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  • 1.
    Aghda, Soheil Karimi
    et al.
    Rhein Westfal TH Aachen, Germany.
    Bogdanovski, Dimitri
    Rhein Westfal TH Aachen, Germany.
    Lo, Lukas
    Sua, Heng Han
    Rhein Westfal TH Aachen, Germany.
    Patterer, Lena
    Rhein Westfal TH Aachen, Germany.
    Holzapfel, Damian M.
    Rhein Westfal TH Aachen, Germany.
    Le Febvrier, Arnaud
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hans, Marcus
    Rhein Westfal TH Aachen, Germany.
    Primetzhofer, Daniel
    Uppsala Univ, Sweden.
    Schneider, Jochen M.
    Rhein Westfal TH Aachen, Germany.
    Valence electron concentration- and N vacancy-induced elasticity in cubic early transition metal nitrides2023In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 255, article id 119078Article in journal (Refereed)
    Abstract [en]

    Motivated by frequently reported deviations from stoichiometry in cubic transition metal nitride (TMNx) thin films, the effect of N-vacancy concentration on the elastic properties of cubic TiNx, ZrNx, VNx, NbNx, and MoNx (0.72 & LE; x & LE; 1.00) is systematically studied by density functional theory (DFT) calculations. The predictions are validated experimentally for VNx (0.77 & LE; x & LE; 0.97). The DFT results indicate that the elastic behavior of the TMNx depends on both the N-vacancy concentration and the valence electron concentration (VEC) of the transition metal: While TiNx and ZrNx exhibit vacancy-induced reductions in elastic modulus, VNx and NbNx show an increase. These trends can be rationalized by considering vacancy-induced changes in elastic anisotropy and bonding. While introduction of N-vacancies in TiNx results in a significant reduction of elastic modulus along all directions and a lower average bond strength of Ti-N, the vacancy-induced reduction in [001] direction of VNx is overcompensated by the higher stiffness along [011] and [111] directions, resulting in a higher average bond strength of V-N. To validate the predicted vacancy-induced changes in elasticity experimentally, close-to-singlecrystal VNx (0.77 & LE; x & LE; 0.97) are grown on MgO(001) substrates. As the N-content is reduced, the relaxed lattice parameter a0, as probed by X-ray diffraction, decreases from 4.128 & ANGS; to 4.096 & ANGS;. This reduction in lattice parameter is accompanied by an anomalous 11% increase in elastic modulus, as determined by nanoindentation. As the experimental data agree with the predictions, the elasticity enhancement in VNx upon N-vacancy formation can be understood based on the concomitant changes in elastic anisotropy and bonding.

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  • 2.
    Aid, Graham
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Environmental Technology and Management. Ragn-sells, Sweden.
    Kihl, Anders
    Ragn Sells AB.
    Driving forces and inhibitors of secondary stock extraction2014Conference paper (Other academic)
    Abstract [en]

    Even though it’s well known to mankind that our common resources are limited and that recycling is a key for a sustainable future; in reality we see few examples of true recycling where virgin raw material is substituted by waste. There are endless number of examples where waste is utilized to some extent without solving the core issue: reducing the need of extracting virgin raw materials. This article analyses some of the driving forces and inhibitors that explains why it’s so difficult establish secondary stock extraction although technology is available. The authors discuss and suggest possible ways for reducing the some of the main barriers.

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  • 3.
    Albertini, Gianni
    et al.
    Dipartimento di Scienze dei Materiali e della Terra, Universita, Ancona, Italy.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Manescu, Adrian
    Instituto di Scienze Fisiche, Universita, Ancona, Italy.
    Ponzetti, Araldo
    NUOVA M.A.I.P SpA, Viale Cavalotti n 30, Jesi, Italy.
    Neutron Diffraction Measurement of Residual Stress in a centrifugal Bowl of Duplex Steel2001In: Journal of Neutron Research, ISSN 1023-8166, E-ISSN 1477-2655, Vol. 9, p. 305-312Article in journal (Refereed)
  • 4.
    Andersen Söderbergh, Kim
    Linköping University, Department of Management and Engineering, Carl Malmsten - furniture studies. Linköping University, The Institute of Technology.
    Blästring av trä: Ett materialbibliotek av blästrade och ytbehandladeträytor2012Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    In my thesis I have sand blasted different type of woods - ring-porous and diffuseporous deciduous tree species and conifers - to show different results depending on the species, the direction of the grain and the effects of surface treatment of a blasted surface.

    The results of my tests were sometimes unexpected, such as that the sand from blasting almost completely disappeared, that all wood surfaces after blasting exhibited a much lighter or paler surface than before and that the diffuse-porous tree species showed differences in hardness between the beginning and end of annual rings.

    By creating a library of different kinds of wood and sandblasted surface treatment, I have created a reference bank that I will be able to use me in the manufacturing of interiors, furniture and other objects.

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    Blästring av trä
  • 5.
    Andersson, Elise
    et al.
    Möbelkonservator på Nationalmuseum, styrelsemedlem i Malmstens Alumni.
    Brunne, UlfOrdförande i Malmstens Alumni, snickarmästare och möbelkonservator f.d. studierektor på Malmstens (LiU).Helgesson, RobinAnställd på Spågan möbelkonserevring AB, styrelsemedlem i Malmstens Alumni, möbelsnickare och möbelkonservator .Vaher, LauriLinköping University, Department of Management and Engineering, Malmstens Linköping University. Linköping University, Faculty of Science & Engineering.
    Proceedings of the symposium Woodworking Tools and Techniques – Past, Present and Future, Stockholm 16-19 September 20222023Conference proceedings (editor) (Other academic)
    Abstract [en]

    The 3rd Swedish Symposium on Furniture Technology& Design was held in Stockholm the 16th through the19th of September 2022, this time arranged by MalmstensAlumni in collaboration with the Swedish History Museum,Skokloster Castle and LiU Malmstens.

    Contents:

    Foreword page 6Ulf Brunne, Chairman, Malmstens Alumni

    Woodworking Tools and Techniques – Technical and Aesthetical Aspects of Furniture Design and Cabinetmaking through the Ages page 7Johan Knutsson, Professor in Furniture Culture LiU Malmstens, Sweden

    From Tool Marks to Work Practises page 14Hans Piena, Curator of Domestic Culture, Dutch Open Air Museum, The Netherlands

    Characteristics of Japanese Woodworking Tools page 21Kenji Komatsu, Woodworker/Artist, Wood Workshop BYHAND, Japan

    A Reconstruction of an Early 16th Century Tondo Frame page 29Iskander Breebaart, Senior Furniture Conservator Rijksmuseum, The Netherlands

    Wave Mouldings and Ornamental Lathe page 37Josephine Erckrath, Cabinetmaker and Furniture Conservator Møbelarkitekt Tyge Axel Holm, Denmark

    Dutch Moulding Planes from Skokloster Castle, Sweden page 42Jaap Boonstra, Furniture Conservator, Amsterdam Museum, The Netherlands, Pol Bruijs, Furniture Conservator, Private Practise, The Netherlands

    Mahogany Spheres – Reconstruction of an Artistically Crafted Element of a Writing Cabinet by the Berlin Ebenist Joseph Schneevogl (1795–1864) page 54Prof. Dr. Angelika Rauch, University of Applied Sciences, Potsdam, GermanyDipl.-Rest. Jörg Weber, Head of Workshop, University of Applied Sciences Potsdam, Germany

    Construction Features that are Typical for Marquetry Cabinets by Jan van Mekeren page 60Paul van Duin, Head of Furniture Conservation, Rijksmuseum, The NetherlandsIskander Breebaart, Senior Furniture Conservator, Rijksmuseum, The Netherlands

    Australian Timbers and Contemporary Woodworking page 68Evan Dunstone, Dunstone Design, Australia

    Woodworking as Means for Understanding and Developing the Human-Technology Relationship – Discussed Through the Work of Cabinet Maker Thomas Tempte page 74Andreas Nobel, Professor in Furniture Design LiU Malmstens, Sweden

    The Future of Furniture Craft Education – a Churchill Fellowship page 80Joseph Bray, Head of Wood School Sylva Foundation, UK

    Applied Information Technology and Mathematics in Woodturning page 86Ulf Jansson, Engineer and Woodturner Private Practise, Sweden

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  • 6.
    Andersson, Mike
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
    Technology and application opportunities for SiC-FET gas sensors2012In: Solid State Gas Sensors - Industrial Application / [ed] Maximilian Fleischer and Mirko Lehmann, Springer Berlin/Heidelberg, 2012, p. 189-214Chapter in book (Refereed)
    Abstract [en]

    The development of SiC-FET gas sensors has proceeded for about fifteen years. The maturity of the SiC material and a deeper understanding of the transduction mechanisms and sensor surface processes behind the sensitivity to a number of target substances have recently allowed the development of market-ready sensors for certain applications. Some examples presented below are a sensor system for domestic boiler control, an ammonia sensor for control of the SCR (selective catalytic reduction) and SNCR (Selective Non-Catalytic Reduction) NOx abatement processes as well as other more or less market-ready applications. In parallel, the basic research continues in order to reach more demanding markets/new applications and also to possibly lower the production costs of the sensors. Therefore, current research and future challenges are also treated, such as the development of new types of conducting ceramics for ohmic contacts to SiC in order to increase the operation temperature beyond the present state of the art.

  • 7.
    Arbring Sjöström, Theresia
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Jonsson, Amanda
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Stanford University, CA 94305 USA.
    Gabrielsson, Erik
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Kergoat, Loig
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Aix Marseille University, France.
    Tybrandt, Klas
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Berggren, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Simon, Daniel
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Cross-Linked Polyelectrolyte for Improved Selectivity and Processability of lontronic Systems2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 36, p. 30247-30252Article in journal (Refereed)
    Abstract [en]

    On-demand local release of biomolecules enables fine-tuned stimulation for the next generation of neuromodulation therapies. Such chemical stimulation is achievable using iontronic devices based on microfabricated, highly selective ion exchange membranes (IEMs). Current limitations in processability and performance of thin film LEMs hamper future developments of this technology. Here we address this limitation by developing a cationic IEM with excellent processability and ionic selectivity: poly(4-styrenesulfonic acidco-maleic acid) (PSS-co-MA) cross-linked with polyethylene glycol (PEG). This enables new design opportunities and provides enhanced compatibility with in vitro cell studies. PSSA-co-MA/PEG is shown to out-perform the cation selectivity of the previously used iontronic material.

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  • 8. Order onlineBuy this publication >>
    Armakavicius, Nerijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Study of novel electronic materials by mid-infrared and terahertz optical Hall effect2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Development of silicon based electronics have revolutionized our every day life during the last three decades. Nowadays Si based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, Si cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for a progress in state of the art electronics.

    Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in the current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported. Thus, a good understanding of the intrinsic free charge carriers properties and the factors affecting them is very important for further development of epitaxial graphene.

    III-group nitrides have been extensively studied and already have proven their high efficiency as light sources for short wavelengths. High carrier mobilities and breakdown electric fields were demonstrated for III-group nitrides, making them attractive for high frequency and high power applications. Currently, In-rich InGaN alloys and AlGaN/GaN high electron mobility structures are of high interest for the research community due to open fundamental questions.

    Electrical characterization techniques, commonly used for the determination of free charge carrier properties, require good ohmic and Schottky contacts, which in certain cases can be difficult to achieve. Access to electrical properties of buried conductive channels in multilayered structures requires modification of samples and good knowledge of the electrical properties of all electrical contact within the structure. Moreover, the use of electrical contacts to electrically characterize two-dimensional electronic materials, such as graphene, can alter their intrinsic properties. Furthermore, the determination of effective mass parameters commonly employs cyclotron resonance and Shubnikov-de Haas oscillations measurements, which require long scattering times of free charge carriers, high magnetic fields and low temperatures.

    The optical Hall effect is an external magnetic field induced optical anisotropy in  conductive layers due to the motion of the free charge carriers under the influence of the Lorentz force, and is equivalent to the electrical Hall effect at optical frequencies. The optical Hall effect can be measured by generalized ellipsometry and provides a powerful method for the determination of free charge carrier properties in a non-destructive and contactless manner. In principle, a single optical Hall effect measurement can provide quantitative information about free charge carrier types, concentrations, mobilities and effective mass parameters at temperatures ranging from few kelvins to room temperature and above. Further, it was demonstrated that for transparent samples, a backside cavity can be employed to enhance the optical Hall effect.

    Measurement of the optical Hall effect by generalized ellipsometry is an indirect technique requiring subsequent data analysis. Parameterized optical models are fitted to match experimentally measured ellipsometric data by varying physically significant parameters. Analysis of the optical response of samples, containing free charge carriers, employing optical models based on the classical Drude model, which is augmented with an external magnetic field contribution, provide access to the free charge carrier properties.

    The main research results of the graduate studies presented in this licentiate thesis are summarized in the five scientific papers.

    Paper I. Description of the custom-built terahertz frequency-domain spectroscopic ellipsometer at Linköping University. The terahertz ellipsometer capabilities are demonstrated by an accurate determination of the isotropic and anisotropic refractive indices of silicon and m-plane sapphire, respectively. Further, terahertz optical Hall effect measurements of an AlGaN/GaN high electron mobility structures were employed to extract the two-dimensional electron gas sheet density, mobility and effective mass parameters. Last, in-situ optical Hall effect measurement on epitaxial graphene in a gas cell with controllable environment, were used to study the effects of environmental doping on the mobility and carrier concentration.

    Paper II. Presents terahertz cavity-enhanced optical Hall measurements of the monolayer and multilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed p-type doping for monolayer graphene with a carrier density in the low 1012 cm−2 range and a carrier mobility of 1550 cm2/V·s. For the multilayer epitaxial graphene, n-type doping with a carrier density in the low 1013 cm−2 range, a mobility of 470 cm2/V·s and an effective mass of (0.14 ± 0.03) m0 were extracted. The measurements demonstrate that cavity-enhanced optical Hall effect measurements can be applied to study electronic properties of two-dimensional materials.

    Paper III. Terahertz cavity-enhanced optical Hall effect measurements are employed to study anisotropic transport in as-grown monolayer, quasi free-standing monolayer and quasi free-standing bilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed a strong anisotropy in the carrier mobilities of the quasi freestanding bilayer graphene. The anisotropy is demonstrated to be induced by carriers scattering at the step edges of the SiC, by showing that the mobility is higher along the step than across them. The scattering mechanism is discussed based on the results of the optical Hall effect, low-energy electron microscopy, low-energy electron diffraction and Raman measurements.

    Paper IV. Mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect measurements are employed to determine the electron effective mass in an In0.33Ga0.67N epitaxial layer. The data analysis reveals slightly anisotropic effective mass and carrier mobility parameters together with the optical phonon frequencies and broadenings.

    Paper V. Terahertz cavity-enhanced optical Hall measurements are employed to study the free charge carrier properties in a set of AlGaN/GaN high electron mobility structures with modified interfaces. The results show that the interface structure has a significant effect on the free charge carrier mobility and that the sample with a sharp interface between an AlGaN barrier and a GaN buffer layers exhibits a record mobility of 2332±73 cm2/V·s. The determined effective mass parameters showed an increase compared to the GaN value, that is attributed the the penetration of the electron wavefunction into the AlGaN barrier layer.

    List of papers
    1. Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
    Open this publication in new window or tab >>Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
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    2017 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 421, p. 357-360Article in journal (Refereed) Published
    Abstract [en]

    Cavity-enhanced optical Hall effect at terahertz (THz) frequencies is employed to determine the free charge carrier properties in epitaxial graphene (EG) with different number of layers grown by high-temperature sublimation on 4H-SiC(0001). We find that one monolayer (ML) EG possesses p-type conductivity with a free hole concentration in the low 1012 cmᅵᅵᅵ2 range and a free hole mobility parameter as high as 1550 cm2/Vs. We also find that 6 ML EG shows n-type doping behavior with a much lower free electron mobility parameter of 470 cm2/Vs and an order of magnitude higher free electron density in the low 1013 cmᅵᅵᅵ2 range. The observed differences are discussed. The cavity-enhanced THz optical Hall effect is demonstrated to be an excellent tool for contactless access to the type of free charge carriers and their properties in two-dimensional materials such as EG.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    THz optical Hall effect, Epitaxial graphene, Free charge carrier properties
    National Category
    Physical Sciences Condensed Matter Physics Atom and Molecular Physics and Optics Ceramics
    Identifiers
    urn:nbn:se:liu:diva-132407 (URN)10.1016/j.apsusc.2016.10.023 (DOI)000408756700015 ()
    Note

    Funding agencies: Swedish Research Council (VR) [2013-5580]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486, 2014-04712]; Swedish foundation for strategic research (SSF) [FFL12-0181, RIF14-055]

    Available from: 2016-11-09 Created: 2016-11-09 Last updated: 2023-12-28Bibliographically approved
    2. Properties of two-dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity-enhanced THz optical Hall effect
    Open this publication in new window or tab >>Properties of two-dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity-enhanced THz optical Hall effect
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    2016 (English)In: Physica Status Solidi C-Current Topics in Solid State Physics, Vol 13 No 5-6, Wiley-VCH Verlagsgesellschaft, 2016, Vol. 13, no 5-6, p. 369-373Conference paper, Published paper (Refereed)
    Abstract [en]

    In this work we employ terahertz (THz) ellipsometry to determine two-dimensional electron gas (2DEG) density, mobility and effective mass in AlGaN/GaN high electron mobility transistor structures grown on 4H-SiC substrates. The effect of the GaN interface exposure to low-flow-rate trimethylaluminum (TMA) on the 2DEG properties is studied. The 2DEG effective mass and sheet density are determined tobe in the range of 0.30-0.32m0 and 4.3-5.5×1012 cm–2, respectively. The 2DEG effective mass parameters are found to be higher than the bulk effective mass of GaN, which is discussed in view of 2DEG confinement. It is shown that exposure to TMA flow improves the 2DEG mobility from 2000 cm2/Vs to values above 2200 cm2/Vs. A record mobility of 2332±61 cm2/Vs is determined for the sample with GaN interface exposed to TMA for 30 s. This improvement in mobility is suggested to be due to AlGaN/GaN interface sharpening causing the reduction of interface roughness scattering of electrons in the 2DEG.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2016
    Series
    Physica Status Solidi C-Current Topics in Solid State Physics, ISSN 1862-6351
    Keywords
    AlGaN/GaN HEMTs, THz ellipsometry, 2DEG properties, THz optical Hall effect
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-133135 (URN)10.1002/pssc.201510214 (DOI)000387957200045 ()
    Conference
    11th International Conference on Nitride Semiconductors (ICNS), Beijing, China, August 30-September 4. 2015
    Available from: 2016-12-12 Created: 2016-12-09 Last updated: 2023-12-28Bibliographically approved
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    Study of novel electronic materials by mid-infrared and terahertz optical Hall effect
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  • 9.
    Arvidsson, Emma
    et al.
    Linköping University, Department of Mechanical Engineering.
    Ekblad, Emma
    Linköping University, Department of Mechanical Engineering.
    Framtagning av krypmodell för termomekanisk FE-analys av grenrör2006Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [sv]

    Grenrören i en motor utsätts för stora termiska och mekaniska belastningar, vilka gör att grenrören ofta spricker. Idag kan inte sprickbildningen fullständigt uttydas ur beräkningarna, syftet med arbetet är därför att se om dessa kan förbättras genom att använda en mer avancerad krypmodell än den som används idag.

    Ett förslag till krypmodell har tagits genom att studera ett antal i litteraturen funna modeller. De som valts ut är modeller enligt Norton, Bailey-Norton, Marin-Pao, Picket och Findley. Parametrarna i de olika modellerna har bestämts genom kurvanpassning av enaxliga prov på de aktuella grenrörsmaterialen. Resultaten visar att modellerna enligt Marin-Pao, Picket och Findley alla kan beskriva mätkurvorna nästan exakt. Problem uppstår dock med att man får parametrar som beror av både spänning och temperatur. Av dessa tre modeller anses Marin-Pao vara den bästa, då det är den av de tre som har minst antal parametrar. Utvärderingen ger vidare att Norton är den modell som är enklast, och beaktat över alla prover, den vars resultat bäst ansluter sig till mätdata. Valet görs att gå vidare med både Marin-Paos och Nortons modell.

    De två aktuella modellerna har lagts in som subrutiner till FE-programmet ABAQUS. Tester av modellerna görs först på ett litet kubiskt element och sedan på hela grenröret. Jämförelser görs mellan Norton, Marin-Pao och den modell som används idag – ”Two-layer viscoplasticity model”. Såväl Marin-Paos modell som Nortons beskriver verkligheten bättre än den idag använda modellen och av de båda är Nortons modell den som mest tillfredställande speglar verkligheten. Det är dessutom den modell som är mest stabil och beräkningsmässigt effektivast. Som en rekommendation inför fortsatt arbete föreslås därför användning av Nortons modell, samt ett utökat antal krypprover.

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  • 10.
    Aziz, Shazed
    et al.
    Department of Chemical and Environmental Engineering, Faculty of Engineering, University Putra Malaysia, Selangor, Malaysia.
    Suraya, A. R.
    Department of Chemical and Environmental Engineering, Faculty of Engineering, University Putra Malaysia, Selangor, Malaysia; Nanotechnology and Nanomaterials Group, Materials Processing and Technology Laboratory, Institute of Advanced Technology, University Putra Malaysia, Selangor, Malaysia.
    Rahmanian, S.
    Nanotechnology and Nanomaterials Group, Materials Processing and Technology Laboratory, Institute of Advanced Technology, University Putra Malaysia, Selangor, Malaysia.
    Salleh, M.A. Mohd
    Department of Chemical and Environmental Engineering, Faculty of Engineering, University Putra Malaysia, Selangor, Malaysia; Nanotechnology and Nanomaterials Group, Materials Processing and Technology Laboratory, Institute of Advanced Technology, University Putra Malaysia, Selangor, Malaysia.
    Effect of fibre coating and geometry on the tensile properties of hybrid carbon nanotube coated carbon fibre reinforced composite2014In: Materials & Design, ISSN 0261-3069, Vol. 54, p. 660-669Article in journal (Refereed)
    Abstract [en]

    Hierarchically structured hybrid composites are ideal engineered materials to carry loads and stresses due to their high in-plane specific mechanical properties. Growing carbon nanotubes (CNTs) on the surface of high performance carbon fibres (CFs) provides a means to tailor the mechanical properties of the fibre–resin interface of a composite. The growth of CNT on CF was conducted via floating catalyst chemical vapor deposition (CVD). The mechanical properties of the resultant fibres, carbon nanotube (CNT) density and alignment morphology were shown to depend on the CNT growth temperature, growth time, carrier gas flow rate, catalyst amount, and atmospheric conditions within the CVD chamber. Carbon nanotube coated carbon fibre reinforced polypropylene (CNT-CF/PP) composites were fabricated and characterized. A combination of Halpin–Tsai equations, Voigt–Reuss model, rule of mixture and Krenchel approach were used in hierarchy to predict the mechanical properties of randomly oriented short fibre reinforced composite. A fractographic analysis was carried out in which the fibre orientation distribution has been analyzed on the composite fracture surfaces with Scanning Electron Microscope (SEM) and image processing software. Finally, the discrepancies between the predicted and experimental values are explained.

  • 11.
    Bai, Sai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Univ Oxford, England.
    Sakai, Nobuya
    Univ Oxford, England.
    Zhang, Wei
    Univ Oxford, England; Univ Lincoln, England.
    Wang, Zhiping
    Univ Oxford, England.
    Wang, Jacob T.-W.
    Univ Oxford, England.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Univ Oxford, England.
    Snaith, Henry J.
    Univ Oxford, England.
    Reproducible Planar Heterojunction Solar Cells Based on One-Step Solution-Processed Methylammonium Lead Halide Perovskites2017In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, no 1, p. 462-473Article in journal (Refereed)
    Abstract [en]

    Metal halide perovskites have been demonstrated as one of the most promising materials for low-cost and high-performance photovoltaic applications. However, due to the susceptible crystallization process of perovskite films on planar substrates and the high sensitivity of the physical and optoelectronic nature of the internal interfaces within the devices, researchers in different laboratories still experience poor reproducibility in fabricating efficient perovskite solar cells with planar heterojunction device structures. In this method paper, we present detailed information on the reagents, equipment, and procedures for the fabrication of planar perovskite solar cells in both "regular" n-i-p and "inverted" p-i-n architectures based on one-step solution-processed methylammonium lead triiodide (MAPbI(3)) perovskite films. We discuss key parameters affecting the crystallization of perovskite and the device interfaces. This method paper will provide a guideline for the reproducible fabrication of planar heterojunction solar cells based on MAPbI3 perovskite films. We believe that the shared experience on MA-based perovskite films and planar solar cells will be also useful for the optimization process of perovskites with varied compositions, and other emerging perovskite-based optoelectronic devices.

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  • 12.
    Balachandramurthi, Arun Ramanathan
    et al.
    Univ West, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Univ West, Sweden.
    Dixit, Nikhil
    Univ West, Sweden.
    Pederson, Robert
    Univ West, Sweden.
    Influence of defects and as-built surface roughness on fatigue properties of additively manufactured Alloy 7182018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 735, p. 463-474Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) and Selective Laser Melting (SLM) are powder bed based additive manufacturing (AM) processes. These, relatively new, processes offer advantages such as near net shaping, manufacturing complex geometries with a design space that was previously not accessible with conventional manufacturing processes, part consolidation to reduce number of assemblies, shorter time to market etc. The aerospace and gas turbine industries have shown interest in the EBM and the SLM processes to enable topology-optimized designs, parts with lattice structures and part consolidation. However, to realize such advantages, factors affecting the mechanical properties must be well understood - especially the fatigue properties. In the context of fatigue performance, apart from the effect of different phases in the material, the effect of defects in terms of both the amount and distribution and the effect of "rough" as-built surface must be studied in detail. Fatigue properties of Alloy 718, a Ni-Fe based superalloy widely used in the aerospace engines is investigated in this study. Four point bending fatigue tests have been performed at 20 Hz in room temperature at different stress ranges to compare the performance of the EBM and the SLM material to the wrought material. The experiment aims to assess the differences in fatigue properties between the two powder bed AM processes as well as assess the effect of two post-treatment methods namely - machining and hot isostatic pressing (HIP). Fractography and metallography have been performed to explain the observed properties. Both HIPing and machining improve the fatigue performance; however, a large scatter is observed for machined specimens. Fatigue properties of SLM material approach that of wrought material while in EBM material defects severely affect the fatigue life.

  • 13.
    Balachandramurthi, Arun Ramanathan
    et al.
    Univ West, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Univ West, Sweden.
    Hansson, Thomas
    Univ West, Sweden; GKN Aerosp Sweden AB, Sweden.
    Pederson, Robert
    Univ West, Sweden.
    Anisotropic fatigue properties of Alloy 718 manufactured by Electron Beam Powder Bed Fusion2020In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 141, article id 105898Article in journal (Refereed)
    Abstract [en]

    In this study, Alloy 718 specimens manufactured by Electron Beam Powder Bed Fusion process are subjected to two different post-treatments to have different microstructural features. Low cycle fatigue testing has been performed both parallel and transverse to the build direction. EB-PBF Alloy 718 exhibits anisotropic fatigue behaviour; the fatigue life is better along the parallel direction compared to the transverse direction. The anisotropy in fatigue life is related to the anisotropy in the Youngs modulus. The pseudo-elastic stress vs. fatigue life approach is presented as a potential solution to handle anisotropy in fatigue life assessment of additively manufactured engineering components.

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  • 14.
    Bergström, Alexander
    Linköping University, Department of Management and Engineering, Carl Malmsten - furniture studies. Linköping University, The Institute of Technology.
    Träkärnor i alpina skidor: ett examensarbete kring olika träslag och dess egenskaper som träkärna i alpina skidor.2014Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The purpose of this work is to produce the most optimal wood core with the desired requirements in an all-mountain ski using Scandinavian wood. The study is descriptive and quantitative as it aims to measure the rate of change under the influence of wood species. In order to collect data for my research questions, tests have been carried out which generate data collection. A preliminary investigation was done with interviews to obtain a more detailed basis for constructing the method I would use in the final work. The results of the study showed that the wood type beech had the best results in terms of flexural strength. Ash had the best results when it came to tests on torsional rigidity. The down side of these woods is that they are too heavy. The lightest wood species of those involved in the tests was poplar. Therefore, I have chosen to combine species in the final wood core. Two different suggestions have been developed. One with a combination of beech and poplar, the other one with ash and poplar. The first provides a relatively light ski with good flexural strength. The second produced a light ski with good torsional rigidity. These two wood cores will be used in the construction of my skis and tested on the mountain.

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  • 15.
    Bernard, Christophe
    et al.
    Aix Marseille Université, INS, Marseille, France; Inserm, UMR_S 1106, Marseille, France.
    Simon, Daniel
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Malliaras, George G
    Department of Bioelectronics, Ecole Nationale Supérieure des Mines, CMP-EMSE, MOC, Gardanne, France.
    Organic Bioelectronics for Interfacing with the Brain2016In: The WSPC Reference on Organic Electronics: Organic Semiconductors: Volume 2: Fundamental Aspects of Materials and Applications / [ed] Seth R Marder, Jean-Luc Bredas, World Scientific, 2016, p. 345-368Chapter in book (Other academic)
    Abstract [en]

    Understanding how the brain works represents probably the most important fundamental endeavor of humankind and holds the key for the development of new technologies that can help improve the lives of people suffering from neurological conditions such as epilepsy and Parkinson's disease. Over the past decade, the use of organic electronic devices to interface with the biological world has received a great deal of attention and bloomed into a field now called “organic bioelectronics”. One of the key differences of organic from traditional electronic materials is their capacity to exchange ions with electrolytes. We discuss how this property can be leveraged to design new types of devices that interface with the brain.Read 

  • 16.
    Blomstedt, Mats
    et al.
    Siemens Industrial Turbomachinery AB, Finspång.
    Lindgren, Håkan
    Siemens Industrial Turbomachinery AB, Finspång.
    Olausson, Hans-Lennart
    Siemens Industrial Turbomachinery AB, Finspång.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Innovative starting procedure of Siemens SGT-600 in cold climate conditions2011In: ASME 2011 Turbo Expo:Turbine Technical Conference and Exposition: Volume 4: Cycle Innovations; Fans and Blowers; Industrial and Cogeneration; Manufacturing Materials and Metallurgy; Marine; Oil and Gas Applications, The American Society of Mechanical Engineers (ASME) , 2011, Vol. 4, p. 1021-1026Conference paper (Refereed)
    Abstract [en]

    A start-up of a gas turbine means that stress and forces are put on the machine. A start-up in cold climate conditions means that the forces are more critical since the material in the machine becomes more brittle. At a certain temperature the material is utilized to its limits (with appropriate margins applied) and for the SGT-600 ambient temperatures below -30°C (-22°F) become critical. In earlier installations in an arctic climate, an electric pre- heater has been utilized to prevent the critical components from becoming too brittle. This additional hardware costs money, is consuming auxiliary power and may contribute to unavailability. Another way to solve this issue may be to install material that is less brittle, but this will also increase the cost of the installation. Siemens is now applying an improved control logic during start-up, solving this issue in the software, without any additional hardware and avoiding unnecessary material changes. This new innovative start-up procedure is performing an automatic check of the stress levels before loading the machine, resulting in a safe and reliable start at temperatures below -30°C (-22°F). 

  • 17. Order onlineBuy this publication >>
    Bouhafs, Chamseddine
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Structural and Electronic Properties of Graphene on 4H- and 3C-SiC2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Graphene is a one-atom-tick carbon layer arranged in a honeycomb lattice. Graphene was first experimentally demonstrated by Andre Geim and Konstantin Novoselov in 2004 using mechanical exfoliation of highly oriented pyrolytic graphite (exfoliated graphene flakes), for which they received the Nobel Prize in Physics in 2010. Exfoliated graphene flakes show outstanding electronic properties, e.g., very high free charge carrier mobility parameters and ballistic transport at room temperature. This makes graphene a suitable material for next generation radio-frequency and terahertz electronic devices. Such applications require fabrication methods of large-area graphene compatible with electronic industry. Graphene grown by sublimation on silicon carbide (SiC) offers a viable route towards production of large-area, electronic-grade material on semi-insulating substrate without the need of transfer. Despite the intense investigations in the field, uniform wafer-scale graphene with very high-quality that matches the properties of exfoliated graphene has not been achieved yet. The key point is to identify and control how the substrate affects graphene uniformity, thickness, layer stacking, structural and electronic properties. Of particular interest is to understand the effects of SiC surface polarity and polytype on graphene properties in order to achieve large-area material with tailored properties for electronic applications. The main objectives of this thesis are to address these issues by investigating the structural and electronic properties of epitaxial graphene grown on 4HSiC and 3C-SiC substrates with different surface polarities. The first part of the thesis includes a general description of the properties of graphene, bilayer graphene and graphite. Then, the properties of epitaxial graphene on SiC by sublimation are detailed. The experimental techniques used to characterize graphene are described. A summary of all papers and contribution to the field is presented at the end of Part I. Part II consists of seven papers.

    List of papers
    1. Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)
    Open this publication in new window or tab >>Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)
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    2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, p. 085701-Article in journal (Refereed) Published
    Abstract [en]

    Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn. (C) 2015 AIP Publishing LLC.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2015
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-117253 (URN)10.1063/1.4908216 (DOI)000351132500070 ()
    Note

    Funding Agencies|Marie Curie actions [264613-NetFISiC]; Swedish Research Council (VR) [2011-4447, 2013-5580]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486]; Swedish foundation for strategic research (SSF) [FFL12-0181]; FP7 EU project Nano-Rf [FP7-ICT-2011-8]; French ANR under the Grafonics Project [ANR-10-NANO-0004]; European Union Seventh Framework Programme under Graphene Flagship [604391]; Knut and Alice Wallenbergs foundation

    Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2023-12-28
    2. Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
    Open this publication in new window or tab >>Cavity-enhanced optical Hall effect in epitaxial graphene detected at terahertz frequencies
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    2017 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 421, p. 357-360Article in journal (Refereed) Published
    Abstract [en]

    Cavity-enhanced optical Hall effect at terahertz (THz) frequencies is employed to determine the free charge carrier properties in epitaxial graphene (EG) with different number of layers grown by high-temperature sublimation on 4H-SiC(0001). We find that one monolayer (ML) EG possesses p-type conductivity with a free hole concentration in the low 1012 cmᅵᅵᅵ2 range and a free hole mobility parameter as high as 1550 cm2/Vs. We also find that 6 ML EG shows n-type doping behavior with a much lower free electron mobility parameter of 470 cm2/Vs and an order of magnitude higher free electron density in the low 1013 cmᅵᅵᅵ2 range. The observed differences are discussed. The cavity-enhanced THz optical Hall effect is demonstrated to be an excellent tool for contactless access to the type of free charge carriers and their properties in two-dimensional materials such as EG.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    THz optical Hall effect, Epitaxial graphene, Free charge carrier properties
    National Category
    Physical Sciences Condensed Matter Physics Atom and Molecular Physics and Optics Ceramics
    Identifiers
    urn:nbn:se:liu:diva-132407 (URN)10.1016/j.apsusc.2016.10.023 (DOI)000408756700015 ()
    Note

    Funding agencies: Swedish Research Council (VR) [2013-5580]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486, 2014-04712]; Swedish foundation for strategic research (SSF) [FFL12-0181, RIF14-055]

    Available from: 2016-11-09 Created: 2016-11-09 Last updated: 2023-12-28Bibliographically approved
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    Structural and Electronic Properties of Graphene on 4H- and 3C-SiC
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  • 18.
    Broitman, Esteban
    et al.
    University of Buenos Aires, Argentina.
    Latorre, Daniel
    University of Buenos Aires, Argentina.
    Sendra, Claudia
    University of Buenos Aires.
    Zimmerman, Rosa
    University of Buenos Aires.
    Thin Film Humidity Sensors (Sensores de Humedad de Película Delgada)1991In: Anales AFA, ISSN 1850-1158, Vol. 2, no 1, p. 277-279Article in journal (Refereed)
    Abstract [en]

    In this paper the construction and characterization of a humidity sensor with an alumina thin film responsive element is described. The capacitive sensor, made by thin film technology, consists of a dielectric layer of Al2O3 film deposited between metal electrodes.

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  • 19.
    Burström, Johanna
    Linköping University, Department of Management and Engineering, Malmstens Linköping University.
    Handarbetade inslag i moderna sammanhang: ett utforskande arbete om bildhuggeri ur en möbelsnickares perspektiv2020Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This is an exploratory work where I would like to draw attention to a craft that is quite unknown by people in general today. As a cabinetmaker I have examined a related craft, woodcarving, with the purpose to learn more about the technique and spread knowledge about the possibilities of the craft. One question I would like to lift is how woodcarving can be applied in modern furniture and products. My approach is that hand carved decorative elements can add value to a product, and that this ought to be possible to practice in a small-scale production. In my work interviews with active woodcarvers, practical tests and literature lead to a process to create a form. The work resulted in a collection of products with wood carved decorative elements, which in a variety of degree are suitable for a small-scale production.

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  • 20.
    Calamba, Katherine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Univ Lorraine, France; Sandvik Coromant AB, Sweden.
    Salamania, Janella
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Johnson, L. J. S.
    Sandvik Coromant AB, Sweden.
    Boyd, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Pierson, J. F.
    Univ Lorraine, France.
    Sortica, M. A.
    Uppsala Univ, Sweden.
    Primetzhofer, D.
    Uppsala Univ, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Effect of nitrogen vacancies on the growth, dislocation structure, and decomposition of single crystal epitaxial (Ti1-xAlx)N-y thin films2021In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 203, article id 116509Article in journal (Refereed)
    Abstract [en]

    The effect of varying nitrogen vacancies on the growth, microstructure, spinodal decomposition and hardness values of predominantly single crystal cubic phase c-(Ti1-xAlx)N-y films was investigated. Epitaxial c-(Ti1-xAlx)N-y films with y = 0.67, 0.79, and 0.92 were grown on MgO(001) and MgO(111) substrates by magnetron sputter deposition. High N vacancy c-(Ti1-xAlx)N-0.67 films deposited on MgO(111) contained coherently oriented w-(0001) structures while segregated conical structures were observed on the films grown on MgO(001). High resolution STEM images revealed that the N-deficient growth conditions induced segregation with small compositional fluctuations that increase with the number of N vacancies. Similarly, strain map analysis of the epitaxial c-(Ti1-xAlx)N-y (001) and (111) films show fluctuations in strain concentration that scales with the number of N vacancies and increases during annealing. The spinodal decomposition coarsening rate of the epitaxial c-(Ti1-xAlx)N-y films was observed to increase with decreasing N vacancies. Nanoindentation showed decreasing trends in hardness of the as-deposited films as the N vacancies increase. Isothermal post-anneal at 1100 degrees C in vacuum for 120 min revealed a continuation in the increase in hardness for the film with the largest number of N vacancies (y = 0.67) while the hardness decreased for the films with y = 0.79 and 0.92. These results suggest that nitrogen-deficient depositions of c-(Ti1-xAlx)N-y films help to promote a self-organized phase segregation, while higher N vacancies generally increase the coherency strain which delays the coarsening process and can influence the hardness at high temperatures. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd.

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  • 21.
    Calamba, Katherine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Lorraine, France.
    Schramm, Isabella
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Saarland University, Germany.
    Johansson Jöesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Ghanbaja, J.
    University of Lorraine, France.
    Pierson, J. F.
    University of Lorraine, France.
    Mucklich, F.
    Saarland University, Germany.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 122, no 6, article id 065301Article in journal (Refereed)
    Abstract [en]

    Aspects on the phase stability and mechanical properties of nitrogen deficient (Ti0.54Al0.46)N-y alloys were investigated. Solid solution alloys of (Ti,Al)N were grown by cathodic arc deposition. The kinetic energy of the impinging ions was altered by varying the substrate bias voltage from -30V to -80 V. Films deposited with a high bias value of -80V showed larger lattice parameter, finer columnar structure, and higher compressive residual stress resulting in higher hardness than films biased at -30V when comparing their as-deposited states. At elevated temperatures, the presence of nitrogen vacancies and point defects (anti-sites and self-interstitials generated by the ion-bombardment during coating deposition) in (Ti0.54Al0.46)N-0.87 influence the driving force for phase separation. Highly biased nitrogen deficient films have point defects with higher stability during annealing, which cause a delay of the release of the stored lattice strain energy and then accelerates the decomposition tendencies to thermodynamically stable c-TiN and w-AlN. Low biased nitrogen deficient films have retarded phase transformation to w-AlN, which results in the prolongment of age hardening effect up to 1100 degrees C, i.e., the highest reported temperature for Ti-Al-N material system. Our study points out the role of vacancies and point defects in engineering thin films with enhanced thermal stability and mechanical properties for high temperature hard coating applications. Published by AIP Publishing.

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  • 22.
    Carlsson, Karin
    Linköping University, Department of Management and Engineering.
    A Study of Failure Development in Thick Thermal Barrier Coatings2007Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [en]

    Thermal barrier coatings (TBC) are used for reduction of component temperatures in gas turbines. The service temperature for turbines can be as high as 1100ºC and the components are exposed to thermal cycling and gases that will cause the component to oxidize and corrode. The coatings are designed to protect the substrate material from this, but eventually it will lead to failure of the TBC. It is important to have knowledge about when this failure is expected, since it is detrimental for the gas turbine.

    The scope of this thesis has been to see if an existing life model for thin TBC also is valid for thick TBC. In order to do so, a thermal cycling fatigue test, a tensile test and finite element calculation have been performed. The thermal cycling fatigue test and finite element calculation were done to find correlations between the damage due to thermal cycling, the number of thermal cycles and the energy release rate. The tensile test was preformed to find the amount accumulated strain until damage.

    The thermal cycling lead to failure of the TBC at the bond coat/top coat interface. The measurment of damage, porosity and thickness of thermally grown oxide were unsatisfying due to problems with the specimen preparation. However, a tendency for the damage development were seen. The finite element calculations gave values for the energy release rate the stress intensity factors in mode~I and mode~II that can be used in the life model. The tensile test showed that the failure mechanism is dependent of the coating thickness and it gave a rough value of the maximum strain acceptable.

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  • 23.
    Chai, G.
    et al.
    R and D Centre, Sandvik Materials Technology, Sandviken, Sweden.
    Lillbacka, R.
    FS Dynamics, Göteborg, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Micro heterogeneous deformation and strain localization behavior in austenitic ferritic duplex stainless steels2011In: Advances in heterogeneous material mechanics 2011: proceedings of the Third International Conference on Heterogeneous Material Mechanics, Destech Publications , 2011, p. 186-193Conference paper (Other academic)
    Abstract [en]

    This paper provides a review on the recent work done on the micro heterogeneous deformation and strain localization behavior in austenitic ferritic duplex stainless steels studied using TEM, SEM and in-situ X-ray diffractometer and neutron diffractometer and the simulation using multi-scale material modelling. The results from both studies show that the difference in the elasto-plastic properties of the austenite and ferrite phases has caused different amounts of plastic deformations occurring in these two phases, and consequently different static and cyclic stress strain behaviours and substructures. From the simulations it is found that the coupling effect plays a key role in producing the changes in the cyclic stress-strain behaviour and also on the substructure evolution. TEM investigation also shows that the dislocation slipping behaviour and substructures strongly depend on the elasto-plastic properties of the individual phases and also on the coupling effect. The study indicates that the material damage and crack initiation in a two phase metal start mainly in the weakest phase if the deformation hardening is considered.

  • 24.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Alleima, Sweden.
    Bergstrom, Jens
    Karlstad Univ, Sweden.
    Burman, Christer
    Karlstad Univ, Sweden.
    Crack Initiation in Bulk Matrix of Austenitic Stainless Steel during Very High Cycle Fatigue2023In: Materials Performance and Characterization, ISSN 2379-1365, E-ISSN 2165-3992Article in journal (Refereed)
    Abstract [en]

    In the very high cycle fatigue regime, fatigue crack initiation in high-strength steels is usually correlated to a subsurface inclusion with a fine granular area (FGA). Localized stress-strain concentration at the subsurface inclusion is a critical factor. Fatigue crack initiation with an FGA in the bulk matrix without any defect has rarely been reported. In this paper, a fundamental study on the formation of FGAs in the bulk matrix of an austenitic stainless steel has been carried out using a progressive stepwise load-increasing test with a cycle step of about 108 cycles. FGA formation in the subsurface bulk matrix has been observed. The micro structural damage in the fatigue-tested specimens has been studied using the electron channeling contrast imaging electron microscopy technique. Strain localization and grain fragmentation are the main processes for the formation of FGAs. Local plasticity exhaustion leads to crack initiation due to local stress concentrations. This method can also be used to predict the fatigue damage process, especially the damage rate in individual specimens.

  • 25.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Mat Technol, Sweden.
    Bergstrom, Jens
    Karlstad Univ, Sweden.
    Burman, Christer
    Karlstad Univ, Sweden.
    Formation of fine granular area in a non-defect matrix of austenitic stainless steel during very high cycle fatigue2023In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 46, no 6, p. 2364-2373Article in journal (Refereed)
    Abstract [en]

    A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

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  • 26.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. R&D Center, Sandvik Materials Technology, Sandviken, Sweden.
    Forsman, Tomas
    R&D Center, Sandvik Materials Technology, Sandviken, Sweden.
    Gustavsson, Fredrik
    R&D Center, Sandvik Materials Technology, Sandviken, Sweden.
    Microscopic and Nanoscopic Study on Subsurface Damage and Fatigue Crack Initiation During Very High Cycle Fatigue2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 83, no 2, p. 288-292Article in journal (Refereed)
    Abstract [en]

    “Fish eye” is a typical phenomenon of fatigue crack initiation at a subsurface defect such as inclusion during very high cycle fatigue. The formation of a fine grained area and micro-debonding is believed to cause fatigue crack initiation. This paper provides a basic study on the formation of the fine grained area in a martensitic stainless steel during very high cycle fatigue using scanning electron microscopy, SEM, focused ion beam technique, FIB, electron backscatter diffraction, EBSD, and electron channeling contrast imaging, ECCI. The results show that the formation of a fine grained zone is a local behavior. The fine grained zone is very near the fatigue crack initiation origin. In the transversal direction (cross section), the depth of the fine grained zone is only few micrometers. In the longitudinal direction (crack propagation direction), the depth of the fine grain zone is about one micrometer. ECCI analysis shows that in the fine grained area with high retained strain, high plastic deformation can be found. Dislocation slip bands can be observed. They interact with grain boundaries and cause the formation of damage due to impingement cracking. The results indicate that occurrence of plastic deformation in metallic material during very high cycle fatigue is very localized, mainly near the front of the crack tip or a defect.

  • 27.
    Chai, Guocai
    et al.
    Sandvik Materials Technology, Sandviken.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Slamecka, Karel
    Brno University of Technology, Czech Republic.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    In Situ SEM(EBSD analysis of fatigue crack propagation behavior of a super duplex stainless steel2008Conference paper (Refereed)
  • 28.
    Chason, E.
    et al.
    Brown University, USA.
    Karlson, M.
    Brown University, USA.
    Colin, J. J.
    University of Poitiers, France.
    Magnfält, Daniel
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Sarakinos, Kostas
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
    Abadias, G.
    University of Poitiers, France.
    A kinetic model for stress generation in thin films grown from energetic vapor fluxes2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 14, article id 145307Article in journal (Refereed)
    Abstract [en]

    We have developed a kinetic model for residual stress generation in thin films grown from energetic vapor fluxes, encountered, e.g., during sputter deposition. The new analytical model considers sub-surface point defects created by atomic peening, along with processes treated in already existing stress models for non-energetic deposition, i.e., thermally activated diffusion processes at the surface and the grain boundary. According to the new model, ballistically induced subsurface defects can get incorporated as excess atoms at the grain boundary, remain trapped in the bulk, or annihilate at the free surface, resulting in a complex dependence of the steady-state stress on the grain size, the growth rate, as well as the energetics of the incoming particle flux. We compare calculations from the model with in situ stress measurements performed on a series of Mo films sputter-deposited at different conditions and having different grain sizes. The model is able to reproduce the observed increase of compressive stress with increasing growth rate, behavior that is the opposite of what is typically seen under non-energetic growth conditions. On a grander scale, this study is a step towards obtaining a comprehensive understanding of stress generation and evolution in vapor deposited polycrystalline thin films. Published by AIP Publishing.

  • 29.
    Chen, Ding-Yuan
    et al.
    SweGaN AB, Linkoping, Sweden; Chalmers Univ Technol, Sweden.
    Persson, Axel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. TheMAC, Sweden; Lund Univ, Sweden; Lund Univ, Sweden.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Chen, Jr-Tai
    SweGaN AB, Linkoping, Sweden.
    Rorsman, Niklas
    Chalmers Univ Technol, Sweden.
    Structural investigation of ultra-low resistance deeply recessed sidewall ohmic contacts for AlGaN/GaN HEMTs based on Ti/Al/Ti-metallization2023In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 38, no 10, article id 105006Article in journal (Refereed)
    Abstract [en]

    This study presents a novel approach to forming low-resistance ohmic contacts for AlGaN/GaN HEMTs. The optimized contacts exhibit an outstanding contact resistance of approximately 0.15 & omega;& BULL;mm. This is achieved by firstly recessing the barrier of the heterostructure to a depth beyond the channel. In this way, the channel region is exposed on the sidewall of the recess. The coverage of the Ti/Al/Ti ohmic metalization on the sidewall is ensured through tilting of the sample during evaporation. The annealing process is performed at a low temperature of 550 & DEG;C. The approach does not require precise control of the recess etching. Furthermore, the method is directly applicable to most barrier designs in terms of thickness and Al-concentration. The impact of recessed sidewall angle, thickness and ratio of Ti and Al layers, and the annealing procedure are investigated. Structural and chemical analyses of the interface between the ohmic contacts and epi-structure indicate the formation of ohmic contacts by the extraction of nitrogen from the epi-structure. The approach is demonstrated on HEMT-structures with two different barrier designs in terms of Al-concentration and barrier thickness. The study demonstrate large process window in regard to recess depth and duration of the annealing as well as high uniformity of the contact resistance across the samples, rendering the approach highly suitable for industrial production processes.

  • 30.
    Chen, Hsin-Yu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Selective Area Growth of AlGaN pyramid with GaN Multiple Quantum Wells2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

      Since Shuji Nakamura, Hiroshi Amano, and Isamu Akasaki won the 2014 Nobel prize in Physics owing to theircontributions on the invention of efficient blue GaN light emitting diodes, GaN became an even more appealingmaterial system in the research field of optoelectronics. On the other hand, quantum structures or low-dimensionalstructures with properties derived from quantum physics demonstrate superior and unique electrical and opticalproperties, providing a significant potential on novel optoelectronic applications based on the employment of quantumconfinement.

      In 2012, our research team at Linköping University utilized pyramid templates, which is an established approach toform quantum structures, to successfully grow GaN pyramids with InGaN hybrid quantum structures, includingquantum wells, quantum wires, and quantum dots. This growth enabled site-controlled pyramids based on selectivearea growth (SAG). After numerous studies on the photoluminescence properties, the mature and controlled growthtechnique was proposed to be adapted for fabrication of AlGaN pyramids on which GaN hybrid quantum structurescan be hosted.

      This thesis is dedicated to the subsequent problems of the growth of AlGaN pyramids. It was found that there wasan undesired deposition of a considerable thickness on top the desired AlGaN pyramid with GaN multiple quantumwells. In this thesis, two different directions are explored to find the key solution with a potential of furtheroptimization. On one hand, the growth parameters such as precursors cut-off, carrier gas during cooling, temperatureholding, cooling pressure, III/V ratio, and the possible effect of GaN surfaces are investigated. However, due to theactual inherent properties of the metal-organic chemical vapor deposition reactor used, no promising parameter tuningcan been identified. On the other hand, from post-growth point of view, a KOH aqueous etching solution exhibits apositive result toward removing the undesired deposition. This etching process is suggested to be further optimized toachieve the final goal of eliminating the undesired deposition.

    Download full text (pdf)
    2018 MSc Thesis_H.Y. Chen_Selective Area Growth of AlGaN pyramid with GaN Multiple Quantum Wells
  • 31. Order onlineBuy this publication >>
    Chen, Zhe
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Surface Integrity and Fatigue Performance of Nickel-based Superalloys2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

    List of papers
    1. Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures
    Open this publication in new window or tab >>Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures
    Show others...
    2016 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47A, no 7, p. 3664-3676Article in journal (Refereed) 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.

    Place, publisher, year, edition, pages
    Springer, 2016
    Keywords
    Structural integrity, Broaching, Inconel 718, Plastic deformation, Residual stresses, Thermal exposure, Superalloy
    National Category
    Materials Engineering Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-111056 (URN)10.1007/s11661-016-3515-6 (DOI)000377434700041 ()
    Funder
    Linköpings universitet, 2009-00971
    Note

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

    Available from: 2014-10-06 Created: 2014-10-06 Last updated: 2018-02-27Bibliographically approved
    2. On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 718
    Open this publication in new window or tab >>On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 718
    Show others...
    2016 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 671, p. 158-169Article in journal (Refereed) 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.

    Keywords
    Broaching, Inconel 718, Surface integrity, thermal impact, Fatigue, Crack initiation
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-129843 (URN)10.1016/j.msea.2016.06.030 (DOI)000381165400016 ()
    Note

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

    Available from: 2016-06-29 Created: 2016-06-29 Last updated: 2017-11-28
    3. Nano-scale characterization of white layer in broached Inconel 718
    Open this publication in new window or tab >>Nano-scale characterization of white layer in broached Inconel 718
    Show others...
    2017 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 684, p. 373-384Article in journal (Refereed) 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.

    Place, publisher, year, edition, pages
    Amsterdam: Elsevier, 2017
    Keywords
    Surface integrity; White layer; Broaching; Inconel 718; Adiabatic shear band; Mechanically-based subgrain rotation
    National Category
    Materials Chemistry Inorganic Chemistry Other Materials Engineering Paper, Pulp and Fiber Technology Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-134123 (URN)10.1016/j.msea.2016.12.045 (DOI)000393938300045 ()
    Note

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

    Available from: 2017-01-24 Created: 2017-01-24 Last updated: 2017-11-29Bibliographically approved
    4. Surface Integrity and Fatigue Performance of Inconel 718 in Wire Electrical Discharge Machining
    Open this publication in new window or tab >>Surface Integrity and Fatigue Performance of Inconel 718 in Wire Electrical Discharge Machining
    2016 (English)In: 3RD CIRP CONFERENCE ON SURFACE INTEGRITY, 2016, Vol. 45, p. 307-310Conference paper, Published paper (Refereed)
    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.

    Series
    Procedia CIRP, ISSN 2212-8271
    Keywords
    wire electrical discharge machining (wire EDM), surface integrity, fatigue, crack initiation, Inconel 718
    National Category
    Materials Engineering Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-130582 (URN)10.1016/j.procir.2016.02.053 (DOI)000417326500077 ()
    Conference
    3rd CIRP Conference on Surface Integrity (CIRP CSI)8-10 June, 2016, Charlotte, USA
    Note

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

    Available from: 2016-08-17 Created: 2016-08-17 Last updated: 2022-09-28
    5. Effect of Cooling and Shot Peening on Residual Stresses and Fatigue Performance of Milled Inconel 718
    Open this publication in new window or tab >>Effect of Cooling and Shot Peening on Residual Stresses and Fatigue Performance of Milled Inconel 718
    Show others...
    2017 (English)In: Residual Stresses 2016 ICRS 10 / [ed] T.M. Holden, O. Muránsky, and L. Edwards, 2017, Vol. 2, p. 13-18Conference paper, Published paper (Refereed)
    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.

    Series
    Materials Research Proceedings, ISSN 2474-395X
    Keywords
    Residual stresses, surface integrity, milling, shot peening, superalloys, fatigue
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-132001 (URN)10.21741/9781945291173-3 (DOI)000401041500003 ()978-1-9452-9116-6 (ISBN)
    Conference
    10th International Conference on Residual Stresses ICRS-10, Sydney, Australia, 3-8 July 2016
    Note

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

    Available from: 2016-10-13 Created: 2016-10-13 Last updated: 2017-06-13Bibliographically approved
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  • 32.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Sundell, Gustav
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund University, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Nano-scale characterization of white layer in broached Inconel 7182017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 684, p. 373-384Article in journal (Refereed)
    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.

  • 33.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Surface Integrity and Fatigue Performance of Inconel 718 in Wire Electrical Discharge Machining2016In: 3RD CIRP CONFERENCE ON SURFACE INTEGRITY, 2016, Vol. 45, p. 307-310Conference paper (Refereed)
    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.

    Download full text (pdf)
    fulltext
  • 34.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, SE-61283 Finspång, Sweden.
    On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 7182016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 671, p. 158-169Article in journal (Refereed)
    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.

  • 35.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Avdovic, Pajazit
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund university.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures2016In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47A, no 7, p. 3664-3676Article in journal (Refereed)
    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.

    Download full text (pdf)
    fulltext
  • 36.
    Cong, D Y
    et al.
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Wang, Yandong
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Zetterström, P
    The Studsvik Neutron Research Laboratory, Uppsala University.
    Zhao, X
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Liaw, P K
    Dept of Materials Science and Eng, The University of Tennessee, Knoxville, USA.
    Zuo, L
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Crystal structures and textures in the hot-forged Ni-Mn-Ga shape memory alloys2006In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 37A, no 5, p. 1397-1403Article in journal (Refereed)
    Abstract [en]

    Three ferromagnetic shape-memory alloys with the chemical compositions of Ni53Mn25Ga22, Ni48Mn30Ga22, and Ni48Mn25Ga22Co5 were prepared by the induction-melting and hot-forging process. The crystal structures were investigated by the neutron powder diffraction technique, showing that Ni53Mn25Ga22 and Ni48Mn25Ga22Co5 have a tetragonal, I4/mmm martensitic structure at room temperature, while Ni48Mn30Ga22 has a cubic, L2(1) austenitic structure at room temperature. The development of textures in the hot-forged samples shows the in-plane plastic flow anisotropy from the measured pole figures by means of the neutron diffraction technique. Significant texture changes were observed for the Ni48Mn25Ga22Co5 alloy after room temperature deformation, which is due to the deformation-induced rearrangements of martensitic variants. An excellent shape-memory effect (SME) with a recovery ratio of 74 pct was reported in this Ni48Mn25Ga22Co5 polycrystalline alloy after annealing above the martensitic transformation temperature, and the "shape-memory" influence also occurs in the distributions of grain orientations.

  • 37.
    Cong, D Y
    et al.
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Wang, Yandong
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Zetterström, P
    The Studsvik Neutron Research Laboratory, Uppsala University.
    Zhao, X
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Liaw, P K
    Dept of Materials Science and Eng, The University of Tennessee, Knoxville, USA.
    Zuo, L
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Crystal Structures and Textures in the Hot-Froged Ni-Mn-Ga Shape Memory Alloys2006In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 37A, no 5, p. 1397-1403Article in journal (Refereed)
  • 38.
    Darabi, Sozan
    et al.
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Yang, Chiyuan
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. n Ink AB, Sweden.
    Li, Zerui
    Chalmers Univ Technol, Sweden; Sichuan Univ, Peoples R China.
    Huang, Jun-Da
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Hummel, Michael
    Aalto Univ, Finland.
    Sixta, Herbert
    Aalto Univ, Finland.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. n Ink AB, Sweden.
    Mueller, Christian
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Polymer-Based n-Type Yarn for Organic Thermoelectric Textiles2023In: Advanced Electronic Materials, E-ISSN 2199-160X, article id 2201235Article in journal (Refereed)
    Abstract [en]

    A conjugated-polymer-based n-type yarn for thermoelectric textiles is presented. Thermoelectric textile devices are intriguing power sources for wearable electronic devices. The use of yarns comprising conjugated polymers is desirable because of their potentially superior mechanical properties compared to other thermoelectric materials. While several examples of p-type conducting yarns exist, there is a lack of polymer-based n-type yarns. Here, a regenerated cellulose yarn is spray-coated with an n-type conducting-polymer-based ink composed of poly(benzimidazobenzophenanthroline) (BBL) and poly(ethyleneimine) (PEI). The n-type yarns display a bulk electrical conductivity of 8 x 10(-3) S cm(-1) and Seebeck coefficient of -79 mu V K-1. A promising level of air-stability for at least 13 days can be achieved by applying an additional thermoplastic elastomer coating. A prototype in-plane thermoelectric textile, produced with the developed n-type yarns and p-type yarns, composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated regenerated cellulose, displays a stable device performance in air for at least 4 days with an open-circuit voltage per temperature difference of 1 mV degrees C-1. Evidently, polymer-based n-type yarns are a viable component for the construction of thermoelectric textile devices.

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  • 39.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Strain-related structural and vibrational properties of group-III nitride layers and superlattices2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This PhD thesis is focused on strain-related phenomena in group-III nitride layers and heterostructures. Key issues in material properties as phonon mode behavior, structure and lattice parameters of AlN, InN and GaN, as well as of AlN/GaN superlattices are addressed in order to give answers to some open questions. The research is motivated by the enormous technological application potential of the group-III nitride materials for optoelectronic devices and high temperature, and high power devices. Due to the lack of native substrates, the group-III nitrides are typically grown on foreign substrates resulting inbuilt-in strain in the films, as well as, in misorientation and defect formation. Substantial efforts have been concentrated on the research of strain-related fundamental properties of group-III nitrides. However, some of the strain-related structural and vibrational properties of these materials remain unclear and this gap has to be filled in order to fully explore the possibilities for applications.The thesis contributes to the knowledge of the strain-related phenomena ingroup-III nitrides by concentrating on the following: i) lattice parameters and strain relaxation in GaN, AlN, InN films with different thicknesses, as well as free-standing GaN quasi-substrates; ii) phonon mode behavior and deformation potentials of AlN and InN; iii) structural evolution in AlN and GaN; iv)phonon mode behavior and strain evolution in AlN/GaN superlattices. The layers studied were grown by a variety of growth techniques and nucleation schemes aiming at establishing of a comprehensive understanding of the material properties.

    The thesis is organized as follows: In the first part a general description of the basic properties of group-III nitrides is given with a special emphasis on the structural and vibrational properties. The vibrational properties of lowdimensional group-III nitrides are also reviewed. After that, basic concepts of strain phenomenon in group-III nitrides, as well as the strain effects on phonons and on structural properties are discussed. Finally, the experimental techniques used are introduced.

    The second part of the thesis consists of six papers providing informationon specific strain-related structural and vibrational properties of III-nitride layers and superlattices.

    The lattice parameters of GaN films grown by two different techniques on a-plane sapphire are the subject of Paper I. We have determined two different values of the in-plane lattice parameter of the GaN layers in contrast to only one in the case of films grown on c-plane sapphire. We suggest that the observed distortion of the hexagonal symmetry can be attributed to the presence of anisotropic in-plane strain in the films. A new approach to determination of lattice parameters has been proposed.

    Paper II deals with the lattice parameters of GaN quasi-substrates grown by hydride vapor phase epitaxy using two nucleation schemes. The lattice parameters of both, Ga- and N-polar faces of the quasi-substrates were determined and compared. The strain relaxation phenomena in such free-standing layers and the concept of strain-free lattice parameters are discussed.

    Papers III and IV are devoted to the deformation potentials of the E 1 (TO)mode in AlN, and the E1 (TO) and E2 modes in InN, where a combination of infraredellipsometry, infrared reflection, Raman scattering and x-ray diffractionstudies was used. The reported results in Paper III present the first experimentalvalues for the E1 (TO) deformation potentials of AlN and the results for the InN deformation potentials in Paper IV are the first ever reported.

    The strain evolution and its effect on the structural and vibrational properties of thin epitaxial AlN layers with different thicknesses have been studied in Paper V. A model of the strain evolution with film thickness and related defect structure is suggested and it is successfully used in the infrared ellipsometry data analysis.

    Paper VI is focused on the strain evolution in AlN/GaN superlattices withdifferent periods and its effect on their phonon properties. The presence of phonons originating from the superlattice constituents was revealed and their nature is discussed.

    List of papers
    1. Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
    Open this publication in new window or tab >>Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
    Show others...
    2003 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 5, p. 703-705Article in journal (Refereed) Published
    Abstract [en]

    The lattice parameters of GaN layers grown on a-plane sapphire were investigated. The hydride vapor phase epitaxy and metalorganic vapor phase epitaxy were used for the determination of parameters. The strain anisotropy was found to have different values in the films and obtained values of parameters were grouped around two values.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46727 (URN)10.1063/1.1542931 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2023-12-28
    2. Deformation potentials of the E-1(TO) mode in AlN
    Open this publication in new window or tab >>Deformation potentials of the E-1(TO) mode in AlN
    Show others...
    2002 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 13, p. 2302-2304Article in journal (Refereed) Published
    Abstract [en]

    The deformation potentials of the E-1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made. (C) 2002 American Institute of Physics.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47892 (URN)10.1063/1.1465105 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2023-12-28
  • 40.
    De la Cruz Rodrígues, Pedro
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue and Corrosion Fatigue Fracture of a Plasma Nitrided, Laser Hardened, and Galvanized B-Mn Steel1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fundamental and technological aspects of fatigue and fracture of conventional and advanced material are topics of primary importance to the development of materials science and engineering. Surface treatments have been established to improve the surface properties of material against surface phenomenon such as wear, corrosion, fatigue and corrosion fatigue. This thesis deals with the influence of two modem (plasma nitriding and laser hardening), and one conventional (hot dip galvanizing), surface treatments on the fatigue, corrosion fatigue (in seawater) and fracture of a B-Mn steel. The main approach adopted here focuses the attention on fatigue crack initiation mechanisms.

    Constant stress amplitude plane reversed bending fatigue tests (R = -1) at room temperature and at a frequency of 47 Hz in air and sea water were conducted using cylindrical untreated and surface treated quenched and tempered (Q&T) steel specimens made of a B-Mn SS2131(∼AISI 15B21H) steel with stress concentration factors of Kt =1.05 and 1.7.

    S-N curves show that surface treatments improved the fatigue limit by 53 % and 115 % (plasma nitriding), and 18% and 56 % (laser hardening) of smooth and notched Q&T specimens; whereas hot dip galvanizing slightly decrease the air fatigue limit of smooth (-9 %) and notched (-10 %) Q&T specimens. The small cracks formed in the coating during galvanizing could be the cause of this reduction. Compressive stresses and improved strength (hardness) introduced by plasma nitriding and laser hardening play the principal role for the improvement of fatigue strength, subsurface crack nucleation, fish-eye asymmetry, and reduction of stress intensity factors. Plasma nitrided (PN) and laser hardened (LH) materials behaves as composites. Laser process parameters have to be optimised in order to avoid the formation of a damaged area (characterised by a low hardness and low compressive residual stresses) around the overlap zone which promotes the formation of long narrow crack along the edge of the overlap zone causing premature failure.

    Sea water suppress the fatigue limit and reduces fatigue strength (especially at long lives) of smooth and notched Q&T, PN and LH specimens, but smooth and notched hot dip galvanized (HDG) specimens still exhibit a corrosion fatigue limit (at 2x107 cycles) with values a little lower than the corresponding air fatigue limits. Physical and electrochemical corrosion protection by hot dip galvanizing are the causes for the good corrosion fatigue properties obtained. Plasma nitriding improves the corrosion fatigue resistance of Q&T specimens; it is associated to the good corrosion resistance of ε and -phases, the enhancement of corrosion and fatigue by compressive residual stresses and the consumption of H+ ions during reduction of nitrogen. Mechanisms for nucleation of pits, and corrosion fatigue cracks have been proposed to explain corrosion fatigue strength reduction due to sea water. A derived equation predict well the corrosion fatigue strength of notched specimens from the observed air fatigue strength of smooth specimens.

  • 41. Order onlineBuy this publication >>
    Deng, Dunyong
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. 202100-3096.
    On the Microstructures and Anisotropic Mechanical Behaviours of Additively Manufactured IN7182019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Additive manufacturing (AM), also known as 3D printing, offers great design flexibility for manufacturing components with complex geometries, and has attracted significant interest in the aero and energy industries in the past decades. Among the commercial AM processes, selective laser melting (SLM) and electron beam melting (EBM) are the two most widely used ones for metallic materials. Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties, weldability and low cost. Due to its excellent weldability, IN718 has been intensively applied in the AM filed, to gain more understanding of the AM processes and fully realize AM’s potentials.

    The study objects in the present thesis include both EBM and SLM IN718. The solidification conditions in EBM and SLM are very different and are different to that of conventional cast, leading to unique microstructures mechanical properties. Therefore, this thesis aims to gain better understanding of the microstructures and anisotropic mechanical behaviours of both EBM and SLM IN718, by detailed characterizations and by comparisons with the forged counterpart.

    The as-built microstructure of EBM IN718 is spatially dependent: the periphery (contour) region has a mixture of equiaxed and columnar grains, while the bulk (hatch) region has columnar grains elongated along the building direction; the last solidified region close to the top sample surface shows segregation and Laves phases, otherwise the rest of the whole sample is well homogenized. Differently, the as-built microstructure of SLM IN718 is spatially homogeneous: the grains is rather equiaxed and with subgrain cell structures. These microstructures also respond differently to the standard heat treatment routines for the conventional counterparts.

    Anisotropic mechanical properties are evident in the room temperature tensile tests and high temperature dwell-fatigue tests. The anisotropic tensile properties of EBM IN718 at room temperature are more likely due to the directional alignment of porosities along the building direction rather than the strong crysiii tallographic texture of 100 _ building direction. While for SLM IN718, the anisotropy is more likely attributed to the different extents of ‘work-hardening’ or dislocations accumulated between the horizontally and vertically built specimens. The anisotropy mechanisms in dwell-fatigue crack propagations at 550 C for EBM and SLM IN718 are identical: higher effective stress intensity factor when intergranular cracking path is perpendicular to the loading direction, but lower effective stress intensity factor when intergranular cracking path is parallel to or slightly deviated from the loading direction.

    The 2160s dwell-fatigue cracking behaviours at 550 C are of significant interest for AM IN718, of which test condition is similar to that of real service for IN718 disk in turbine engine. Generally, after conventional or short-term heat treatments, EBM IN718 shows better dwell-fatigue cracking resistance than SLM IN718. The damage mechanism is different for EBM and SLM IN718: the intergranular cracking in EBM IN718 is due to environmentally assisted grain boundary attack, while creep damage is active for SLM IN718. The considerably ‘deformed’ microstructure, specifically the subgrain cell structures in SLM IN718 resulted from the manufacturing process, is believed to activate creep damage even at a low temperature of 550 C. And for SLM IN718, heat treatment routine must be carefully established to alter the ‘deformed’ microstructure for better time dependent cracking resistance at elevated temperature.

    List of papers
    1. Microstructure and Anisotropic Mechanical Properties of EBM Manufactued Inconel 718 and Effects of Post Heat Treatment
    Open this publication in new window or tab >>Microstructure and Anisotropic Mechanical Properties of EBM Manufactued Inconel 718 and Effects of Post Heat Treatment
    2017 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 693, p. 151-163Article in journal (Refereed) Published
    Abstract [en]

    Materials manufactured with electron beam melting (EBM) have different microstructures and properties to those manufactured using conventional manufacturing methods. A detailed study of the microstructures and mechanical properties of Inconel 718 manufactured with EBM was performed in both as-manufactured and heat-treated conditions. Different scanning strategies resulted in different microstructures: contour scanning led to heterogeneous grain morphologies and weak texture, while hatch scanning resulted in predominantly columnar grains and strong 〈001〉 building direction texture. Precipitates in the as-manufactured condition included γ′, γ″, δ  , TiN and NbC, among which considerable amounts of γ″ yielded relatively high hardness and strength. Strong texture, directionally aligned pores and columnar grains can lead to anisotropic mechanical properties when loaded in different directions. Heat treatments increased the strength and led to different δ precipitation behaviours depending on the solution temperatures, but did not remove the anisotropy. Ductility seemed to be not significantly affected by heat treatment, but instead by the NbC and defects inherited from manufacturing. The study thereby might provide the potential processing windows to tailor the microstructure and mechanical properties of EBM IN718.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    Electron beam melting; Nickel based superalloy; Microstructure; Anisotropy; Mechanical properties; Heat treatments
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-137289 (URN)10.1016/j.msea.2017.03.085 (DOI)000401384400018 ()2-s2.0-85016252903 (Scopus ID)
    Note

    Funding agencies: Sandvik Machining Solutions AB in Sandviken, Sweden; Faculty Grant SFO-MAT-LiU at Linkoping University [2009-00971]; Chinese Scholarship Council; Agora Materiae

    Available from: 2017-05-10 Created: 2017-05-10 Last updated: 2019-11-07Bibliographically approved
    2. On the formation of microstructural gradients in a nickel-base superalloy during electron beam melting
    Open this publication in new window or tab >>On the formation of microstructural gradients in a nickel-base superalloy during electron beam melting
    2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 160, p. 251-261Article in journal (Refereed) Published
    Abstract [en]

    Electron beam melting (EBM) is one of the most widely used additive manufacturing (AM) methods for metallic components and has demonstrated great potential to fabricate high-end components in the aerospace and energy industries. The thermal condition within a melt pool and the complicated thermal cycles during the EBM process are of interest but not yet well-understood, and will significantly affect the microstructural homogeneity of as-manufactured nickel-base superalloy components. To establish the thermal profile evolution during electron beam melting of nickel-base superalloys, Inconel 718 (IN718) is manufactured and characterized in the as-manufactured condition, on account of its representative segregation and precipitation behaviours. The microstructure gradient within a build, specifically the Laves phase volume fraction evolution, is rationalized with the solidification condition and the following in-situ annealing. Precipitations of carbide/nitride/carbonitride, delta and gamma/gamma are also discussed. Hardness is measured and correlated to the Laves phase volume fraction evolution and the precipitation of gamma/gamma . The results of this study will (i) shed light on microstructure evolution during the EBM process with regard to thermal history; and (ii) deepen the current understandings of solidification metallurgy for additive manufacturing of Ni-base superalloys. (C) 2018 Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2018
    Keywords
    Electron beam melting; Inconel 718; Laves; Solidification; In-situ annealing; Thermal history
    National Category
    Manufacturing, Surface and Joining Technology
    Identifiers
    urn:nbn:se:liu:diva-153669 (URN)10.1016/j.matdes.2018.09.006 (DOI)000453008100023 ()
    Note

    Funding Agencies|Sandvik Machining Solutions AB in Sandviken, Sweden; Linkoping University [SFO-MAT-LiU#2009-00971]; Chinese Scholarship Council; Agora Materiae; Swedish Governmental Agency for Innovation Systems (Vinnova) [2016-02675]

    Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-11-07
    3. Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments
    Open this publication in new window or tab >>Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments
    2018 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 713, p. 294-306Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 produced by selective laser melting (SLM) has been characterized with focus on the microstructure, the dependence of sample orientation on the mechanical properties and the effects of post heat treatments. The as-manufactured IN718 has a very fine cellular-dendritic structure with fine Laves phases precipitating in the interdendritic region, and electron backscatter diffraction (EBSD) analysis shows that both the vertically and horizontally built samples have relatively weak texture. The vertically built samples show lower tensile strength but higher ductility than the horizontally built samples, and the mechanism is shown to be partly due to the crystallographic feature but more importantly due to the different amount of residual stress and dislocations accumulated in these two kinds of samples. Applying heat treatments can significantly increase the strength while decrease the ductility correspondingly, and difference in yield strength between the vertically and horizontally built samples decreases with increasing the heat treatment temperatures, mainly due to the removal of residual stress and dislocations.

    Place, publisher, year, edition, pages
    ELSEVIER SCIENCE SA, 2018
    Keywords
    Selective laser melting; Nickel based superalloy; Microstructure; Mechanical properties; Crystallographic orientation; Residual stress
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-145799 (URN)10.1016/j.msea.2017.12.043 (DOI)000425557900036 ()
    Note

    Funding Agencies|Siemens AG in Berlin, Germany [IN718]; Linkoping University [2009-00971]; Chinese Scholarship Council; Agora Materiae

    Available from: 2018-03-22 Created: 2018-03-22 Last updated: 2019-12-01
    4. On the dwell-fatigue crack propagation behavior of a high strength superalloy manufactured by electron beam melting
    Open this publication in new window or tab >>On the dwell-fatigue crack propagation behavior of a high strength superalloy manufactured by electron beam melting
    2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 760, p. 448-457Article in journal (Refereed) Published
    Abstract [en]

    To demonstrate the reliability of additively manufactured superalloys for critical turbine engine components, dynamic tests simulating in-service condition are required. The present study aims to study the dwell-fatigue crack propagation behaviors of IN718 manufactured via electron beam melting (EBM). The textured and columnar-grained microstructure of EBM IN718 shows anisotropic dwell-fatigue cracking resistance when loading axis is aligned parallel and perpendicular to the columnar grains. High and low angle grain boundaries interact differently with the dwell-fatigue cracking path. The effect of different heat treatments on the cracking behavior is also discussed. The dwell-fatigue crack propagation rate of EBM IN718 is compared with forged IN718 under both dwell-fatigue test condition and pure fatigue test condition. The superiority of dwell-fatigue cracking resistance of EBM IN718 to forged IN718 is shown and discussed.

    Place, publisher, year, edition, pages
    ELSEVIER SCIENCE SA, 2019
    Keywords
    IN718; Electron beam melting (EBM); Dwell; Fatigue; Crack propagation
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-159148 (URN)10.1016/j.msea.2019.06.013 (DOI)000474501200044 ()
    Note

    Funding Agencies|Sandvik Machining Solutions AB in Sandviken, Sweden; Chinese Scholarship Council; Swedish Governmental Agency for Innovation Systems (Vinnova) [2016-05175]; Faculty grant SFO-MAT-LiU at Linkoping University [2009-00971]; Agora Materiae

    Available from: 2019-07-30 Created: 2019-07-30 Last updated: 2019-11-07
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  • 42.
    Deng, Dunyong
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Engineering Materials.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 713, p. 294-306Article in journal (Refereed)
    Abstract [en]

    Inconel 718 produced by selective laser melting (SLM) has been characterized with focus on the microstructure, the dependence of sample orientation on the mechanical properties and the effects of post heat treatments. The as-manufactured IN718 has a very fine cellular-dendritic structure with fine Laves phases precipitating in the interdendritic region, and electron backscatter diffraction (EBSD) analysis shows that both the vertically and horizontally built samples have relatively weak texture. The vertically built samples show lower tensile strength but higher ductility than the horizontally built samples, and the mechanism is shown to be partly due to the crystallographic feature but more importantly due to the different amount of residual stress and dislocations accumulated in these two kinds of samples. Applying heat treatments can significantly increase the strength while decrease the ductility correspondingly, and difference in yield strength between the vertically and horizontally built samples decreases with increasing the heat treatment temperatures, mainly due to the removal of residual stress and dislocations.

  • 43.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    A comparison study of the dwell-fatigue behaviours of additive and conventional IN718: The role of dislocation substructure on the cracking behaviour2020In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 797, article id 140072Article in journal (Refereed)
    Abstract [en]

    The dwell-fatigue responses of high temperature materials, such as IN718, manufactured via additive manufacturing processes with different microstructures is of practical interest in terms of time-dependent cracking resistance at elevated temperature. In the present study, the dwell-fatigue cracking behaviours of IN718 manufactured via selective laser melting (SLM) with different heat treatments, and via electron beam melting (EBM) with different scanning strategies were compared at 550 degrees C and with a long 2160 s dwell-holding period. Comparison has also been made with a conventional forged counterpart. Detailed microstructure characterizations have been done to correlate the role of dislocation substructures on the dwell-fatigue damage mechanisms and cracking resistances. A mechanism regarding the susceptibility of the dislocation cell substructure in SLM materials to creep damage is proposed. In addition, the effects of other microstructure features on the dwell cracking resistance are also discussed.

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  • 44.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    On the dwell-fatigue crack propagation behavior of a high strength superalloy manufactured by electron beam melting2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 760, p. 448-457Article in journal (Refereed)
    Abstract [en]

    To demonstrate the reliability of additively manufactured superalloys for critical turbine engine components, dynamic tests simulating in-service condition are required. The present study aims to study the dwell-fatigue crack propagation behaviors of IN718 manufactured via electron beam melting (EBM). The textured and columnar-grained microstructure of EBM IN718 shows anisotropic dwell-fatigue cracking resistance when loading axis is aligned parallel and perpendicular to the columnar grains. High and low angle grain boundaries interact differently with the dwell-fatigue cracking path. The effect of different heat treatments on the cracking behavior is also discussed. The dwell-fatigue crack propagation rate of EBM IN718 is compared with forged IN718 under both dwell-fatigue test condition and pure fatigue test condition. The superiority of dwell-fatigue cracking resistance of EBM IN718 to forged IN718 is shown and discussed.

  • 45. Deng, JN
    et al.
    Bouzy, E
    Fundenberger, JJ
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    He, CS
    Zhang, Z F
    Shenyang National Laboratory for Materials Science, Inst of Metal Research, Chinese Academy of Sciences, Shenyang, China.
    Yang, Yanling
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Textures and local textures in severely cold-rolled and annealed ultra-fine-grained FeCo alloy2005In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 495-497, p. 731-736Article in journal (Refereed)
    Abstract [en]

    We find that a severely rolled FeCo alloy has anomalous enhancement of the rotated-cube {100}< 011 > texture component and a decrease of the {111} components after annealing, which is contrast to the recrystalliization behaviors reported in traditional BCC metals and alloys. The local texture measurements show that two kinds of grains with obviously different orientations, i.e. {100} and {111}, are heterogeneously distributed in the deformed specimen and the migration of high-angle grain boundaries is observed after annealing in the disordering temperature region.

  • 46.
    Deng, Lin-Long
    et al.
    Xiamen Univ, Peoples R China.
    Xie, Su-Yuan
    Xiamen Univ, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Fullerene-Based Materials for Photovoltaic Applications: Toward Efficient, Hysteresis-Free, and Stable Perovskite Solar Cells2018In: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 4, no 10, article id 1700435Article in journal (Refereed)
    Abstract [en]

    Perovskite solar cells are promising candidates for next-generation photovoltaics. Fullerenes and their derivatives can act as efficient electron transport layers, interfacial modification layers, and trap state passivators in perovskite solar cells, all of which play an important role in increasing efficiency, reducing current hysteresis, and enhancing device stability. Herein, recent progress in the use of fullerenes and their derivatives in perovskite solar cells is reviewed, with a particular emphasis on fullerene chemical structures that affect device performance. Potential fullerene candidates that could further improve device performance and stability are also discussed.

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  • 47.
    Dippo, Olivia F.
    et al.
    Univ Calif San Diego, CA 92093 USA.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Wenger, Emma
    Univ Calif San Diego, CA 92093 USA.
    Vecchio, Kenneth S.
    Univ Calif San Diego, CA 92093 USA; Univ Calif San Diego, CA 92093 USA.
    Color and pseudogap tunability in multicomponent carbonitrides2022In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 217, article id 110600Article in journal (Refereed)
    Abstract [en]

    The design and tailoring of material color for both aesthetic and functionality is an ongoing topic of materials science and engineering research. In this work, a method is developed to tune and predict color and pseudogap energy of any compositional variation of B1-rocksalt structured Group 4 and 5 transition metal carbonitride. Optical properties of bulk multicomponent transition metal carbonitrides were characterized using reflectivity spectra. Optical pseudogap energies were extrapolated using the Tauc method, and color appearance was quantified in the Commission Internationale de lEclairage (CIE) Lightness*Chroma*hue (L*C*h) color space. Variations of color parameters chroma and hue were analyzed in terms of pseudogap energies and electronic band structures. Compositional variations were utilized to predictably tune aspects of the electronic structure, including the specificity of electronic transitions and the energy at which they occur, to tailor the materials color appearance and facilitate the formation of new carbonitride colors.

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  • 48.
    Dongo, Patrice D.
    et al.
    ATM Univ libre Bruxelles, Belgium.
    Håkansson, Anna
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Stoeckel, Marc-Antoine
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pavlopolou, Eleni
    Fdn Res & Technol Hellas, Greece.
    Wang, Suhao
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Farina, Dario
    ATM Univ libre Bruxelles, Belgium.
    Queeckers, Patrick
    ATM Univ libre Bruxelles, Belgium.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Iorio, Carlo Saverio
    ATM Univ libre Bruxelles, Belgium.
    Crispin, Reverant
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Detection of Ice Formation With the Polymeric Mixed Ionic-Electronic Conductor PEDOT: PSS for Aeronautics2023In: Advanced Electronic Materials, E-ISSN 2199-160XArticle in journal (Refereed)
    Abstract [en]

    Ice formation detection is important in telecommunications and aeronautics, e.g., ice on the wings of an aircraft affects its aerodynamic performance and leads to fatal accidents. While many types of sensors exist, resistive sensors for ice detection have been poorly explored. They are however attractive because of their simplicity and the possibility to install an array of sensors on large areas to map the ice formation on wings. Hygroscopic ionic conductors have been demonstrated for resistive ice sensing but their high resistance prevents the readout of sensor arrays. In this work, mixed ionic-electronic polymer conductors (MIEC) are considered for the first time for ice detection. The polymer blend poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is solution deposited on a pair of electrodes. The sensor displays an abrupt rise in electrical resistance during the transition phase between water liquid to solid. It is proposed that the morphology and electronic transport in PEDOT are affected by the freezing event because the absorbed water in the PSS-rich phase undergoes dilatation upon forming ice crystals. For the aeronautics application, successful tests of integration of sensing layer in pre-preg layers of aeronautical grade and freezing detection are carried out to validate the ice detection principle.

  • 49.
    Du, Yong
    et al.
    Shanghai Inst Technol, Peoples R China.
    Chen, Jiageng
    Shanghai Inst Technol, Peoples R China.
    Meng, Qiufeng
    Shanghai Inst Technol, Peoples R China.
    Xu, Jiayue
    Shanghai Inst Technol, Peoples R China.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Paul, Biplab
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Flexible Thermoelectric Double-Layer Inorganic/Organic Composites Synthesized by Additive Manufacturing2020In: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 6, no 8, article id 2000214Article in journal (Refereed)
    Abstract [en]

    This study shows an approach to combine a high electrical conductivity of one composite layer with a high Seebeck coefficient of another composite layer in a double-layer composite, resulting in high thermoelectric power factor. Flexible double-layer-composites, made from Bi2Te3-based-alloy/polylactic acid (BTBA/PLA) composites and Ag/PLA composites, are synthesized by solution additive manufacturing. With the increase in Ag volume-ratio from 26.3% to 41.7% in Ag/PLA layers, the conductivity of the double-layer composites increases from 12 S cm(-1)to 1170 S cm(-1), while the Seebeck coefficient remains approximate to 80 mu V K(-1)at 300 K. With further increase in volume ratio of Ag until 45.6% in Ag/PLA composite layer, the electrical conductivity of the double-layer composites increases to 1710 S cm(-1), however, with a slight decrease of the Seebeck coefficient to 64 mu V K-1. The electrical conductivity and Seebeck coefficient vary only to a limited extent with the temperature. The high Seebeck coefficient is due to scattering of low energy charge carriers across compositionally graded interfaces. A power factor of 875 mu W m(-1) K(-2)is achieved at 360 K for 41.7 vol.% Ag in the Ag/PLA layers. Solution additive manufacturing can directly print this double-layer composite into intricate geometries, making this process is promising for large-scale fabrication of thermoelectric composites.

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  • 50.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Univ Illinois, IL 61801 USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Elastic properties and plastic deformation of TiC- and VC-based alloys2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 144, p. 376-385Article in journal (Refereed)
    Abstract [en]

    Transition-metal (TM) carbides are an important class of hard, protective coating materials; however, their brittleness often limits potential applications. We use density functional theory to investigate the possibility of improving ductility by forming pseudobinary cubic (MMC)-M-1-C-2 alloys, for which M-1 = Ti or V and M-2 = W or Mo. The alloying elements are chosen based on previous results showing improved ductility of the corresponding pseudobinary nitride alloys with respect to their parent compounds. While commonly-used empirical criteria do not indicate enhanced ductility in the carbide alloys, calculated stress/strain curves along known slip systems, supported by electronic structure analyses, indicate ductile behavior for VMoC. As VMoC layers are sheared along the 1 (1) over bar0 direction on {111} planes, the stress initially increases linearly up to a yield point where the accumulated stress is partially dissipated. With further increase in strain, the stress increases again until fracture occurs. A similar mechanical behavior is observed for the corresponding TM nitride VMoN, known to be a ductile ceramic material [1]. Thus, our results show that VMoC is a TM carbide alloy which may be both hard and ductile, i.e. tough. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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