overline{7}$10Al2Si2Eu and 111Si // 6$\tiny\overline{7}$10Al2Si2Eu were found between Al2Si2Eu and silicon, and absent between Al2Si2Yb and silicon. We propose a favorable heterogeneous formation of Al2Si2Eu on silicon. The misfit between 011Si and 0002Al2Si2X interplanar spacings shows a consistent trend with the potency of modification for several elements such as strontium, sodium, europium, calcium, barium, ytterbium and yttrium.

1. Comparison of segregations formed in unmodified and Sr-modified Al-Si alloys studied by atom probe tomography and transmission electron microscopy
Öppna denna publikation i ny flik eller fönster >>Comparison of segregations formed in unmodified and Sr-modified Al-Si alloys studied by atom probe tomography and transmission electron microscopy
2014 (Engelska)Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 611, s. 410-421Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The mechanical properties of Al-7 wt.% Si can be enhanced by structural modifications of its eutectic phase. Addition of low concentrations of certain elements, in this case 150 wt-ppm Sr, is enough to cause a transition from a coarse plate-like Si structure to a finer coralline one. To fully understand the operating mechanism of this modification, the composition of the eutectic Si phase in unmodified and Sr-modified alloys was analysed and compared by atom probe tomography and (scanning) transmission electron microscopy. The unmodified alloy showed nanometre sized Al-segregations decorating defects, while the Sr-modified sample presented three types of Al-Sr segregations: (1) rod-like segregations that promote smoothening of the Al-Si boundaries in the eutectic phase, (2) particle-like segregations comparable to the ones seen in the unmodified alloy, and (3) planar segregations favouring the formation of twin boundaries. Al and Sr solubilities in Si after solidification were determined to be 430 +/- 160 at-ppm and 40 +/- 10 at-ppm, respectively. Sr predominantly segregates to the Si phase confirming its importance in the modification of the eutectic growth.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2014
##### Nyckelord
Aluminium-silicon alloys; Strontium modification; Atom probe tomography; Transmission electron microscopy; Microstructure
Fysik
##### Identifikatorer
urn:nbn:se:liu:diva-109356 (URN)10.1016/j.jallcom.2014.05.121 (DOI)000338932400064 ()
2. Cluster formation at the Si/liquid interface in Sr and Na modified Al-Si alloys
Öppna denna publikation i ny flik eller fönster >>Cluster formation at the Si/liquid interface in Sr and Na modified Al-Si alloys
2016 (Engelska)Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 117, s. 16-19Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Atom probe tomography was used to compare Na and Sr modified Al-Si hypoeutectic alloys. Both Na and Sr promote the formation of nanometre-sized clusters in the Si eutectic phase. Compositional analyses of the clusters show an Al:Sr ratio of 2.92 +/- 0.46 and an Al:Na ratio of 1.07 +/- 0.23. It is proposed that SrAl2Si2 and NaAlSi clusters are formed at the Si/liquid interface and take part in the modification process by altering the eutectic Si growth.

##### Ort, förlag, år, upplaga, sidor
PERGAMON-ELSEVIER SCIENCE LTD, 2016
##### Nyckelord
Eutectic solidification; Atom probe tomography; Aluminium alloys; Eutectic modification; Transmission electron microscopy
Fysik
##### Identifikatorer
urn:nbn:se:liu:diva-127548 (URN)10.1016/j.scriptamat.2016.02.018 (DOI)000373547500004 ()
##### Anmärkning

Funding Agencies|German Federal Ministry of Economics and Technology [AiF 17204 N]; European Regional Development Fund (AME-Lab) [C/4-EFRE-13/2009/Br]; German Research Foundation (DFG); Federal State Government of Saarland [INST 256/298-1 FUGG]; Erasmus Mundus Doctoral Programme DocMASE of the European Commission [FPA 2011-0020]; VINNOVA Strategic Faculty Grant VINNMER Marie Curie Chair [2011-03464]; Major International (Regional) Joint Research Project from China [51420105005]

3. Eutectic modification by ternary compound cluster formation in Al-Si alloys
Öppna denna publikation i ny flik eller fönster >>Eutectic modification by ternary compound cluster formation in Al-Si alloys
2019 (Engelska)Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 5506Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Al-alloys with Si as the main alloying element constitute the vast majority of Al castings used commercially today. The eutectic Si microstructure in these alloys can be modified from plate-like to coral-like by the addition of a small amount of a third element to improve ductility and toughness. In this investigation the effects of Eu and Yb are studied and their influence on the microstructure is compared to further understand this modification. The two elements impact the alloy differently, where Eu modifies Si into a coral-like structure while Yb does not. Atom probe tomography shows that Eu is present within the Si phase in the form of ternary compound Al2Si2Eu clusters, while Yb is absent in the Si phase. This indicates that the presence of ternary compound clusters within Si is a necessary condition for the formation of a coral-like structure. A crystallographic orientation relationship between Si and the Al2Si2Eu phase was found, where the following plane normals are parallel: 011(Si) //0001(Al2Si2Eu), 111(Si)//6 (7) over bar 10(Al2Si2Eu) and 011(Si)//6 (7) over bar 10(Al2Si2Eu). No crystallographic relationship was found between Si and Al2Si2Yb. The heterogeneous formation of coherent Al2Si2Eu clusters inside the Si-phase is suggested to trigger the modification of the microstructure.

##### Ort, förlag, år, upplaga, sidor
NATURE PUBLISHING GROUP, 2019
##### Nationell ämneskategori
Metallurgi och metalliska material
##### Identifikatorer
urn:nbn:se:liu:diva-156563 (URN)10.1038/s41598-019-41919-2 (DOI)000462990000048 ()30940873 (PubMedID)
##### Anmärkning

Funding Agencies|European Regional Development Fund (ERDF); DFG; Federal State Government of Saarland [INST 256/298-1 FUGG]; Erasmus Mundus Programme of the European Commission within the Doctoral Programme DocMASE; Major International (Regional) Joint Research Project from China [51420105005]; Overseas, Hong Kong, Macao Scholars Cooperative Research Fund from China [51728101]

4. Nucleation and Growth of Eutectic Si in Al-Si Alloys with Na Addition
Öppna denna publikation i ny flik eller fönster >>Nucleation and Growth of Eutectic Si in Al-Si Alloys with Na Addition
2015 (Engelska)Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 46, nr 3, s. 1300-1311Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Al-5 wt pct Si-based alloys with Na additions (19 and 160 ppm) have been produced by controlled sand casting and melt spinning. Entrained droplet technique and differential scanning calorimetry were employed to investigate the nucleation behavior of eutectic Si. High-resolution transmission electron microscopy and atom probe tomography were used to investigate the distribution of Na atoms within eutectic Si and at the interfaces between eutectic Si and eutectic Al. It was found that (i) only 19 ppm Na addition results into a high undercooling (49 K (49 °C)) of the entrained eutectic droplet. However, further increasing Na addition up to 160 ppm exerts no positive effect on the nucleation of eutectic Si, instead a decreased undercooling (29 K (29 °C)) was observed. (ii) Na addition suppresses the growth of eutectic Si due to the Na segregation at the interface between eutectic Si and eutectic Al, and (iii) Na addition promotes significant multiple Si twins, which can be attributed to the proposed adsorption of Na atoms at the intersection of Si twins and along the 〈112〉Si growth direction of Si. The present investigation demonstrates, for the first time, a direct observation on the distribution of Na atoms within eutectic Si and thereby provides strong experimental supports to the well-accepted impurity-induced twinning growth mechanism and poisoning of the twin plane re-entrant edge growth mechanism.

##### Identifikatorer
urn:nbn:se:liu:diva-160234 (URN)10.1007/s11661-014-2702-6 (DOI)
5. Phase Selective Sample Preparation of Al-Si alloys for Atom Probe Tomography
Öppna denna publikation i ny flik eller fönster >>Phase Selective Sample Preparation of Al-Si alloys for Atom Probe Tomography
2019 (Engelska)Ingår i: Praktische metallographie, ISSN 0032-678X, E-ISSN 2195-8599, Vol. 56, nr 2, s. 76-90Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

We present how the conventional focused ion beam (FIB) lift-out method can be modified to obtain phase selective specimens for atom probe tomography (APT). The modified method combines selective deep etching with site-specific lift-out using a micromanipulator in a FIB/SEM workstation. This method is used for phase-selective sample preparation in alloys with complex microstructures such as the coral- and plate-like silicon structures in the eutectic phase of Al-Si castings. The method proves to be both, practical and robust, with a high success rate of high-quality phase-specific APT specimens.

##### Ort, förlag, år, upplaga, sidor
CARL HANSER VERLAG, 2019
##### Nationell ämneskategori
Analytisk kemi
##### Identifikatorer
urn:nbn:se:liu:diva-154847 (URN)10.3139/147.110557 (DOI)000458507500002 ()
##### Anmärkning

Funding Agencies|EU; DFG; Federal State Government of Saarland [INST 256/298-1 FUGG]; Erasmus Mundus Programme of the European Commission within the Doctoral Programme DocMASE

• 5.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanostrukturerade material. Linköpings universitet, Tekniska fakulteten. Saarland Univ, Germany.
Saarland Univ, Germany. Saarland Univ, Germany. Univ Lorraine, France. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Leoben, Austria. Univ Leoben, Austria. Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanostrukturerade material. Linköpings universitet, Tekniska fakulteten. Saarland Univ, Germany.
Eutectic modification by ternary compound cluster formation in Al-Si alloys2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 5506Artikel i tidskrift (Refereegranskat)

Al-alloys with Si as the main alloying element constitute the vast majority of Al castings used commercially today. The eutectic Si microstructure in these alloys can be modified from plate-like to coral-like by the addition of a small amount of a third element to improve ductility and toughness. In this investigation the effects of Eu and Yb are studied and their influence on the microstructure is compared to further understand this modification. The two elements impact the alloy differently, where Eu modifies Si into a coral-like structure while Yb does not. Atom probe tomography shows that Eu is present within the Si phase in the form of ternary compound Al2Si2Eu clusters, while Yb is absent in the Si phase. This indicates that the presence of ternary compound clusters within Si is a necessary condition for the formation of a coral-like structure. A crystallographic orientation relationship between Si and the Al2Si2Eu phase was found, where the following plane normals are parallel: 011(Si) //0001(Al2Si2Eu), 111(Si)//6 (7) over bar 10(Al2Si2Eu) and 011(Si)//6 (7) over bar 10(Al2Si2Eu). No crystallographic relationship was found between Si and Al2Si2Yb. The heterogeneous formation of coherent Al2Si2Eu clusters inside the Si-phase is suggested to trigger the modification of the microstructure.

• 6.
Sandvik Int Trading, Peoples R China.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Sandvik Mat Technology, Sweden. Sandvik Mat Technology, Sweden. Sandvik Int Trading, Peoples R China.
Investigation of cold-forming properties of Sanicro 25-a potential candidate for superheater and reheaters in high efficiency A-USC fossil power plants2017Ingår i: PROCEEDINGS OF THE ASME POWER CONFERENCE JOINT WITH ICOPE-17, 2017, VOL 1, AMER SOC MECHANICAL ENGINEERS , 2017, artikel-id UNSP V001T01A008Konferensbidrag (Refereegranskat)

Sanicro 25 material is approved for use in pressure vessels and boilers according AMSE code case 2752, 2753 and VdTuN blatt 555. It shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than any other austenitic stainless steels available today. It is a candidate material for superheater and reheaters, enabling higher steam parameters of up to about 650 degrees C steam (ie about max 700 degrees C metal) without the need for expensive nickel based alloys. The effect of cold-forming on time and temperature-dependent deformation and strength behavior has been examined in a comprehensive study. The objective was to determine the maximum allowable degree of cold-forming to be used without additional heat treatment. The findings of these investigations indicate that the maximum allowed cold deformation could be possible to increase from todays maximum 20 % (VdTuV 555), 15 % (540-675 degrees C) and 10 % (higher than 675 degrees C) respectively (ASME 2011a Sect I PG19). A solution annealing after the cold bending will recover creep ductility but will also at the same time increase manufacturing costs. Higher allowed degree of cold-forming without the need for post bend heat treatments, would allow for more narrow bending radii and thereby a more compact construction that would result in a significant decrease in production costs. This paper presents the findings in the mentioned study and is to be a background for possible coming discussions with involved entities on a revision of the max allowed deformation of this material without the need for solution annealing.

• 7.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial.
Microstructural inhomogeneity and anisotropicproperties in IN-718 structures fabricated byElectron Beam Melting: Mikrostrukturell inhomogenitet och anisotropa egenskaper i strukturerav IN-718 tillverkade genom Electron Beam Melting2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Additive Manufacturing, or 3D printing, provides an opportunity to manufacture advanced 3D geometrieswith little material waste and reduced need for tooling compared to conventional methods. There are,however, challenges remaining regarding anisotropy in the mechanical properties of built components.

The aim of this project is to investigate the anisotropy of additive manufactured material and the effect ofdifferent build directions. The material used is Inconel 718, which was manufactured by Electron BeamMelting as vertical and horizontal rods. The tests performed are microstructural investigations about thegrains, precipitates and porosities, but also include hardness testing and tensile testing. The material istested in its as-built state.

The results show that the material consist of an anisotropic microstructure with elongated grains in thebuild direction. The build height has a bigger influence on the properties of the material than the builddirection for the specimens. The top pieces are consistently different from the others and are the leasthomogeneous. The microstructure consists of large quantities of delta-phase, and solidification pores arefound throughout the material. The hardness of the material differs from 324 HV to 408 HV depending onthe part of the build. The tensile testing shows that the vertically built specimens have a higher yieldstrength and ultimate tensile strength while the horizontally built specimens have a greater ductility.

• 8.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
On High-Temperature Behaviours of Heat Resistant Austenitic Alloys2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

Advanced heat resistant materials are important to achieve the transition to long term sustainable power generation. The global increase in energy consumption and the global warming from greenhouse gas emissions create the need for more sustainable power generation processes. Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO2. Biomass offers no net contribution of CO2 to the atmosphere. To obtain greater efficiency of power plants, one option is to increase the temperature and the pressure in the boiler section of the power plant. This requires improved material properties, such as higher yield strength, creep strength and high-temperature corrosion resistance, as well as structural integrity and safety.

Today, some austenitic stainless steels are design to withstand temperatures up to 650 °C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of future operation conditions in biomass-red power plants is not yet fully understood.

This thesis presents research on the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture, and the influence of high-temperature environment and cyclic operation conditions on the material behaviour. Mechanical and thermal testing have been performed followed by subsequent studies of the microstructure, using scanning electron microscopy, to investigate the material behaviours.

Results shows that long term ageing at high temperatures leads to the precipitation of intermetallic phases. These intermetallic phases are brittle at room temperature and become detrimental for the impact toughness of some of the austenitic stainless steels. During slow strain rate tensile deformation at elevated temperature time dependent deformation and recovery mechanisms are pronounced. The creep-fatigue interaction behaviour of an austenitic stainless steel show that dwell time gives shorter life at a lower strain range, but has none or small effect on the life at a higher strain range.

Finally, this research results in an increased knowledge of the structural, mechanical and chemical behaviour as well as a deeper understanding of the deformation, damage and fracture mechanisms that occur in heat resistant austenitic alloys at high-temperature environments. It is believed that in the long term, this can contribute to material development achieving the transition to more sustainable power generation in biomass-red power plants.

1. Long Term High-Temperature Environmental Effect on Impact Toughness in Austenitic Alloys
Öppna denna publikation i ny flik eller fönster >>Long Term High-Temperature Environmental Effect on Impact Toughness in Austenitic Alloys
2015 (Engelska)Ingår i: / [ed] Key Engineering Materials Vol 627 (2015),pp 205-208., 2015, s. 205-308Konferensbidrag, Publicerat paper (Refereegranskat)
##### Serie
KEY ENGINEERING MATERIALS, ISSN 1662-9795 ; 627
##### Nyckelord
high-temperature environment, precipitation, impact toughness, austenitic stainless steel, nickel-base alloy
##### Nationell ämneskategori
Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-109512 (URN)10.4028/www.scientific.net/KEM.627.205 (DOI)
##### Konferens
13th International Conference on Fracture and Damage Mechanics, Azorerna, 23-25 September 2014
2. Damage and Fracture Behaviours in Aged Austentic Materials During High-Temperature Slow Strain Rate Testing
Öppna denna publikation i ny flik eller fönster >>Damage and Fracture Behaviours in Aged Austentic Materials During High-Temperature Slow Strain Rate Testing
2014 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

Biomass power plants with high efficiency are desired as a renewable energy resource. High efficiency can be obtained by increasing temperature and pressure. An upgrade of the material performance to high temperature material is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. In this study, the material’s high-temperature behaviours of AISI 304 and Alloy617 under slow deformation rate are evaluated using high-temperature long-term aged specimens subjected to slow strain rate tensile testing (SSRT) with strain rates down to 10-6/s at 700°C. Both materials show decreasing stress levels and elongation to fracture when tensile deformed using low strain rate and elevated temperature. At high-temperature and low strain rates cracking in grain boundaries due to larger precipitates formed during deformation is the most common fracture mechanism.

##### Ort, förlag, år, upplaga, sidor
Trans Tech Publications Inc., 2014
##### Serie
Key Engineering Materials, ISSN 1662-9795
##### Nyckelord
High-temperature, ageing, slow strain rate, biomass power plant, austenitic stainless steel, nickel base alloy and dynamic strain ageing
##### Nationell ämneskategori
Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-96028 (URN)10.4028/www.scientific.net/KEM.592-593.590 (DOI)000336694400133 ()
##### Konferens
MSMF7 Materials Structure & Micromechanics of Fracture , July 13, Brno, Czech Republic
3. Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM
Öppna denna publikation i ny flik eller fönster >>Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM
2014 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

In this study an advanced method for investigation of the microstructure such as electron backscatter diffraction (EBSD) together with in-situ tensile test in a scanning electron microscope (SEM) has been used at room temperature and 300°C. EBSD analyses provide information about crystallographic orientation in the microstructure and dislocation structures caused by deformation. The in-situ tensile tests enabled the same area to be investigated at different strain levels. For the same macroscopic strain values a lower average misorientation in individual grains at elevated temperature indicates that less residual strain at grain level are developed compared to room temperature. For both temperatures, while large scatters in grain average misorientation are observed for grains of similar size, there seems to be a tendency showing that larger grains may accumulate somewhat more strains.

##### Ort, förlag, år, upplaga, sidor
Trans Tech Publications Inc., 2014
##### Serie
Key Engineering Materials, ISSN 1662-9795
##### Nyckelord
Austenitic stainless steel, electron backscatter diffraction, in-situ tensile test, Schmid factor, grain wsize and slip system
##### Nationell ämneskategori
Teknik och teknologier Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-97015 (URN)10.4028/www.scientific.net/KEM.592-593.497 (DOI)000336694400111 ()
##### Konferens
MSMF7 Materials Structure & Micromechanics of Fracture, July 1-3, Brno, Czech Republic
4. Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures
Öppna denna publikation i ny flik eller fönster >>Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures
2014 (Engelska)Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 783-786, s. 1182-1187Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Nickel-base alloys due to their high performances have been widely used in biomass and coal fired power plants. They can undertake plastic deformation with different strain rates such as those typically seen during creep and fatigue at elevated temperatures. In this study, the mechanical behaviours of Alloy 617 with strain rates from 10-2/s down to 10-6/s at temperatures of 650°C and 700°C have been studied using tensile tests. Furthermore, the microstructures have been investigated using electron backscatter detection and electron channeling contrast imaging. At relatively high strain rate, the alloy shows higher fracture strains at these temperatures. The microstructure investigation shows that it is caused by twinning induced plasticity due to DSA. The fracture strain reaches the highest value at a strain rate of 10-4/s and then it decreases  dramatically. At strain rate of 10-6/s, the fracture strain at high temperature is now smaller than that at room temperature, and the strength also decreases with further decreasing strain rate. Dynamic recrystallization can also be observed usually combined with crack initiation and propagation. This is a new type of observation and the mechanisms involved are discussed.

##### Nyckelord
Nickel-base superalloy, twinning, Dynamic strain ageing, elevated temperature
##### Nationell ämneskategori
Teknik och teknologier Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-98241 (URN)10.4028/www.scientific.net/MSF.783-786.1182 (DOI)
##### Konferens
THERMEC '2013, International Conference on Processing & Manufacturing of Advanced Materials. Processing, Fabrication, Properties, Applications. December 2-6, Las Vegas, USA
5. Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature
Öppna denna publikation i ny flik eller fönster >>Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature
2014 (Engelska)Ingår i: Theoretical and Applied Mechanics Letters, ISSN 2095-0349, Vol. 4, nr 041004Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel (AISI 316L) and one nickel-base alloy (Alloy 617) have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromechanisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650°C.

##### Ort, förlag, år, upplaga, sidor
American Institute of Physics (AIP), 2014
##### Nyckelord
dynamic strain ageing, slow strain rate tensile testing, fracture, damage
##### Nationell ämneskategori
Materialteknik Teknik och teknologier
##### Identifikatorer
urn:nbn:se:liu:diva-109511 (URN)10.1063/2.1404104 (DOI)
6. Characterization of austenitic stainless steels deformed at elevated temperature
Öppna denna publikation i ny flik eller fönster >>Characterization of austenitic stainless steels deformed at elevated temperature
2017 (Engelska)Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, nr 10, s. 4525-4538Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Highly alloyed austenitic stainless steels are promising candidates to replace more expansive nickel-based alloys within the energy-producing industry. The present study investigates the deformation mechanisms by microstructural characterisation, mechanical properties and stress-strain response of three commercial austenitic stainless steels and two commercial nickel-based alloys using uniaxial tensile tests at elevated temperatures from 400 C up to 700 C. The materials showed different influence of temperature on ductility, where the ductility at elevated temperatures increased with increasing nickel and solid solution hardening element content. The investigated materials showed planar dislocation driven deformation at elevated temperature. Scanning electron microscopy showed that deformation twins were an active deformation mechanism in austenitic stainless steels during tensile deformation at elevated temperatures up to 700 C.

##### Ort, förlag, år, upplaga, sidor
Springer-Verlag New York, 2017
##### Nyckelord
Austenitic stainless steel, Nickel-based alloy, Microstructural characterization, Deformation twinning, Stress-strain response
##### Nationell ämneskategori
Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-122942 (URN)10.1007/s11661-017-4212-9 (DOI)000408884300012 ()
##### Anmärkning

Previous status of this publication was manuscript

Funding agencies: AB Sandvik Materials Technology in Sweden; Swedish National Energy Administration through the Research Consortium of Materials Technology for Thermal Energy Processes [KME-701]; AFM Strategic Faculty Grant SFO-MAT-LiU at Linkoping University [2009-00971]

7. Characterisation of creep deformation during slow strain rate tensile testing
Öppna denna publikation i ny flik eller fönster >>Characterisation of creep deformation during slow strain rate tensile testing
2015 (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
##### Abstract [en]

The strain-rate dependent deformation of the superalloy Haynes 282 during slow strain-rate tensile testing (SSRT) at 700 C has been investigated. The stress-strain response is remarkably well described by a simple constitutive model over a wide range of different strain-rates. The microstructure development is characterised and related to the influence of both strainrate dependent and independent deformation. Damage and cracking similar to what has been observed previously during conventional creep testing of Haynes 282 was found and explained. The model and the microstructure investigations show that the deformation and damage mechanisms during SSRT are essentially the same as under creep.

##### Nyckelord
Slow strain-rate tensile testing, Creep, Norton equation, Constitutive modelling, Cavity
##### Nationell ämneskategori
Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-122943 (URN)
8. Creep and Fatigue Interaction Behavior in Sanicro 25 Heat Resistant Austenitic Stainless Steel
Öppna denna publikation i ny flik eller fönster >>Creep and Fatigue Interaction Behavior in Sanicro 25 Heat Resistant Austenitic Stainless Steel
2016 (Engelska)Ingår i: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 69, nr 2, s. 337-342Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Sanicro 25 is a newly developed advanced high strength heat resistant austenitic stainless steel. The material shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than other austenitic stainless steels available today. It is thus an excellent candidate for superheaters and reheaters for advanced ultra-super critical power plants with efficiency higher than 50 %. This paper provides a study on the creep–fatigue interaction behavior of Sanicro 25 at 700 °C. Two strain ranges, 1 and 2 %, and two dwell times, 10 and 30 min, were used. The influences of dwell time on the cyclic deformation behavior and life has been evaluated. Due to stress relaxation the dwell time causes a larger plastic strain range compared to the tests without dwell time. The results also show that the dwell time leads to a shorter fatigue life for the lower strain range, but has no or small effect on the life for the higher strain range. Fracture investigations show that dwell times result in more intergranular cracking. With the use of the electron channeling contrast imaging technique, the influences of dwell time on the cyclic plastic deformation, precipitation behavior, recovery phenomena and local plasticity exhaustion have also been studied.

##### Ort, förlag, år, upplaga, sidor
Springer, 2016
##### Nyckelord
Sanicro 25, advanced ultra-super critical power plant, creep, low cycle fatigue, cyclic plastic deformation
##### Nationell ämneskategori
Metallurgi och metalliska material
##### Identifikatorer
urn:nbn:se:liu:diva-123646 (URN)10.1007/s12666-015-0806-3 (DOI)000368032700027 ()
##### Konferens
7th International Conference on Creep, 19-22 January 2016, IGCAR, Kalpakkam, India
##### Anmärkning

At the time for thesis presentation publication was in status: Manuscript

Funding agencies: AB Sandvik Materials Technology in Sweden; Swedish National Energy Administration through the Research Consortium of Materials Technology for Thermal Energy Processes [KME-701]; AFM Strategic Faculty Grant SFO-MAT-LiU at Linkoping University [2009-00971]

9. Surface Phase Transformation in Austenitic Stainless Steel Induced by Cyclic Oxidation in Humidified Air
Öppna denna publikation i ny flik eller fönster >>Surface Phase Transformation in Austenitic Stainless Steel Induced by Cyclic Oxidation in Humidified Air
2015 (Engelska)Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 100, s. 524-534Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The formation of α’ martensite at the surface of an AISI 304 stainless steel subjected to cyclic heating in humidified air is reported. The α’ martensite formed during the cooling part of the cyclic tests due to local depletion of Cr and Mn and transformed back to austenite when the temperature again rose to 650 °C. The size of the α’ martensite region increased with increasing number of cycles. Thermodynamical simulations were used as basis for discussing the formation of α’ martensite. The effect of the α’ martensite on corrosion is also discussed.

##### Ort, förlag, år, upplaga, sidor
Pergamon Press, 2015
##### Nyckelord
Stainless steel, thermal cycling, SEM, oxidation, high temperature corrosion
##### Nationell ämneskategori
Metallurgi och metalliska material
##### Identifikatorer
urn:nbn:se:liu:diva-122008 (URN)10.1016/j.corsci.2015.08.030 (DOI)000363070100049 ()
##### Anmärkning

Funding agencies: AB Sandvik Materials Technology in Sweden; Swedish National Energy Administration through the Research Consortium of Materials Technology for Thermal Energy Processes [KME-701]; Agora Materiae and AFM Strategic Faculty Grant SFO-MAT-LiU at Linkoping Unive

• 9.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Sandvik Materials Technology,Sandviken, Sweden. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
Creep and Fatigue Interaction Behavior in Sanicro 25 Heat Resistant Austenitic Stainless Steel2016Ingår i: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 69, nr 2, s. 337-342Artikel i tidskrift (Refereegranskat)

Sanicro 25 is a newly developed advanced high strength heat resistant austenitic stainless steel. The material shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than other austenitic stainless steels available today. It is thus an excellent candidate for superheaters and reheaters for advanced ultra-super critical power plants with efficiency higher than 50 %. This paper provides a study on the creep–fatigue interaction behavior of Sanicro 25 at 700 °C. Two strain ranges, 1 and 2 %, and two dwell times, 10 and 30 min, were used. The influences of dwell time on the cyclic deformation behavior and life has been evaluated. Due to stress relaxation the dwell time causes a larger plastic strain range compared to the tests without dwell time. The results also show that the dwell time leads to a shorter fatigue life for the lower strain range, but has no or small effect on the life for the higher strain range. Fracture investigations show that dwell times result in more intergranular cracking. With the use of the electron channeling contrast imaging technique, the influences of dwell time on the cyclic plastic deformation, precipitation behavior, recovery phenomena and local plasticity exhaustion have also been studied.

• 10.
Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial.
Siemens AG, Huttenstr. 12, 10553 Berlin, Germany. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Sandviken, Sweden. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
Surface Phase Transformation in Austenitic Stainless Steel Induced by Cyclic Oxidation in Humidified Air2015Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 100, s. 524-534Artikel i tidskrift (Refereegranskat)

The formation of α’ martensite at the surface of an AISI 304 stainless steel subjected to cyclic heating in humidified air is reported. The α’ martensite formed during the cooling part of the cyclic tests due to local depletion of Cr and Mn and transformed back to austenite when the temperature again rose to 650 °C. The size of the α’ martensite region increased with increasing number of cycles. Thermodynamical simulations were used as basis for discussing the formation of α’ martensite. The effect of the α’ martensite on corrosion is also discussed.

• 11.
Dept of Industrial Engineering (DIN), University of Bologa, Italy.
Dept of Industrial Engineering (DIN), University of Bologa, Italy. Industrial Research Centre for Advanced Mechanics and Materials, University of Bologna, Italy. Dept of Industrial Engineering (DIN), University of Bologna, Italy. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Dept of Materials and Manufacturing, Jönköping University.
Effect of Microstructure and Overaging on the Tensile Behavior at Room and Elevated Temperature of C355-T6 Cast Aluminum Alloy2015Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 83, s. 626-634Artikel i tidskrift (Refereegranskat)

The present study was focused on the microstructural and mechanical characterization of the Al–Si–Cu–Mg C355 alloy, at room and elevated temperature. In order to evaluate the influence of microstructural coarseness on mechanical behavior, samples with different Secondary Dendrite Arm Spacing (SDAS) (20–25 μm for fine microstructure and 50–70 μm for coarse microstructure), were produced through controlled casting conditions. The tensile behavior of the alloy was evaluated at T6 condition and at T6 with subsequent high temperature exposure (41 h at 210 °C, i.e. overaging), both at room and elevated temperature (200 °C). Microstructural investigations were performed through optical and electron microscopy.

The results confirmed the important role of microstructure on the tensile behavior of C355 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Larger SDAS, related to lower solidification rates, modify microstructural features, such as eutectic Si morphology and size of the intermetallic phases, which in turn influence elongation to failure. Overaging before tensile testing induced coarsening of the strengthening precipitates, as observed by STEM analyses, with consequent reduction of the tensile strength of the alloy, regardless of SDAS. A more sensible decrease of tensile properties was registered at 200 °C testing temperature.

• 12.
Dept of Industrial Engineering (DIN), University of Bologa, Italy.
Dept of Industrial Engineering (DIN), University of Bologna, Italy. Dept of Industrial Engineering (DIN), University of Bologna, Italy. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Dept of Materials and Manufacturing, Jönköping University.
Microstructural and Mechanical Properties Characterization of Heat Treated and Overaged Cast A354 Alloy with Various SDAS at Room and Elevated Temperature2015Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 648, s. 340-349Artikel i tidskrift (Refereegranskat)

The aim of the present study was to carry out a microstructural and mechanical characterization of the A354 (Al–Si–Cu–Mg) cast aluminum alloy. The effect of microstructure on the tensile behavior was evaluated by testing samples with different Secondary Dendrite Arm Spacing, (SDAS) values (20–25 μm and 50–70 μm for fine and coarse microstructure, respectively), which were produced through controlled casting conditions. The tensile behavior of the alloy was evaluated both at room and elevated temperature (200 °C), in the heat treated and overaged (exposure at 210 °C for 41 h, after heat treatment) conditions. Optical, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) were used for microstructural investigations.

Experimental data confirmed the significant role of microstructural coarseness on the tensile behavior of A354 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Moreover, solidification rate influenced other microstructural features, such as the eutectic silicon morphology as well as the size of the intermetallic phases, which in turn also influenced elongation to failure. Coarsening of the strengthening precipitates was induced by overaging, as observed by STEM analyses, thus leading to a strong reduction of the tensile strength of the alloy, regardless of SDAS. Tensile properties of the alloy sensibly decrease at elevated temperature (200 °C) in all the investigated heat treatment conditions.

• 13.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Sandvik Materials Technology,Sandviken, Sweden .
Sandvik Materials Technology,Sandviken, Sweden . Sandvik Materials Technology,Sandviken, Sweden . Sandvik Materials Technology,Sandviken, Sweden .
Creep Behavior in A Newly Developed Heat Resistant Austenitic Stainless Steel2015Ingår i: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, E-ISSN 1613-7531, Vol. 160, nr 9, s. 400-405Artikel i tidskrift (Refereegranskat)

UNS S31035 austenitic stainless steel grade is a newly developed advanced heat resistant material for use in coal fired boilers at metal temperatures up to 700 °C. This new grade that has recently got two AMSE code cases shows good resistance to steam oxidation and flue gas corrosion and high creep rupture strength. This paper will mainly focus on the characterization of long term structure stability and performances such as the creep behaviors at different temperatures for up to 86,000 h at high temperatures. The creep damage mechanisms were studied using electron transmission microscopy, electron backscatter diffraction, and electron channeling contrast image analysis. The results show that the creep strength is related to the intragranular nano particles that act as obstacles for dislocation movements. Plastic deformation and transgranular fracture is the main creep fracture mechanism in the creep test samples of UNS S31035. The material has good creep ductility by formation of twins during the creep test. This material has been installed and tested in several European power plants, and has shown good performance. The material is an excellent alternative for superheaters and reheaters in future high-efficient coal fired boilers with design material temperatures up to 700 °C, instead of more costly nickel based alloy.

• 14.
Effects of decomposition route and microstructure on h-AlN formation rate in TiCrAlN alloys2017Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 691, s. 1024-1032Artikel i tidskrift (Refereegranskat)

The phase evolution of cubic (c), solid solution TixCr-0.37Al1-0.37-x N alloys with x = 0.03 and 0.16, and the kinetics of the hexagonal (h)-AlN formation are studied via in situ wide angle x-ray scattering experiments during high temperature (1000-1150 degrees C) annealing. Spinodal decomposition was observed in Ti0.16Cr0.36Al0.48N while Ti0.03Cr0.38Al0.59N decomposes through nucleation and growth of h-AlN, c-TiN and c-CrAlN. h-AlN is formed from c-CrAlN domains in both cases and the formation rate of h-AlN depends on the stability of the c-CrAlN domains. In Ti0.16Cr0.36Al0.48N, the c-CrAlN domains are stabilized by crystallographic coherency with the surrounding c-TiCrN in a microstructure originating from spinodal decomposition. This results in lower formation rates of h-AlN for this composition. These differences are reflected in higher activation energy for h-AlN formation in Ti0.16Cr0.36Al0.48N compared to Ti0.03Cr0.38Al0.59N. It also points out different stabilities of the intermediate phase c-CrAlN during phase decomposition of TiCrAlN alloys. Additional contributions to the low activation energy for formation of h-AlN in Ti0.03Cr0.38Al0.59N stems from precipitation at grain boundaries. (C) 2016 Elsevier B.V. All rights reserved.

• 15.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
Surface Integrity and Fatigue Performance of Nickel-based Superalloys2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

Due to global warming, the demand for more efficient gas turbines has increased. A way to achieve this, is by increasing the operating temperature of the gas turbine. Therefore, nickel-based superalloys have been developed to withstand these extreme temperatures and loads, especially in the hot sections. Today, the way of operating land-based gas turbines is changing. Instead of running for long periods of time, the operation is becoming more flexible, with ever-increasing cyclic loads and number of start and stop cycles. To handle the increased stress and cycles, component resistance to fatigue failures need to be improved.

Surface integrity is critical to fatigue performance, since fatigue cracks normally initiate at a surface. Machining changes the surface integrity which can result in worse fatigue resistance. The work presented in this Ph.D. thesis was conducted in collaboration with Siemens Industrial Turbomachinery AB in Finspång, Sweden. Surface integrity changes which are induced during machining and their effects on fatigue performance have been studied on the alloy Inconel 718. Inconel 718 is a widely-used nickel-based superalloy for high temperature applications in modern gas turbines.

Broaching, milling, and wire electrical discharge machining, related to component manufacturing in turbo machinery industries, were included in this study. Machining induced surface defects provide preferential sites for fatigue crack initiation which influence the fatigue performance of the alloy. If compressive residual stresses are induced during machining, they benefit the fatigue life by retarding fatigue crack initiation away from surface regions. Shot peening was performed on machined Inconel 718, by which high compressive residual stresses are deliberately induced. It results in enhanced fatigue performance.

The high temperatures in gas turbines generally deteriorate the surface integrity. Recrystallization often occurs in the highly deformed surface layer. Microstructural degradation, in the form of α-Cr precipitates, have also been frequently observed in the deformed surface and sub-surface microstructure. Oxidation at elevated temperatures degrades the surface integrity and thereby also the fatigue performance. Fatigue cracks are preferably initiated at oxidized surface carbides, if thermal exposure has been made prior to the test. It is even worse when high temperatures relax the beneficial surface compression induced by shot-peening and thereby lowering the fatigue resistance.

Machinability of a newly developed nickel-based superalloy, AD 730TM, and the surface integrity induced during turning have also been studied in this thesis project. AD 730TM is a candidate for turbine disc applications with an operating temperature above 650 °C. At such high temperatures, Inconel 718 is no longer stable and its mechanical properties start to degrade.

To summarize, the results from this thesis work show the importance of understanding surface integrity effects for fatigue applications, especially in harsh environments. Moreover, the knowledge gained through this work could be used for surface enhancement of turbine components which are subjected to a high risk of fatigue failure. These will contribute to more efficient and flexible power generation by gas turbines.

1. Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures
Öppna denna publikation i ny flik eller fönster >>Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures
2016 (Engelska)Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47A, nr 7, s. 3664-3676Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 A degrees C, 550 A degrees C, and 650 A degrees C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and alpha-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.

##### Ort, förlag, år, upplaga, sidor
Springer, 2016
##### Nyckelord
Structural integrity, Broaching, Inconel 718, Plastic deformation, Residual stresses, Thermal exposure, Superalloy
##### Nationell ämneskategori
Materialteknik Annan materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-111056 (URN)10.1007/s11661-016-3515-6 (DOI)000377434700041 ()
##### Anmärkning

The original title of this article when published in manuscript form was Structural integrity of broached Inconel 718 subjected to thermal exposure.

2. On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 718
Öppna denna publikation i ny flik eller fönster >>On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 718
2016 (Engelska)Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 671, s. 158-169Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

In this study, the conjoint effect of a broaching operation, similar to that used for machining fir-tree slots on turbine discs, and subsequent heat treatments at 550 °C and 650 °C on the fatigue performance and corresponding crack initiation behavior of forged Inconel 718 has been investigated. Four-point bending fatigue tests were conducted under load control on specimens of two groups, i.e. a polished group and a broached group, with totally six different surface conditions. Compared to the as-polished specimens, a beneficial effect of the broaching operation was found on the fatigue life due to the high compressive residual stresses on the broached surface which transfer the fatigue crack initiation from surface to sub-surface regions. Introducing a heat treatment generally deteriorated the fatigue performance of the alloy because of the oxidation assisted crack initiation, while the reduction in fatigue life was found to be more remarkable for the broached specimens, in particular when heat treated at 650 °C, as the thermal impact also led to a great relaxation of the compressive residual stresses; the combined effect, together with the substantial anomalies created by broaching on the surface, such as cracked carbides and machining grooves, caused an increased propensity to surface cracking in fatigue and consequently a loss of the lifetime. Furthermore, it was found that the occurrence of surface recrystallization at elevated temperatures in machined Inconel 718 could lead to intergranular oxidation, creating micro-notches as preferable sites for the fatigue crack initiation.

##### Nyckelord
Broaching, Inconel 718, Surface integrity, thermal impact, Fatigue, Crack initiation
##### Nationell ämneskategori
Annan materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-129843 (URN)10.1016/j.msea.2016.06.030 (DOI)000381165400016 ()
##### Anmärkning

Funding agencies: Faculty grant SFO-MAT-LiU at Linkoping University [2009-00971]; Siemens Industrial Turbomachinery AB

3. Nano-scale characterization of white layer in broached Inconel 718
Öppna denna publikation i ny flik eller fönster >>Nano-scale characterization of white layer in broached Inconel 718
2017 (Engelska)Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 684, s. 373-384Artikel i tidskrift (Refereegranskat) Published
##### Abstract [sv]

The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718.

TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ′ and γ′′ clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.

##### Ort, förlag, år, upplaga, sidor
Amsterdam: Elsevier, 2017
##### Nyckelord
Surface integrity; White layer; Broaching; Inconel 718; Adiabatic shear band; Mechanically-based subgrain rotation
##### Nationell ämneskategori
Materialkemi Oorganisk kemi Annan materialteknik Pappers-, massa- och fiberteknik Den kondenserade materiens fysik
##### Identifikatorer
urn:nbn:se:liu:diva-134123 (URN)10.1016/j.msea.2016.12.045 (DOI)000393938300045 ()
##### Anmärkning

Funding agencies: AForsk Foundation [15-334];  [2009-00971]

4. Surface Integrity and Fatigue Performance of Inconel 718 in Wire Electrical Discharge Machining
Öppna denna publikation i ny flik eller fönster >>Surface Integrity and Fatigue Performance of Inconel 718 in Wire Electrical Discharge Machining
2016 (Engelska)Ingår i: 3RD CIRP CONFERENCE ON SURFACE INTEGRITY, 2016, Vol. 45, s. 307-310Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

This paper presents a study to characterize the surface integrity in wire electrical discharge machining (EDM) of Inconel 718 and investigate its effect on the fatigue performance of the alloy in a four-point bending fatigue mode at room temperature. The EDM process generates a rough recast surface with multi-types of defects. Surface craters, micro-cracks and micro-voids within the recast layer have been found to be most detrimental from the point of view of fatigue as they could provide many preferential initiation sites for fatigue cracks. As a consequence, the specimens with an EDM cut surface show an approximately 30% decrease in fatigue life compared to those with a polished surface, and multiple crack origins were observed on the fracture surface. The high tensile residual stresses generated on the EDM cut surface, on the other hand, are also believed to be partly responsible for the loss in fatigue life of the alloy machined by EDM.

##### Serie
Procedia CIRP, ISSN 2212-8271
##### Nyckelord
wire electrical discharge machining (wire EDM), surface integrity, fatigue, crack initiation, Inconel 718
##### Nationell ämneskategori
Materialteknik Annan materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-130582 (URN)10.1016/j.procir.2016.02.053 (DOI)000417326500077 ()
##### Konferens
3rd CIRP Conference on Surface Integrity (CIRP CSI)8-10 June, 2016, Charlotte, USA
##### Anmärkning

Funding agencies: Siemens Industrial Turbomachinery AB; Strategic Faculty Grant AFM at Linkoping University

5. Effect of Cooling and Shot Peening on Residual Stresses and Fatigue Performance of Milled Inconel 718
Öppna denna publikation i ny flik eller fönster >>Effect of Cooling and Shot Peening on Residual Stresses and Fatigue Performance of Milled Inconel 718
2017 (Engelska)Ingår i: Residual Stresses 2016 ICRS 10 / [ed] T.M. Holden, O. Muránsky, and L. Edwards, 2017, Vol. 2, s. 13-18Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

The present study highlights the effect of cooling and post-machining surface treatment of shot peening on the residual stresses and corresponding fatigue life of milled superalloy Inconel 718. It was found that tensile residual stresses were created on the milled surface, regardless of the use of coolant, however, the wet milling operation led to a lower surface tension and a reduced thickness of the tensile layer. The shot peening performed on the dry-milled specimens completely annihilated the surface tensile residual tresses and introduced a high level of surface compression. A comparable fatigue life for the wet-milled specimens was obtained as compared with the specimens prepared by dry milling. This is very likely attributed to that the milling-induced surface damage with respect to cracked non-metallic inclusions is the predominant cause of the fatigue failure. The presence of the compressive layer induced by shot peening resulted in a significant increase of the fatigue life and strength, while the extent to which the lifetime was prolonged was decreased as the applied load was increased.

##### Serie
Materials Research Proceedings, ISSN 2474-395X
##### Nyckelord
Residual stresses, surface integrity, milling, shot peening, superalloys, fatigue
##### Nationell ämneskategori
Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-132001 (URN)10.21741/9781945291173-3 (DOI)000401041500003 ()978-1-9452-9116-6 (ISBN)
##### Konferens
10th International Conference on Residual Stresses ICRS-10, Sydney, Australia, 3-8 July 2016
##### Anmärkning

Funding agencies: Linkoping University [2009-00971]; Ytstruktur Arboga AB; Siemens Industrial Turbomachinery AB

• 16.
Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France. Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
Mechanical and thermodynamical study of a macroscopically coherent phase transition.Case of the martensitic transformation1991Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 1, s. C4-89-C4-94Artikel i tidskrift (Refereegranskat)

In the general framework of a macroscopically coherent phase transition, the mechanical and thermodynamical behaviour of a two-phase volume element under structural evolution will be investigated and discussed. The identification of internal entropy production will then allow to formulate a general evolution condition for such a system and the internal stress state will appear to influence strongly the transformation behaviour, via the interface. The case of a martensitic transformation is considered. From that rigourous mechanical approach, we obtain the thermodynamical balance equation used for martensitic transformation.

• 17.
Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France. Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France. Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
Micromechanical simulation of a martensitic transformaation by Finite Elements1991Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 1, s. C4-77-C4-82Artikel i tidskrift (Refereegranskat)

A micromechanical model describing the martensitic transformation on the grain scale has been developed, using Finite Elements. First results gained from the simulation illustrate how the morphological evolution within the grain is directly controlled by the internal stress state. The reversible and irreversible part of transformation "plasticity" strain and their evolution with the transformation can then be obtained from these calculations.

• 18.
Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France. Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France.
Martensitic transformation plasticity simulations by Finite Elements1994Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 4, s. C3-215-C3-220Artikel i tidskrift (Refereegranskat)

The mechanical behaviour associated to the martensitic transformation has been modelled using a 2D FE description. The martensite variants are constituted of different elements of the mesh and four different variants are allowed to transform in the grain. The transformation progress is prescribed using a thermodynamical criterion based on the maximal work associated to the variant formation. Transformation plasticity deformation and plates orientation patterns are obtained for three stress levels. These results are discussed in regard to the model used and the physical parameters introduced in the model.

• 19.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
Finite Element Analysis of Sheet Metal Assemblies: Prediction of Product Performance Considering the Manufacturing Process2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

This thesis concerns the development of methodologies to be used to simulate complete manufacturing chains of sheet components and the study of how different mechanical properties propagate and influence succeeding component performance.

Since sheet metal assemblies are a major constituent of a wide range of products it is vital to develop methodologies that enable detailed evaluation of assembly designs and manufacturing processes. The manufacturing process influences several key aspects of a sheet metal assembly, aspects such as shape fulfilment, variation and risk of material failure.

Developments in computer-aided engineering and computational resources have made simulation-based process and product development efficient and useful since it allows for detailed, rapid evaluation of the capabilities and qualities of both process and product. Simulations of individual manufacturing processes are useful, but greater benefits can be gained by studying the complete sequence of a product's manufacturing processes. This enables evaluation of the entire manufacturing process chain, as well as the final product. Moreover, the accuracy of each individual manufacturing process simulation is improved by establishing appropriate initial conditions, including inherited material properties.

In this thesis, a methodology of sequentially simulating each step in the manufacturing process of a sheet metal assembly is presented. The methodology is thoroughly studied using different application examples with experimental validation. The importance of information transfer between all simulation steps is also studied. Furthermore, the methodology is used as the foundation of a new approach to investigate the variation of mechanical properties in a sheet metal assembly. The multi-stage manufacturing process of the assembly is segmented, and stochastic analyses of each stage is performed and coupled to the succeeding stage in order to predict the assembly's final variation in properties.

Two additional studies are presented where the methodology of chaining manufacturing processes is utilised. The influence of the dual phase microstructure on non-linear strain recovery is investigated using a micromechanical approach that considers the annealing process chain. It is vital to understand the non-linear strain recovery in order to improve springback prediction. In addition, the prediction of fracture in a dual phase steel subjected to non-linear straining is studied by simulating the manufacturing chain and subsequent stretch test of a sheet metal component.

1. Finite element simulation of the manufacturing process chain of a sheet metal assembly
Öppna denna publikation i ny flik eller fönster >>Finite element simulation of the manufacturing process chain of a sheet metal assembly
2012 (Engelska)Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, nr 7, s. 1453-1462Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

An increasing number of components in automotive structures are today made from advanced high strength steel (AHSS). Since AHSS demonstrates more severe springback behaviour than ordinary mild steels, it requires more efforts to meet the design specification of the stamped parts. Consequently, the physical fine tuning of the die design and the stamping process can be time consuming. The trial-and-error development process may be shortened by replacing most of the physical try-outs with finite element (FE) simulations of the forming process, including the springback behaviour. Still it can be hard to identify when a stamped part will lead to an acceptable assembly with respect to the geometry and the residual stress state. In part since the assembling process itself will distort the components. To resolve this matter it is here proposed to extend the FE-simulation of the stamping process, to also include the first level sub-assembly stage. In this study a methodology of sequentially simulating each step in the manufacturing process of an assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparing with a physically manufactured assembly. The assembly is composed of three sheet metal components made from DP600 steel which are joined by spot welding. The components are designed to exhibit severe springback behaviour in order to put both the forming and subsequent assembling simulations to the test. The work presented here demonstrates that by using virtual prototyping it is possible to predict the final shape of an assembled structure.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2012
##### Nyckelord
Finite element simulation, Assembly, Sheet metal, Forming, Springback
##### Nationell ämneskategori
Teknik och teknologier
##### Identifikatorer
urn:nbn:se:liu:diva-77853 (URN)10.1016/j.jmatprotec.2012.02.012 (DOI)000304020800001 ()
##### Anmärkning

Funding Agencies|Swedish foundation for strategic research||ProViking programme||

2. The effects of forming history on sheet metal assembly
Öppna denna publikation i ny flik eller fönster >>The effects of forming history on sheet metal assembly
2014 (Engelska)Ingår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 7, nr 3, s. 305-316Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

As demand for faster product development increases, physical prototypes are replaced by virtual prototypes. By using finite element simulations to evaluate the functional behaviour of the product as well as its manufacturing process, more design alternatives can be evaluated while a considerably smaller number of physical prototypes are needed. As sheet metal assemblies are common in a wide range of products, reliable methods for predicting their properties are necessary. By sequentially simulating the complete manufacturing process chain of an assembly, early predictions concerning the geometry and material properties of the assembly can be made.

In this study a simulation-based sensitivity study is performed in order to investigate the influence of the forming history on the predictions of assembly properties. In the study, several simulations of the assembly stage are performed in which different types of forming histories are retained from the forming stage. The simulations of the assembly stage will range from a case with linear elastic conditions without forming history, to a case with the full forming history state and consistent material modelling throughout all simulations. It is found that the residual stress state is the most influential history variable from the forming stage. Especially for more complex geometries in which large residual stresses can be retained.

##### Ort, förlag, år, upplaga, sidor
Springer, 2014
##### Nyckelord
Finite element simulation, Assembly, Sheet metal, Forming, History variables, Chaining of manufacturing processes
##### Nationell ämneskategori
Teknik och teknologier
##### Identifikatorer
urn:nbn:se:liu:diva-78765 (URN)10.1007/s12289-013-1128-9 (DOI)000338323600004 ()
##### Anmärkning

On the day of the defence date of the Ph.D. thesis the status of this article was Manuscript.

Öppna denna publikation i ny flik eller fönster >>A study of the unloading behaviour of dual phase steel
2014 (Engelska)Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 602, s. 119-126Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

It is important to understand the strain recovery of a steel sheet in order to predict its springback behaviour. During strain recovery, the stress–strain relation is non-linear and the resulting unloading modulus is decreased. Moreover, the unloading modulus will degrade with increasing plastic pre-straining. This study aims at adding new knowledge on these phenomena and the mechanisms causing them. The unloading behaviour of the dual-phase steel DP600 is characterised experimentally and finite element (FE) simulations of a representative volume element (RVE) of the microstructure are performed. The initial stress and strain state of the micromechanical FE model is found by a simplified simulation of the annealing processes. It is observed from the experimental characterisation that the decrease of the initial stiffness of the unloading is the main reason for the degrading unloading modulus. Furthermore, the developed micromechanical FE model exhibits non-linear strain recovery due to local plasticity caused by interaction between the two phases.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2014
##### Nationell ämneskategori
Metallurgi och metalliska material Teknisk mekanik
##### Identifikatorer
urn:nbn:se:liu:diva-106318 (URN)10.1016/j.msea.2014.02.069 (DOI)000335098500015 ()
4. Prediction of fracture in a dual-phase steel subjected to non-linear straining
Öppna denna publikation i ny flik eller fönster >>Prediction of fracture in a dual-phase steel subjected to non-linear straining
2014 (Engelska)Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, nr 11, s. 2748-2758Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

In this work, selected fracture criteria are applied to predict the fracture of dualphase steel subjected to non-linear strain paths. Furthermore, the effects of manufacturing history are studied. Four fracture criteria were calibrated in three tests using standard specimens. The fracture criteria were first validated in the circular Nakajima test. A second validation test case was included in order to validate fracture prediction for non-linear strain paths. In this test a sheet metal component was manufactured and subsequently stretched until it fractured. All fracture criteria included in this study predict fracture during the Nakajima test with reasonable accuracy. In the second validation test however, the different fracture criteria show considerable diversity in accumulated damage during manufacturing which caused substantial scatter of the fracture prediction in the subsequent stretching. This shows that manufacturing history influences the prediction of fracture.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2014
##### Nyckelord
Sheet metal failure, high strength steels, forming limits, non-linear strain paths, forming history
##### Identifikatorer
urn:nbn:se:liu:diva-105211 (URN)10.1016/j.jmatprotec.2014.05.028 (DOI)000340300400059 ()
##### Anmärkning

Funders: SSF ProViking project entitled "SuperLight Steel Structures"

5. Stochastic analysis of a sheet metal assembly considering its manufacturing process
Öppna denna publikation i ny flik eller fönster >>Stochastic analysis of a sheet metal assembly considering its manufacturing process
2014 (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
##### Abstract [en]

In order to accurately predict the mechanical properties of a sheet metal assembly it has been shown important to account for how the geometry and material properties are affected by the manufacturing process. It is also of a great interest to predict the variations of important responses, and how these variations depend on the manufacturing process.

In this study, the variation of properties during the multi-stage manufacturing process of a sheet metal assembly is evaluated and the variability of a response due to loading is studied. A methodology to investigate how variations evolve during the assembling process is presented. The multi-stage assembling process is virtually segmented, such that stochastic analyses of each process stage are performed and coupled to succeeding stages in order to predict the variation in properties of the final assembly. The methodology is applied to an industrial assembly and experimental validations have been conducted. The prediction of the geometry of the final assembly is in good agreement with the experimental results, while the prediction of the variation of this geometry is in fair agreement.

##### Nyckelord
Finite element simulation, Assembly, Sheet metal, Forming, Monte Carlo analysis, Chaining of manufacturing processes
##### Nationell ämneskategori
Metallurgi och metalliska material Teknisk mekanik
##### Identifikatorer
urn:nbn:se:liu:diva-106636 (URN)
• 20.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska högskolan.
Stochastic analysis of a sheet metal assembly considering its manufacturing process2014Manuskript (preprint) (Övrigt vetenskapligt)

In order to accurately predict the mechanical properties of a sheet metal assembly it has been shown important to account for how the geometry and material properties are affected by the manufacturing process. It is also of a great interest to predict the variations of important responses, and how these variations depend on the manufacturing process.

In this study, the variation of properties during the multi-stage manufacturing process of a sheet metal assembly is evaluated and the variability of a response due to loading is studied. A methodology to investigate how variations evolve during the assembling process is presented. The multi-stage assembling process is virtually segmented, such that stochastic analyses of each process stage are performed and coupled to succeeding stages in order to predict the variation in properties of the final assembly. The methodology is applied to an industrial assembly and experimental validations have been conducted. The prediction of the geometry of the final assembly is in good agreement with the experimental results, while the prediction of the variation of this geometry is in fair agreement.

• 21.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
Saab AB, Linköping, Sweden. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
A study of the unloading behaviour of dual phase steel2014Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 602, s. 119-126Artikel i tidskrift (Refereegranskat)

It is important to understand the strain recovery of a steel sheet in order to predict its springback behaviour. During strain recovery, the stress–strain relation is non-linear and the resulting unloading modulus is decreased. Moreover, the unloading modulus will degrade with increasing plastic pre-straining. This study aims at adding new knowledge on these phenomena and the mechanisms causing them. The unloading behaviour of the dual-phase steel DP600 is characterised experimentally and finite element (FE) simulations of a representative volume element (RVE) of the microstructure are performed. The initial stress and strain state of the micromechanical FE model is found by a simplified simulation of the annealing processes. It is observed from the experimental characterisation that the decrease of the initial stiffness of the unloading is the main reason for the degrading unloading modulus. Furthermore, the developed micromechanical FE model exhibits non-linear strain recovery due to local plasticity caused by interaction between the two phases.

• 22.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
Controlling the growth of nanoparticles produced in a high power pulsed plasma2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

Nanotechnology can profoundly benefit our health, environment and everyday life. In order to make this a reality, both technological and theoretical advancements of the nanomaterial synthesis methods are needed. A nanoparticle is one of the fundamental building blocks in nanotechnology and this thesis describes the control of the nucleation, growth and oxidation of titanium particles produced in a pulsed plasma. It will be shown that by controlling the process conditions both the composition (oxidationstate) and size of the particles can be varied. The experimental results are supported by theoretical modeling.

If processing conditions are chosen which give a high temperature in the nanoparticle growth environment, oxygen was found to be necessary in order to nucleate the nanoparticles. The two reasons for this are 1: the lower vapor pressure of a titanium oxide cluster compared to a titanium cluster, meaning a lower probability of evaporation, and 2: the ability of a cluster to cool down by ejecting an oxygen atom when an oxygen molecule condenses on its surface. When the oxygen gas flow was slightly increased, the nanoparticle yield and oxidation state increased. A further increase caused a decrease in particle yield which is attributed to a slight oxidation ofthe cathode. By varying the oxygen flow, it was possible to control the oxidation state of the nanoparticles without fully oxidizing the cathode. Pure titanium nanoparticles could not be produced in a high vacuum system because oxygen containing gases such as residual water vapour have a profound influence on nanoparticle yield and composition. In an ultrahigh vacuum system titanium nanoparticles without significantoxygen contamination were produced by reducing the temperature of the growth environment and increasing the pressure of an argon-helium gas mixture within whichthe nanoparticles grew. The dimer formation rate necessary for this is only achievable at higher pressures. After a dimer has formed, it needs to grow by colliding with a titanium atom followed by cooling by collisions with multiple buffer gas atoms. The condensation event heats up the cluster to a temperature much higher than the gas temperature, where it is during a short time susceptible to evaporation. When the clusters’ internal energy has decreased by collisions with the gas to less than the energy required to evaporate a titanium atom, it is temporarily stable until the next condensation event occurs. The temperature difference by which the cluster has to cool down before it is temporarily stable is exactly as many kelvins as the gas temperature.The addition of helium was found to decrease the temperature of the gas, making it possible for nanoparticles of pure titanium to grow. The process window where this is possible was determined and the results presented opens up new possibilities to synthesize particles with a controlled contamination level and deposition rate.The size of the nanoparticles has been controlled by three means. The first is to change the electrical potential around the growth zone, which allows for size (diameter) control in the order of 25 to 75 nm without influencing the oxygen content of the particles. The second means is by increasing the pressure which decreases the ambipolar diffusion rate of the ions resulting in a higher growth material density. By doing this, the particle size can be increased from 50 to 250 nm, however the oxygen content also increases with increasing pressure when this is done in a high vacuum system. The last means of size control was by adding a helium flow to the process where higher flows resulted in smaller nanoparticle sizes.

When changing the pressure in high vacuum, the morphology of the nanoparticles could be controlled. At low pressures, highly faceted near spherical particles were produced. Increasing the pressure caused the formation of cubic particles which appear to ‘fracture’ at higher pressures. At the highest pressure investigated, the particles became poly-crystalline with a cauliflower shape and this morphology was attributed to a lowad atom mobility.

The ability to control the size, morphology and composition of the nanoparticles determines the success of applying the process to manufacture devices. In related work presented in this thesis it is shown that 150-200 nm molybdenum particles with cauliflower morphology were found to scatter light in which made them useful in photovoltaic applications, and the size of titanium dioxide nanoparticles were found to influence the selectivity of graphene based gas sensors.

1. Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
Öppna denna publikation i ny flik eller fönster >>Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
2015 (Engelska)Ingår i: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 17, nr 9, s. 353-Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Ti-O nanoparticles have been synthesized via hollow cathode sputtering in an Ar-O-2 atmosphere using high power pulsing. It is shown that the stoichiometry and the size of the nanoparticles can be varied independently, the former through controlling the O-2 gas flow and the latter by the independent biasing of two separate anodes in the growth zone. Nanoparticles with diameters in the range of 25-75 nm, and with different Ti-O compositions and crystalline phases, have been synthesized.

##### Ort, förlag, år, upplaga, sidor
Springer Verlag (Germany), 2015
##### Nyckelord
Titanium dioxide; TiO2; Reactive sputtering; Size control; Composition control; Gas flow sputtering; Aerosols
Fysik
##### Identifikatorer
urn:nbn:se:liu:diva-121300 (URN)10.1007/s11051-015-3158-3 (DOI)000360245300002 ()
##### Anmärkning

Funding Agencies|Knut and Alice Wallenberg foundation [KAW 2014.0276]; Swedish Research Council via the Linkoping Linneaus Environment LiLi-NFM [2008-6572]

2. The influence of pressure and gas flow on size and morphology of titanium oxide nanoparticles synthesized by hollow cathode sputtering
Öppna denna publikation i ny flik eller fönster >>The influence of pressure and gas flow on size and morphology of titanium oxide nanoparticles synthesized by hollow cathode sputtering
2016 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 120, nr 4, s. 044308-Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Titanium oxide nanoparticles have been synthesized via sputtering of a hollow cathode in an argon atmosphere. The influence of pressure and gas flow has been studied. Changing the pressure affects the nanoparticle size, increasing approximately proportional to the pressure squared. The influence of gas flow is dependent on the pressure. In the low pressure regime (107 amp;lt;= p amp;lt;= 143 Pa), the nanoparticle size decreases with increasing gas flow; however, at high pressure (p = 215 Pa), the trend is reversed. For low pressures and high gas flows, it was necessary to add oxygen for the particles to nucleate. There is also a morphological transition of the nanoparticle shape that is dependent on the pressure. Shapes such as faceted, cubic, and cauliflower can be obtained. Published by AIP Publishing.

##### Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2016
##### Nationell ämneskategori
Strömningsmekanik och akustik
##### Identifikatorer
urn:nbn:se:liu:diva-131710 (URN)10.1063/1.4959993 (DOI)000382405400029 ()
##### Anmärkning

Funding Agencies|Knut and Alice Wallenberg foundation [KAW 2014.0276]; Swedish Research Council via the Linkoping Linneaus Environment LiLi-NFM [2008-6572]

• 23.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
Titanium oxide nanoparticle production using high power pulsed plasmas2016Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)

This thesis covers fundamental aspects of process control when growing titanium oxide nanoparticles in a reactive sputtering process. It covers the influence of oxygen containing gas on the oxidation state of the cathode from which the growth material is ejected, as well as its influence on the particles oxidation state and their nucleation. It was found that a low degree of reactive gases was necessary for nanoparticles of titanium to nucleate. When the oxygen gas was slightly increased, the nanoparticle yield and particle oxygen content increased. A further increase caused a decrease in particle yield which was attributed to a slight oxidation of the cathode. By varying the oxygen flow to the process, it was possible to control the oxygen content of the nanoparticles without fully oxidizing the cathode. Because oxygen containing gases such as residual water vapour has a profound influence on nanoparticle yield and composition, the deposition source was re-engineered to allow for cleaner and thus more stable synthesis conditions.

The size of the nanoparticles has been controlled by two means. The first is to change electrical potentials around the growth zone, which allows for nanoparticle size control in the order of 25-75 nm. This size control does not influence the oxygen content of the nanoparticles. The second means of size control investigated was by increasing the pressure. By doing this, the particle size can be increased from 50 – 250 nm, however the oxygen content also increases with pressure. Different particle morphologies were found by changing the pressure. At low pressures, mostly spherical particles with weak facets were produced. As the pressure increased, the particles got a cubic shape. At higher pressures the cubic particles started to get a fractured surface. At the highest pressure investigated, the fractured surface became poly-crystalline, giving a cauliflower shaped morphology.

1. Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
Öppna denna publikation i ny flik eller fönster >>Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
2015 (Engelska)Ingår i: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 17, nr 9, s. 353-Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Ti-O nanoparticles have been synthesized via hollow cathode sputtering in an Ar-O-2 atmosphere using high power pulsing. It is shown that the stoichiometry and the size of the nanoparticles can be varied independently, the former through controlling the O-2 gas flow and the latter by the independent biasing of two separate anodes in the growth zone. Nanoparticles with diameters in the range of 25-75 nm, and with different Ti-O compositions and crystalline phases, have been synthesized.

##### Ort, förlag, år, upplaga, sidor
Springer Verlag (Germany), 2015
##### Nyckelord
Titanium dioxide; TiO2; Reactive sputtering; Size control; Composition control; Gas flow sputtering; Aerosols
Fysik
##### Identifikatorer
urn:nbn:se:liu:diva-121300 (URN)10.1007/s11051-015-3158-3 (DOI)000360245300002 ()
##### Anmärkning

Funding Agencies|Knut and Alice Wallenberg foundation [KAW 2014.0276]; Swedish Research Council via the Linkoping Linneaus Environment LiLi-NFM [2008-6572]

• 24.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
SP Technical Research Institute of Sweden, Box 857, 501 15 Borås, Sweden/School of Engineering, Jönköping University, Sweden. ENKOTEC A/S, Denmark. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
Electroplating of nickel in grooves under the influence of low and medium frequency ultrasound2011Ingår i: Journal for Electrochemistry and Plating Technology, ISSN 1866-7406, Vol. 1, nr 3, s. 19-28Artikel i tidskrift (Refereegranskat)

The effect of ultrasonics on filling properties has been studied by Ni electroplating from a sulphamate electrolyte in high aspect ratio grooves. The experiments have been performed with two different modes of ultrasound: a) 25 kHz ultrasound with an effect of 225 W directed perpendicular to the substrate surface; b) ultrasonic standing waves of 100 kHz and 400 kHz parallel to the substrate surface. It was found that both methods improve the filling in grooves that are between 0.35 and 1 mm wide with aspect ratios between 0.6 and 3, compared to electroplating with conventional agitation. Under the investigated conditions the 400 kHz standing wave parallel to the surface was most efficient to improve filling of grooves.

• 25.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Barriers to and Drivers for Improved Energy Efficiency in the Swedish Aluminium Industry and Aluminium Casting Foundries2019Ingår i: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 11, nr 7, artikel-id 2043Artikel i tidskrift (Refereegranskat)

Industrial energy efficiency is important for reducing CO2 emissions and could be a competitive advantage for companies because it can reduce costs. However, cost-effective energy efficiency measures are not always implemented because there are barriers inhibiting their implementation. Drivers for energy efficiency could provide means for overcoming these barriers. The aim of this article was to study the importance of different barriers to and drivers for improved energy efficiency in the Swedish aluminium industry and foundries that cast aluminium. Additionally, the perceived usefulness of different information sources on energy efficiency measures was studied. The data were collected through a questionnaire covering 39 barriers and 48 drivers, divided into different categories. Both the aluminium and foundry industries considered technological and economic barriers as the most important categories. The most important category of drivers for the aluminium industry was organisational drivers, while the foundries rated economic drivers as the most important. Colleagues within the company, the company group and sector, and the trade organisation were considered the most useful information sources. Important factors for driving work with improved energy efficiency included access to knowledge within the company, having a culture within the company promoting energy efficiency, and networking within the sector. The policy implications identified included energy labelling of production equipment, the law on energy audit in large companies and subsidy for energy audits in small- and medium-sized companies, voluntary agreements that included long-term energy strategies, increased taxes to improve the cost-effectiveness of energy efficiency measures, and EUs Emission Trading System.

• 26.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Energy Efficiency in the Supply Chains of the Aluminium Industry: The Cases of Five Products Made in Sweden2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 2, s. 245-Artikel i tidskrift (Refereegranskat)

Improved energy efficiency in supply chains can reduce both environmental impact and lifecycle costs, and thus becomes a competitive advantage in the work towards a sustainable global economy. Viewing the supply chain as a system provides the holistic perspective needed to avoid sub-optimal energy use. This article studies measures relating to technology and management that can increase energy efficiency in the supply chains of five aluminium products made in Sweden. Additionally, energy efficiency potentials related to the flows of material, energy, and knowledge between the actors in the supply chains are studied. Empirical data was collected using focus group interviews and one focus group per product was completed. The results show that there are several areas for potential energy efficiency improvement; for example, product design, communication and collaboration, transportation, and reduced material waste. Demands from other actors that can have direct or indirect effects on energy use in the supply chains were identified. Despite the fact that companies can save money through improved energy efficiency, demands from customers and the authorities would provide the additional incentives needed for companies to work harder to improve energy efficiency.

• 27.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Impact analysis of energy efficiency measures in the electrolysis process in primary aluminium production2019Ingår i: WEENTECH Proceedings in Energy, 2019, Vol. 4(2), s. 177-184Konferensbidrag (Refereegranskat)

The Paris Agreement includes the goals of ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels’ and ‘making finance flows consistent with a pathway towards low greenhouse gas emissions’. Industrial energy efficiency will play an important role in meeting those goals as well as becoming a competitive advantage due to reduced costs for companies. The aluminium industry is energy intensive and uses fossil fuels both for energy purposes and as reaction material. Additionally, the aluminium industry uses significant amounts of electricity. The electrolysis process in the primary production of aluminium is the most energy- and carbon-intensive process within the aluminium industry. The aim of this paper is to study the effects on primary energy use, greenhouse gas emissions and costs when three energy efficiency measures are implemented in the electrolysis process. The effects on the primary energy use, greenhouse gas emissions and costs are calculated by multiplying the savings in final energy use by a primary energy factor, emissions factor and price of electricity, respectively. The results showed significant savings in primary energy demand, greenhouse gas emissions and cost from the implementation of the three measures. These results only indicate the size of the potential savings and a site-specific investigation needs to be conducted for each plant. This paper is a part of a research project conducted in close cooperation with the Swedish aluminium industry.

• 28.
Siemens Industrial Turbomachinery AB, Finspong, Sweden.
Siemens Industrial Turbomachinery AB, Finspong, Sweden.
Constitutive Behaviour of IN738LC Under TMF Cycling With and Without Intermediate Ageing2007Ingår i: Proceedings of the ASME Turbo Expo [Volume 5: Turbo Expo 2007], New York: ASME Press, 2007, s. 131-135Konferensbidrag (Refereegranskat)

Out of Phase Thermo Mechanical Fatigue (OP TMF) 100–950°C tests with 5 min hold time, some including intermediate ageing for 4000h at 950°C after 25 cycles, have been performed on IN738LC at Siemens Industrial Turbomachinery (SIT) AB. In the standard tests, the variation in stress range during the tests was neutral. When tests with intermediate ageing were added to the analysis, the combination of test data strongly suggest that the neutral response above was because of a fairly even competition between softening due to degradation (particle coarsening etc.) and work hardening. We have concluded that the work hardening occuring for a lab hold time of 5 min. will be insignificant under more realistic, i.e. component-near, hold times. Based on this, we have devised a method for reduction of lab TMF test results, with their too short hold times, to handle actual, i.e. significantly longer, component hold times.

• 29.
Swerea IVF AB, Mölndal, Sweden.
Swerea IVF AB, Mölndal, Sweden. Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska fakulteten. Termisk Systemteknik AB, Linköping, Sweden. Termisk Systemteknik AB, Linköping, Sweden.
Selective Laser Melting Process Monitoring by Means of Thermography2018Ingår i: Proceedings of Euro Powder Metallurgy Congress (Euro PM), European Powder Metallurgy Association (EPMA) , 2018, artikel-id 3957771Konferensbidrag (Refereegranskat)

Selective laser melting (SLM) enables production of highly intricate components. From this point of view, the capabilities of this technology are known to the industry and have been demonstrated in numerous applications. Nonetheless, for serial production purposes the manufacturing industry has so far been reluctant in substituting its conventional methods with SLM. One underlying reason is the lack of simple and reliable process monitoring methods. This study examines the feasibility of using thermography for process monitoring. To this end, an infra-red (IR) camera was mounted off-axis to monitor and record the temperature of every layer. The recorded temperature curves are analysed and interpreted with respect to different stages of the process. Furthermore, the possibility of detecting variations in laser settings by means of thermography is demonstrated. The results show that once thermal patterns are identified, this data can be utilized for in-process and post-process monitoring of SLM production.

• 30.
Luleå University of Technology.
Yonsei University. Argonne National Laboratory. Argonne National Laboratory. Luleå University of Technology.
Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading2010Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, s. 734-744Artikel i tidskrift (Refereegranskat)

The lattice strain tensor evolution for single bulk grains of austenite and ferrite in a duplex stainless steel during tensile loading to 0.02 applied strain has been investigated using in situ high-energy X-ray measurements and finite-element modeling. Single-grain X-ray diffraction lattice strain data for the eight austenite and seven ferrite grains measured show a large variation of residual lattice strains, which evolves upon deformation to the point where some grains with comparable crystallographic orientations have lattice strains different by 1.5 × 10−3, corresponding to a stress of 300 MPa. The finite-element simulations of the 15 measured grains in three different spatial arrangements confirmed the complex deformation constraint and importance of local grain environment.

• 31.
Northeastern Univ, Peoples R China.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Northeastern Univ, Peoples R China. Northeastern Univ, Peoples R China. Northeastern Univ, Peoples R China.
Microstructural and textural evolutions in multilayered Ti/Cu composites processed by accumulative roll bonding2019Ingår i: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 35, nr 6, s. 1165-1174Artikel i tidskrift (Refereegranskat)

Ti/Cu multilayered composites were fabricated via accumulative roll bonding (ARB). During co-deformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of shear bands. Transmission electron microscopy showed that with increasing ARB cycles, grains in Ti were significantly refined even though dynamic recrystallization has occurred. For Cu the significant grain refinement was only found within the shear banded region when the composite was processed after five ARB cycles. Due to the diffusion of Cu atoms into Ti at the heterophase inter faces, amorphization with a width less than 10 nm was identified even in the composite processed by one cycle. At higher ARB cycles, the width of amorphous region increased and intermetallic compounds CuTi appeared from the region. The lattice defects introduced at the heterophase interfaces under roll bonding was responsible for the formation of the nano-scaled compounds. X-ray diffraction showed that an abnormal {11 (2) over bar0} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {11 (2) over bar0} fiber favored the prismatic amp;lt;aamp;gt; slip for Ti. Tensile tests revealed the elevated strength without a substantial sacrifice of ductility in the composites during ARB. The unique mechanical properties were attributed to the significantly refined grains in individual metals, the good bonding between the constituent metals, as well as the development of an abnormal {11 (2) over bar0} fiber texture in Ti layers. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science amp; Technology.

• 32.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem. Linköpings universitet, Tekniska fakulteten.
Energy efficient supply chain of an aluminium product in Sweden – What can be done in-house and between the companies?2018Ingår i: eceee 2018 Industrial Summer Study proceedings / [ed] Therese Laitinen Lindström, Ylva Blume & Nina Hampus, Stockholm, Sweden: European Council for an Energy Efficient Economy (ECEEE), 2018, s. 369-377Konferensbidrag (Refereegranskat)

According to the Energy Efficiency Directive executed by the European Union, each member state is obliged to set a national target on energy efficiency. This requirement constitutes the basis for governments to formulate policy measures directed towards industrial companies. Such policy measures, along with the demand for cost-effective production to remain competitive on the market, motivates industrial companies to improve their energy efficiency. The aluminium industry is energy intensive and consumes substantial amounts of electricity and fossil fuels, resulting in both direct and indirect greenhouse gas emissions. This paper presents a study of the production of an aluminium product in Sweden in terms of implemented energy efficiency measures in the supply chain and potential areas for further improvement. Most previous studies have focused on energy efficiency measures in individual companies (value chains). However, this paper presents and analyses energy efficiency measures not only in each individual company but also in the entire supply chain of the product. The supply chain studied starts with secondary aluminium production followed by the production of a part of an automobile motor and ends with installing the motor detail in a car. Empirical data were gathered through a questionnaire and a focus group. The study shows the great potential for further energy efficiency improvements in the value chains of each individual company and in the whole supply chain. The work shown here is a part of a larger research project performed in close cooperation with the Swedish aluminium industry.

• 33.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
Failure mechanisms in APS and SPS thermal barrier coatings during cyclic oxidation and hot corrosion2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)

Thermal Barrier Coatings (TBCs) are advanced material systems that are being used in the hot sections of gas turbines such as combustor, turbine blades, and vanes. The top ceramic coating in TBCs provides insulation against the hot gases and the intermediate metallic bond coat provides oxidation and corrosion resistance to the underlying turbine components.

Durability of thermal barrier coatings is very important for the overall performance of the gas turbine. TBCs can fail in several different ways and there is a combination of more than one failure mechanism in most situations. One of the most widely used TBC is atmospheric plasma sprayed (APS) yttria stabilized zirconia (YSZ). Both the deposition technique and the TBC material have certain limitations. The main aim of this research is to study new TBC materials and/or new deposition techniques and compare with the conventional YSZ and understand their failure mechanisms during cyclic oxidation and hot corrosion.

Thermal cyclic oxidation of a newly developed high purity nano YSZ thermal barrier coating has been studied. Cross sectional analysis of exposed as well as completely failed samples showed a mixed-type failure caused by crack propagation parallel to the bond coat/top coat interface. The majority of the damage occurred towards the end of the coating life. A finite element model has been developed to study the probability of crack growth along different paths that leads to the final failure.

Hot corrosion mechanism in suspension plasma sprayed two-layer gadolinium zirconate/YSZ, three-layer dense gadolinium zirconate/gadolinium zirconate/YSZ, and a single-layer YSZ has been studied in the presence of sodium sulfate and vanadium pentoxide. The test results showed that gadolinium zirconate coatings were more susceptible to corrosion compared to YSZ coatings despite gadolinium zirconate coatings having lower reactivity with the corrosive salts.

Thermal cycling behavior of a high chromium bond coat has been studied. Cross-sectional analysis showed formation of sandwich type microstructure with chromium rich oxide and alumina as the top and the bottom layers.

Inter-diffusion of minor elements between different MCrAlY coatings – substrate systems has been studied using, diffusion simulation software, DICTRA. The simulation results showed that the diffusion of minor elements in the coatings is dependent on the rate of β phase depletion in the beginning. After the depletion of β phase there was no clear dependence of the coating composition on the diffusion of minor elements.

1. Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
Öppna denna publikation i ny flik eller fönster >>Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
2017 (Engelska)Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, nr 1, s. 140-149Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

This study investigates the corrosion resistance of two-layer Gd2Zr2O7/YSZ, three-layer dense Gd2Zr2O7/ Gd2Zr2O7/YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 µm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900 °C for 8 h using V2O5 and Na2SO4 as corrosive salts at a concentration of approximately 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd2Zr2O7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ.

##### Ort, förlag, år, upplaga, sidor
New York: Springer, 2017
##### Nyckelord
gadolinium zirconatehot corrosionmulti-layer thermal barrier coatingssuspension plasma sprayingvanadium pentoxide + sodium sulfate
##### Nationell ämneskategori
Korrosionsteknik Bearbetnings-, yt- och fogningsteknik Materialkemi
##### Identifikatorer
urn:nbn:se:liu:diva-134375 (URN)10.1007/s11666-016-0486-5 (DOI)000392060300014 ()
##### Anmärkning

Funding agencies: Vinnova in Sweden

2. Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat
Öppna denna publikation i ny flik eller fönster >>Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat
2016 (Engelska)Ingår i: Proceedings of the International Thermal Spray Conference (ITSC), 2016, Vol. 324, s. 273-278Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

Thermal barrier coatings (TBCs) were air-plasma sprayed onto Hastelloy X substrates. The TBCs consisted of a high-Cr MCrAlY (M for Ni and Co) bond coat and a yttria-stabilized zirconia (YSZ) top coat. The TBC samples were thermally cycled between 100 ºC and 1100 ºC with 1 hour dwell time at 1100 ºC. The thermal fatigue failure of the TBCs was investigated via microstructure analyses. The final fatigue failure of the TBCs was caused by the formation of interface-parallel cracks in the YSZ top coat. The formation of the cracks was found to be strongly related to the oxidation behaviour of the MCrAlY bond coat. The development of the oxide layers was therefore studied in detail. A thermokinetic model was also used to deepen the understanding on the elemental diffusion behavior in the materials.

##### Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik Metallurgi och metalliska material Materialkemi Kompositmaterial och -teknik
##### Identifikatorer
urn:nbn:se:liu:diva-134377 (URN)
##### Konferens
International Thermal Spray Conference (ITSC), May 10-12, 2016, China
• 34.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
Thermal Barrier Coatings: Failure Mechanisms and Life Prediction2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

Thermal barrier coatings (TBCs) use in the hot sections of gas turbine engine enables them to run at higher temperatures, and as a consequence, achieve higher thermal efficiency. For full operational exploitation of TBCs, understanding their failure and knowing the service life is essential. The broad objective of the current research is to study the failure mechanisms of new TBC materials and deposition techniques during corrosion and thermal cycling and to develop life models capable of predicting the final failure during thermal cycling.

Yttria-stabilized zirconia (YSZ) has constraints such as limited operation temperature, despite being the current industry standard. Pyrochlores of A2B2O7 type have been suggested as a potential replacement for YSZ and were studied in this work. Additionally, improvements to the conventional YSZ in the form of nanostructured YSZ were also explored. The requirement for the new deposition process comes from the fact that the existing low-cost deposition processes, like atmospheric plasma spray (APS), generally exhibit lower strain tolerance. A relatively new technique, suspension plasma spray (SPS), known to be promising with better strain tolerance, has been studied in this work.

At the gas turbine operating conditions, TBCs degrade and eventually fail. Common failure observed in gas turbines can be due to corrosion, thermal mismatch between the ceramic and the metallic layers, and bond coat oxidation during thermal cycling. SPS and APS TBCs were subjected to different test conditions to understand their corrosion behavior. A study on the multi-layered SPS TBCs in the presence of V2O5+Na2SO4 showed that YSZ based SPS coatings were less susceptible to corrosion damage compared to Gd2Zr2O7 SPS TBCs. A study on the influence of a sealing layer in multi-layered SPS TBCs in the presence of Na2SO4+NaCl showed that the sealing layer is ineffective if the material used for sealing is inert to the molten salts. A new study on the influence of corrosion, caused by a mixed-gas atmosphere, on the thermal cycling fatigue life of SPS TBCs was conducted. Results showed that corrosive products grew inside the top coat close to the bond coat/top coat interface along with accelerated growth of alumina. These, together, reduced the TCF life of corrosion exposed samples significantly. Finally, a study on the influence of salt concentration and temperature on a thin (dense) and a thick (porous) coating showed that thick and porous coatings have lower corrosion resistance than the thin and dense coatings. Additionally, a combination of low temperature and high salt concentration was observed to cause more damage.

Thermal cycling studies were done with the objective of understanding the failure mechanisms and developing a life model. A life model based on fracture mechanics approach has been developed by taking into account different crack growth paths during thermal cycling, sintering of the top coat, oxidation of the bond coat and the thermal mismatch stresses. Validation of such a life model by comparing to the experimental results showed that the model could predict the TCF life reasonably well at temperatures of 1100 °C or below. At higher temperatures, the accuracy of the model became worse. As a further development, a simplified crack growth model was established. This simplified model was shown to be capable of predicting the TCF life as well as the effect of hold times with good accuracy.

1. Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
Öppna denna publikation i ny flik eller fönster >>Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
2017 (Engelska)Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, nr 1, s. 140-149Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

This study investigates the corrosion resistance of two-layer Gd2Zr2O7/YSZ, three-layer dense Gd2Zr2O7/ Gd2Zr2O7/YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 µm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900 °C for 8 h using V2O5 and Na2SO4 as corrosive salts at a concentration of approximately 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd2Zr2O7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ.

##### Ort, förlag, år, upplaga, sidor
New York: Springer, 2017
##### Nyckelord
gadolinium zirconatehot corrosionmulti-layer thermal barrier coatingssuspension plasma sprayingvanadium pentoxide + sodium sulfate
##### Nationell ämneskategori
Korrosionsteknik Bearbetnings-, yt- och fogningsteknik Materialkemi
##### Identifikatorer
urn:nbn:se:liu:diva-134375 (URN)10.1007/s11666-016-0486-5 (DOI)000392060300014 ()
##### Anmärkning

Funding agencies: Vinnova in Sweden

2. Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C
Öppna denna publikation i ny flik eller fönster >>Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C
2019 (Engelska)Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, nr 1-2, s. 212-222Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate + yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate + YSZ over YSZ. Cyclic corrosion tests were conducted between 25 and 900 °C with an exposure time of 8 h at 900 °C. 75 wt.% Na2SO4 + 25 wt.% NaCl were used as the corrosive salts at a concentration of 6 mg/cm2. Scanning electron microscopy analysis of the samples’ cross sections showed that severe bond coat degradation had taken place for both the TBC systems, and the extent of bond coat degradation was relatively higher in the triple-layer system. It is believed that the sealing layer in the triple-layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the sample edges and caused damage to develop relatively more from the edge.

##### Nyckelord
columnar microstructure, composite of gadolinium zirconate and YSZ, hot corrosion, suspension plasma spray
##### Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
##### Forskningsämne
TEKNIK, Produktions- och materialteknik; Produktionsteknik
##### Identifikatorer
urn:nbn:se:liu:diva-154778 (URN)10.1007/s11666-018-0780-5 (DOI)000456599500019 ()2-s2.0-85055998259 (Scopus ID)
VINNOVA
##### Anmärkning

This article is an invited paper selected from presentations at the 2018 International Thermal Spray Conference, held May 7-10, 2018, in Orlando, Florida, USA, and has been expanded from the original presentation.

3. Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO4
Öppna denna publikation i ny flik eller fönster >>Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO4
2016 (Engelska)Ingår i: JOURNAL OF CERAMIC SCIENCE AND TECHNOLOGY, ISSN 2190-9385, Vol. 7, nr 4, s. 409-415Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

This study investigates the influence of temperature, salt concentration and thickness on the corrosion resistance of seven YSZ thermal barrier coatings in the presence of V2O5 and Na2SO4. For this study, a thick, high-porosity APS coating (670 gm) using hollow spherical powder (HOSP) and a thin, low-porosity APS coating (300 pm) using agglomerated and sintered (Aamp;S) powder were fabricated. Corrosion tests were conducted at 750 degrees C and 900 degrees C with a mixture of Na2SO4 and V2O5 for four hours. At each temperature, salt concentrations of 4,10 and 20 mg/cm(2) were used. SEM and XRD investigations after the corrosion tests revealed that a combination of low temperature and high salt concentration resulted in higher corrosion-induced damage to the thin TBC coatings. With regard to the thick TBC coatings, all except one sample failed during the corrosion test. This suggests that thick TBC coatings with higher porosity may not be suitable in corrosive environments.

##### Ort, förlag, år, upplaga, sidor
GOLLER VERLAG GMBH, 2016
##### Nyckelord
HOSP; agglomerated and sintered YSZ; hot corrosion; TBC
Materialkemi
##### Identifikatorer
urn:nbn:se:liu:diva-134310 (URN)10.4416/JCST2016-00058 (DOI)000391246300013 ()
##### Anmärkning

Funding Agencies|Vinnova, Sweden

4. A study of damage evolution in high purity nano TBCs during thermal cycling: A fracture mechanics based modelling approach
Öppna denna publikation i ny flik eller fönster >>A study of damage evolution in high purity nano TBCs during thermal cycling: A fracture mechanics based modelling approach
2017 (Engelska)Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, nr 8, s. 2889-2899Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

This work concerns the study of damage evolution in a newly developed high purity nano 8YSZ thermal barrier coating during thermal cyclic fatigue tests (TCF). TCF tests were conducted between 100 degrees C-1100 degrees C with a hold time of 1 hat 1100 degrees C, first till failure and later for interrupted tests. Cross section analysis along the diameter of the interrupted test samples revealed a mixed-type failure and that the most of the damage occurred towards the end of the coatings life. To understand the most likely crack growth mechanism leading to failure, different crack growth paths have been modelled using finite element analysis. Crack growing from an existing defect in the top coat towards the top coat/TGO interface has been identified as the most likely mechanism. Estimated damage by the model could predict the rapid increase in the damage towards the end of the coatings life. (C) 2017 Elsevier Ltd. All rights reserved.

##### Ort, förlag, år, upplaga, sidor
ELSEVIER SCI LTD, 2017
##### Nyckelord
Thermal cyclic fatigue; High purity nano YSZ; Crack growth modelling; Damage evolution
Materialkemi
##### Identifikatorer
urn:nbn:se:liu:diva-137827 (URN)10.1016/j.jeurceramsoc.2017.02.054 (DOI)000400531500015 ()
##### Anmärkning

Funding Agencies|Vinnova in Sweden

5. Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating
Öppna denna publikation i ny flik eller fönster >>Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating
2017 (Engelska)Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 332, s. 47-56Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Thermal barrier coatings (TBCs), consisting of a ceramic top coat and a metallic bond coat, offer resistance against high temperature degradation of turbine components. Cyclic oxidation of the bond coat, thermal stresses due to their thermal mismatches during cyclic operations, and sintering of the top coat are considered to be the common ways by which thermal barrier coatings fail. To reduce sintering, a nano structured high purity yttria stabilized zirconia (YSZ) was developed. The focus of this work is to compare the damage development of such high purity nano YSZ TBC during thermal cycling with a conventional YSZ TBC. Thermal cyclic fatigue (TCF) tests were conducted on both the TBC systems between 100 °C and 1100 °C with a 1 h hold time at 1100 °C. TCF test results showed that conventional YSZ TBC exhibited much higher life compared to the high purity nano YSZ TBC. The difference in the lifetime is explained by the use of microstructural investigations, crack length measurements along the cross-section and the difference in the elastic modulus. Furthermore, stress intensity factors were calculated in order to understand the difference(s) in the damage development between the two TBC systems.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2017
##### Nyckelord
High purity nano, damage evolution, thermal cycling fatigue, crack length measurement, conventional TBC
##### Nationell ämneskategori
Materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-142311 (URN)10.1016/j.surfcoat.2017.09.069 (DOI)000418968100007 ()2-s2.0-85030751243 (Scopus ID)
##### Anmärkning

Funding agencies: Vinnova in Sweden [2015-06870]

6. Thermal barrier coatings: Life model development and validation
Öppna denna publikation i ny flik eller fönster >>Thermal barrier coatings: Life model development and validation
2019 (Engelska)Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 362, s. 293-301Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The failure of thermal barrier coatings (TBCs) during thermal cyclic fatigue (TCF) tests depends mainly on the thermal mismatch between the coating and the substrate, the thermally grown oxides (TGO) at the top coat-bond coat interface, and the sintering of the top coat. Understanding the interplay between these factors is essential for developing a life model. The present work focuses on further development of a previously established fracture mechanics based life model and its validation by comparing with the experimental results. The life model makes use of a Paris' law type equation to estimate the cycles to failure based on micro-crack growth. The fitting parameters for the Paris' law were obtained from the experimentally measured crack lengths after the interruption of TCF tests at different cycles. An alternative approach to obtain the fitting parameters through video monitoring was also discussed. It is shown that regardless of the approach to obtain the fitting parameters, the life model in its current form is able to predict the TCF life at different temperatures with reasonable accuracy. However, at very high temperatures (1150 °C) the predictive capabilities of the model appeared to be poor.

##### Nyckelord
Thermal barrier coatings, Thermal cyclic fatigue, Life modeling, Life prediction
##### Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
##### Identifikatorer
urn:nbn:se:liu:diva-154779 (URN)10.1016/j.surfcoat.2019.01.117 (DOI)000461526400035 ()
##### Anmärkning

Funding agencies: VINNOVA in Sweden

7. Fatigue life prediction of thermal barrier coatings using a simplified crack growth model
Öppna denna publikation i ny flik eller fönster >>Fatigue life prediction of thermal barrier coatings using a simplified crack growth model
2019 (Engelska)Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, nr 5, s. 1869-1876Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Models that can predict the life of thermal barrier coatings (TBCs) during thermal cycling fatigue (TCF) tests are highly desirable. The present work focuses on developing and validating a simplified model based on the relation between the energy release rate and the TCF cycles to failure. The model accounts for stresses due to thermal mismatch, influence of sintering, and the growth of TGO (alumina and other non-protective oxides). The experimental investigation of TBCs included; 1) TCF tests at maximum temperatures of 1050 °C, 1100 °C, 1150 °C and a minimum temperature of 100 °C with 1 h and 5 h (1100 °C) hold times. 2) Isothermal oxidation tests at 900, 1000 and 1100 °C for times up to 8000 h. The model was calibrated and validated with the experimental results. It has been shown that the model is able to predict the TCF life and effect of hold time with good accuracy.

##### Nyckelord
Thermal barrier coatings, Thermal cycling fatigue, Life prediction model, Energy release rate
##### Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
##### Identifikatorer
urn:nbn:se:liu:diva-154780 (URN)10.1016/j.jeurceramsoc.2018.12.046 (DOI)000459950700016 ()
##### Anmärkning

Funding agencies: Vinnova in Sweden

• 35.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska fakulteten.
Influence of deformation and environmental degradation of Inconel 7922017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)

Industrial gas turbines are often used as a mechanical drive for pumps and compressors or in power generation as an electric power supply. The gas turbine has for many years been a popular engine due to its flexibility with respect to different types of fuel and due to a design, that enables a high power-to-weight ratio. A simplified description of a gas turbine is that the engine consists of a cold and hot section. The turbo compressor section belongs to cold section and the combustion chamber together with the turbine section belongs to the hot section. In the hot section of a gas turbine, the condition is extremely severe because of an aggressive environment characterized by high temperatures, increased temperature gradients, high pressure and centrifugal forces resulting in large stresses on individual components together with an oxidizing and corroding atmosphere. Materials used in the high temperature section (hot gas path) of a modern gas turbine are different types of superalloys, as single crystal, directionally solidified or polycrystalline alloys, depending on temperature and load conditions. In the first turbine stage, temperature is very high due to exposure to the combustion gas. To handle the problem with creep, single crystal superalloys are often used in this section. In the second row of turbine blades, the temperature of the gas is lower and polycrystalline superalloys are typically used. IN-792 is a cast polycrystalline superalloy with high strength, good resistance to hot corrosion and a cheaper option than single crystals. In the hot section of gas turbine, IN-792 is a suitable material for components such as turbine blades and vans where a complex load condition, high temperature and severe environment prevails. Due to startup and shutdown of the gas turbine engine during service, the components in the hot section are exposed to cyclic load and temperature. This will generate mechanical and thermal fatigue damage in gas turbine components. Steady state temperature gradient arises by the cooling system acting at cold spots during service to introduce tensile stress, which indirectly gives rise to creep damage in the component. This work includes tree studies of deformation and damage mechanisms of superalloy IN-792. The first study is made on test bars exposed to thermomechanical fatigue in laboratory environment, the second and the third study is made on turbine blades used during service. In the second study, the machines are placed off-shore and exposed to marine environment. In the third study the machine is landbased and exposed to an industrial environment. In the second study, the deformation and damage mechanisms are compared between the turbine blades used during service and the test bars exposed to thermomechanical fatigue testing in the first study.

1. Deformation and damage mechanisms in IN792 during thermomechanical fatigue
Öppna denna publikation i ny flik eller fönster >>Deformation and damage mechanisms in IN792 during thermomechanical fatigue
2011 (Engelska)Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, nr 13-14, s. 4658-4668Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystallinesuperalloy IN792 have been investigated. The TMF cycles used in this study are in-phase(IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 ◦C while the maximumtemperature is 500 or 750 ◦C in the IP TMF-tests and 750, 850 or 950 ◦C in the OP TMF-tests. Themajority of the cracks are transcrystalline, except for the IP TMF-test at 750 ◦C, where some tendencyto intercrystalline crack growth can be seen. In all tests, the cracks were initiated and propagated inlocations where deformation structures such as deformation bands have formed in the material. In thetemperature interval 750–850 ◦C, twins were formed in both IP and OP TMF-tests and this behaviouris observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observedfor tests with a lower (500 ◦C) and a higher (950 ◦C) maximum temperature. Recrystallization at grainboundaries, around particles and within the deformation structures have occurred in the OP TMF-testswith a maximum temperature of 850 and 950 ◦C and this is more apparent for the higher temperature.Void formation is frequently observed in the recrystallized areas even for the case of compressive stressesat high temperature.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2011
##### Nyckelord
Nickel based superalloys, Fatigue, Shear bands, Recrystallization, Twinning
##### Nationell ämneskategori
Teknik och teknologier Annan materialteknik
##### Identifikatorer
urn:nbn:se:liu:diva-67259 (URN)10.1016/j.msea.2011.02.063 (DOI)000290004200051 ()
##### Anmärkning
Original Publication: Jan Kanesund, Johan Moverare and Sten Johansson, Deformation and damage mechanisms in IN792 during thermomechanical fatigue, 2011, Materials Science & Engineering: A, (528), 13-14, 4658-4668. http://dx.doi.org/10.1016/j.msea.2011.02.063 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Tillgänglig från: 2011-04-06 Skapad: 2011-04-06 Senast uppdaterad: 2017-12-11
• 36.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system.
Termomekanisk utmattning av Sanicro 25: Materialmodellering med finita elementmetoden2014Självständigt arbete på grundnivå (kandidatexamen), 10,5 poäng / 16 hpStudentuppsats (Examensarbete)

The report aims to describe the austenitic stainless steel Sanicro 25 from a thermomechanical point of view. The thermal and mechanical properties of the material make it suitable for use in coal – and thermal power plants. By the use of Sanicro 25 it would be possible to bring the efficiency of these plants up while bringing the carbon emissions down.A material model is created from material testing and validated through simulation in the finite element software Abaqus. The model that has been derived describes the material behavior during loading and stress relaxation for the first cycle in a thermomechanical fatigue test well. The unloading part of the cycle however cannot be described correctly by the use of this model.

• 37.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten. Sungkyunkwan University, South Korea; Sungkyunkwan University, South Korea. Soochow University, Peoples R China; Soochow University, Peoples R China; IFW Dresden, Germany; Polish Academic Science, Poland. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
Graphene on graphene formation from PMMA residues during annealing2017Ingår i: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 137, s. 191-194Artikel i tidskrift (Refereegranskat)

PMMA is a common support material for transferring graphene between substrates. However, PMMA residues typically remain on the graphene sheet after the transfer process. A high temperature annealing process is commonly applied to reduce the amount of PMMA residues. It is also known that high temperature annealing of PMMA causes the PMMA to graphitize, which has been used as a method to synthesize graphene on metal substrates. In this letter we show the development of additional graphene layers during high temperature annealing, which occurs on a single, clean, graphene sheet. The additional graphene is nucleated from the decomposition products of PMMA residues. (C) 2017 Elsevier Ltd. All rights reserved.

• 38.
Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
Diffuse Liver Disease: Measurements of Liver Trace Metal Concentrations and R2* Relaxation Rates2016Konferensbidrag (Refereegranskat)

Introduction

Over the past decade, several methods for measuring of liver iron content (LIC) non-invasively with MRI have been developed and verified. The most promising methods uses relaxometry, measuring either R2- or R2* relaxation rate in the liver1,2. For instance, several studies have shown that there seems to be a linear relationship between R2* and LIC1. However, few of these studies have measured the liver content of other metals, which could also affect the relaxation rates. The goal of this study was to investigate if any trace metals, other than iron could affect the R2* relaxation rate in liver tissue in a patients with diffuse liver disease.

Subjects and methods

75 patients with suspected diffuse liver disease underwent an MRI examination followed by a liver biopsy the same day. The R2* relaxation rate of the water protons in the liver was measured using an axial 3D multi-slice fat-saturated multi-echo turbo field echo sequence (TE=4.60/9.20/13.80/18.40/23.00ms). Regions of interest (ROI) were drawn and R2* was estimated by fitting the mean signal intensity from the ROIs to a mono-exponential decay model. The biopsies were freeze dried and the concentrations of iron, manganese, copper, cobalt and gadolinium were measured using Inductively Coupled Plasma Sector Field Mass Spectrometry (ICP-SFMS). A multiple linear regression analysis was applied to determine which of the measured metals significantly affected the relaxation rate.

Results

A linear regression with the LIC and R2* showed a reasonable fit (Figure 1). The multiple linear regression analysis (Table 1) showed that iron as well as manganese had a significant affect on R2*. Unlike iron however, the regression coefficient of manganese was negative, meaning that an increasing manganese concentration gave a shorter R2* relaxation rate. The same trend can be seen when plotting the manganese concentration against R2* (Figure 2).

• 39.
NUST MISIS, Russia.
Lomonosov Moscow State Univ, Russia. Hampton Thermodynam Ltd, England. Lomonosov Moscow State Univ, Russia. NUST MISIS, Russia. Lomonosov Moscow State Univ, Russia. NUST MISIS, Russia. NUST MISIS, Russia. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. NUST MISIS, Russia.
Thermodynamic properties of tin: Part I Experimental investigation, ab-initio modelling of alpha-, beta-phase and a thermodynamic description for pure metal in solid and liquid state from 0 K2019Ingår i: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 65, s. 50-72Artikel i tidskrift (Refereegranskat)

Thermodynamic data for crystalline white and grey tin were assessed using an extended Einstein model from 0 K. Ab-initio simulations in the framework of density functional theory (DFT) with the quasiharmonic approximation (QHA) were carried out to define the heat capacities for both phases of tin from 0 K up to room temperatures. Good agreement was observed between theoretical and experimental heat capacities, which makes it possible to combine theoretical and experimental data to determine the standard entropies. Data for the liquid phase were described using a two state model. During the assessment, careful analysis of the experimental data was carried out. In order to fulfil the need for a precise evaluation of S-298(o) we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point and to estimate solid phase transition entropy and enthalpy which are difficult to measure due to a high activation barrier. Additional measurements of heat capacity were carried out where existing data were scarce.

Publikationen är tillgänglig i fulltext från 2021-02-16 11:17
• 40.
Max Planck Inst Eisenforsch GmbH, Germany.
Max Planck Inst Eisenforsch GmbH, Germany. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Univ Oxford, England. Max Planck Inst Eisenforsch GmbH, Germany. Max Planck Inst Eisenforsch GmbH, Germany.
The Role of Oxidized Carbides on Thermal-Mechanical Performance of Polycrystalline Superalloys2018Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, nr 9, s. 4236-4245Artikel i tidskrift (Refereegranskat)

Oxidized MC carbides which act as main crack initiation sites in a polycrystalline superalloy under thermal-mechanical fatigue (TMF) conditions at 850 degrees C were studied. Microstructural observations in the TMF tested specimens were compared to findings from bulk samples exposed isothermally in air at 850 degrees C for 30 hours in the absence of any external applied load. Carbides were found to oxidize rapidly after exposure at 850 degrees C for 30 hours resulting in surface eruptions corresponding to oxidation products, from where micro-cracks initiated. Plastic deformation due to volume expansion of the often porous oxidized carbides led to high dislocation densities in the adjacent matrix as revealed by controlled electron channeling contrast imaging. The high dislocation density facilitated the dissolution kinetics of gamma precipitates by segregation and diffusion of chromium and cobalt along the dislocations via pipe diffusion, resulting in the formation of soft recrystallized grains. Atom probe tomography revealed substantial compositional differences between the recrystallized grains and the adjacent undeformed gamma matrix. Similar observations were made for the TMF tested alloy. Our observations provide new insights into the true detrimental role of oxidized MC carbides on the crack initiation performance of polycrystalline superalloys under TMF.

• 41.
Univ West, Sweden.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Chalmers Univ Technol, Sweden. NTNU, Norway. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Univ West, Sweden. Univ West, Sweden.
Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling2019Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, nr 5, s. 2527-2537Artikel i tidskrift (Refereegranskat)

Electron beam melting (EBM) is a powder bed additive manufacturing process where a powder material is melted selectively in a layer-by-layer approach using an electron beam. EBM has some unique features during the manufacture of components with high-performance superalloys that are commonly used in gas turbines such as Alloy 718. EBM has a high deposition rate due to its high beam energy and speed, comparatively low residual stresses, and limited problems with oxidation. However, due to the layer-by-layer melting approach and high powder bed temperature, the as-built EBM Alloy 718 exhibits a microstructural gradient starting from the top of the sample. In this study, we conducted modeling to obtain a deeper understanding of microstructural development during EBM and the homogenization that occurs during manufacturing with Alloy 718. A multicomponent phase-field modeling approach was combined with transformation kinetic modeling to predict the microstructural gradient and the results were compared with experimental observations. In particular, we investigated the segregation of elements during solidification and the subsequent in situ homogenization heat treatment at the elevated powder bed temperature. The predicted elemental composition was then used for thermodynamic modeling to predict the changes in the continuous cooling transformation and time-temperature transformation diagrams for Alloy 718, which helped to explain the observed phase evolution within the microstructure. The results indicate that the proposed approach can be employed as a valuable tool for understanding processes and for process development, including post-heat treatments. (C) The Author(s) 2019

• 42.
Univ West, Sweden.
GKN Aerosp Engine Syst AB, Sweden. Chalmers Univ Technol, Sweden. Univ West, Sweden. Univ West, Sweden. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Univ West, Sweden. Univ West, Sweden.
Microstructure modelling of laser metal powder directed energy deposition of alloy 7182019Ingår i: ADDITIVE MANUFACTURING, ISSN 2214-8604, Vol. 25, s. 357-364Artikel i tidskrift (Refereegranskat)

A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and delta phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.

• 43.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
Physical vapor deposition and thermal stability of hard oxide coatings2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

The state-of-the-art tools for machining metals are primarily based on a metal-ceramic composite (WC-Co) coated with different combinations of carbide, nitride, and oxide coatings. Combinations of these coating materials are optimized to withstand specific wear conditions. Oxide coatings, mainly α-Al2O3, are especially desired because of their high hot-hardness, chemical inertness with respect to the workpiece, and their low friction. The search for possible alloy elements, which may facilitate the deposition of such oxides by means of physical vapor deposition (PVD) techniques, has been the goal of this thesis. The sought alloy should form thermodynamically stable or metastable compounds, compatible with the temperature of use in metal cutting application. This thesis deals with process development and coating characterization of such new oxide alloy thin films, focusing on the Al-V-O, Al-Cr-Si-O, and Cr-Zr-O systems.

Alloying aluminum oxide with iso-valent vanadium is a candidate for forming the desired alloys. Therefore, coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited with reactive sputter deposition. X-ray diffraction showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, (63 - 42 at.% V), and a gamma-alumina-like solid solution at lower V-content, (18 and 7 at.%), were observed, the later was shifted to larger d-spacing compared to the pure γ-Al2O3 sample obtained if deposited with only Al-target. Annealing the Al-rich coatings in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating which transformed to α-Al2O3 after annealing to 1100° C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The hardness then decreases with increasing V-content, larger than 7 at.% V metal fraction. Doping the Al2O3 coating with 7 at.% V resulted in a significant surface smoothening compared to the binary oxide. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings. This work increases the understanding of this complicated material system with respect to possible phases formed with pulsed DC magnetron sputtering deposition as well as their response to annealing in air.

The inherent difficulties of depositing insulating oxide films with PVD, requiring a closed electrical circuit, makes the investigation of process stability an important part of this research. In this context, I investigated the influence of adding small amount of Si in Al-Cr cathode on the coating properties in a pulsed DC industrial cathodic arc system and the plasma characteristics, process parameters, and coating properties in a lab DC cathodic arc system. Si was chosen here due to a previous study showing improved erosion behavior of Al-Cr-Si over pure Al-Cr cathode without Si incorporation in the coating. The effect of Si in the Al-Cr cathode in the industrial cathodic arc system showed slight improvements on the cathode erosion but Si was found in all coatings where Si was added in the cathode. The Si addition promoted the formation of the B1-like metastable cubic oxide phase and the incorporation led to reduced or equal hardness values compared to the corresponding Si-free processes. The DC-arc plasma study on the same material system showed only small improvements in the cathode erosion and process stability (lower pressure and cathode voltage) when introducing 5 at.% Si in the Al70Cr30-cathode. The presence of volatile SiO species could be confirmed through plasma analysis, but the loss of Si through these species was negligible, since the coating composition matched the cathode composition also under these conditions. The positive effect of added Si on the process stability at the cathode surface, should be weighed against Si incorporation in the coating. This incorporation seems to lead to a reduction in mechanical properties in the as-deposited coatings and promote the formation of a B1-like cubic metastable oxide structure for the (Al,Cr)2O3 oxide. This formation may or may not be beneficial for the final application since literature indicates a slight stabilization of the metastable phase upon Si-incorporation, contrary to the effect of Cr, which stabilizes the α-phase.

The thermal stability of alloys for metal cutting application is crucial for their use. Previous studies on another alloy system, Cr-Zr-O, had shown solid solution, for Cr-rich compositions in that material system, in the sought corundum structure. The thermal stability of α-Cr0.28Zr0.10O0.61 coating deposited by reactive radio frequency (RF)-magnetron sputtering at 500 °C was therefore investigated here after annealing in vacuum up to 870 °C. The annealed samples showed transformation of α-(Cr,Zr)2O3 and amorphous ZrOx-rich areas into tetragonal ZrO2 and bcc-Cr. The instability of the α-(Cr,Zr)2O3 is surprising and possibly related to the annealing being done under vacuum, facilitating the loss of oxygen. Further in situ synchrotron XRD annealing studies on the α-Cr0.28Zr0.10O0.61 coating in air and in vacuum showed increased stability for the air annealed sample up to at least 975 °C, accompanied with a slight increase in ex-situ measured nanohardness. The onset temperature for formation of tetragonal ZrO2 was similar to that for isothermally vacuum annealing. The synchrotron-vacuum annealed coating again decomposed into bcc-Cr and t-ZrO2, with an addition of monoclinic–ZrO2 due to grain growth. The stabilization of the room temperature metastable tetragonal ZrO2 phase, due to surface energy effects present with small grains sizes, may prove to be useful for metal cutting applications. The observed phase segregation of α-(Cr,Zr)2O3 and formation of tetragonal ZrO2 with corresponding increase in hardness for this pseudobinary oxide system also opens up design routes for pseudobinary oxides with tunable microstructural and mechanical properties.

1. Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings
Öppna denna publikation i ny flik eller fönster >>Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings
2019 (Engelska)Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, artikel-id 137369Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.

##### Ort, förlag, år, upplaga, sidor
Elsevier, 2019
##### Nyckelord
Aluminum vanadium oxide Pulsed DC magnetron sputtering Annealing V2O5 AlVO4 AlVO3
Fysik
##### Identifikatorer
urn:nbn:se:liu:diva-159749 (URN)10.1016/j.tsf.2019.06.019 (DOI)000485256500035 ()
2. Effect of Si on DC arc plasma generation from Al-Cr and Al-Cr-Si cathodes used in oxygen
Öppna denna publikation i ny flik eller fönster >>Effect of Si on DC arc plasma generation from Al-Cr and Al-Cr-Si cathodes used in oxygen
2017 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, nr 8, artikel-id 083303Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Al2O3 alloyed with Cr is an important material for the tooling industry. It can be synthesized from an arc discharge using Al-Cr cathodes in an oxygen atmosphere. Due to formation of Al-rich oxide islands on the cathode surface, the arc process stability is highly sensitive to oxygen pressure. For improved stability, the use of Al0.70Cr0.25Si0.05 cathodes has previously been suggested, where Si may reduce island formation. Here, we have investigated the effect of Si by comparing plasma generation and thin film deposition from Al0.7Cr0.3 and Al0.7Cr0.25Si0.05 cathodes. Plasma ion composition, ion energies, ion charge states, neutral species, droplet formation, and film composition have been characterized at different O-2 flow rates for arc currents of 60 and 90 A. Si and related compounds are detected in plasma ions and in plasma neutrals. Scanning electron microscopy and energy dispersive X-ray analysis show that the cathode composition and the film composition are the same, with Si present in droplets as well. The effect of Si on the process stability, ion energies, and ion charge states is found to be negligible compared to that of the arc current. The latter is identified as the most relevant parameter for tuning the properties of the reactive discharge. The present work increases the fundamental understanding of plasma generation in a reactive atmosphere, and provides input for the choice of cathode composition and process parameters in reactive DC arc synthesis.

##### Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2017
##### Nationell ämneskategori
Oorganisk kemi
##### Identifikatorer
urn:nbn:se:liu:diva-136304 (URN)10.1063/1.4976862 (DOI)000395289400006 ()
##### Anmärkning

Funding Agencies|Swedish Research Council [621212-4368]; Knut and Alice Wallenberg ( KAW) Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]

3. Structural evolution in reactive RF magnetron sputtered (Cr,Zr)2O3 coatings during annealing
Öppna denna publikation i ny flik eller fönster >>Structural evolution in reactive RF magnetron sputtered (Cr,Zr)2O3 coatings during annealing
2017 (Engelska)Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 131, s. 543-552Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Reactive RF-magnetron sputtering is used to grow Cr0.28Zr0.10O0.61 coatings at 500 degrees C. Coatings are annealed at 750 degrees C, 810 degrees C, and 870 degrees C. The microstructure evolution of the pseudobinary oxide compound is characterized through high resolution state of the art HRSTEM and HREDX-maps, revealing the segregation of Cr and Zr on the nm scale. The as-deposited coating comprises cc-(Cr,Zr)(2)O-3 solid solution with a Zr-rich (Zr,Cr)O-x. amorphous phase. After annealing to 750 degrees C tetragonal ZrO2 nucleates and grows from the amorphous phase. The ZrO2 phase is stabilized in its tetragonal structure at these fairly low annealing temperatures, possibly due to the small grain size (below 30 nm). Correlated with the nucleation and growth of the tetragonal-ZrO2 phase is an increase in hardness, with a maximum hardness after annealing to 750 degrees C, followed by a decrease in hardness upon coarsening, bcc metallic Cr phase formation and loss of oxygen, during annealing to 870 degrees C. The observed phase segregation opens up future design routes for pseudobinary oxides with tunable microstructural and mechanical properties. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

##### Ort, förlag, år, upplaga, sidor
PERGAMON-ELSEVIER SCIENCE LTD, 2017
##### Nyckelord
Chromium zirconium oxide; Eskolaite; RF magnetron sputtering; Annealing; TEM
Materialkemi
##### Identifikatorer
urn:nbn:se:liu:diva-138476 (URN)10.1016/j.actamat.2017.03.063 (DOI)000402343400051 ()
##### Anmärkning

Funding Agencies|Swedish Research Council (VR) [621-212-4368, 330-2014-6336]; AB Sandvik Coromant; Karlsruhe Nano Micro Facility (KNMF); Helmholtz research infrastructure at Karlsruhe Institute of Technology (KIT); Marie Sklodowska Curie Actions, Cofund [INCA 600398]; Knut and Alice Wallenberg Foundation