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  • 1.
    Andersson, Nils-Eric
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue crack growth rate in commercial thick plates of AA7010Manuscript (preprint) (Other academic)
    Abstract [en]

    A mapping of fatigue crack growth rates in commercial thick plates of a high strength aluminium alloy, AA7010-T7451/52, has been done. The investigated plate thicknesses were 100, 150 and 200 mm. Material from near edge and mid-width at near surface and mid-thickness has been investigated. Measurements of crack length have been perfonned using DC potential drop. Cyclic condensation is used in order to be able to investigate local crack growth after fracture. Influence of crack closure, crack branching and slow growing side cracks on fatigue crack growth rate of S-L and L-T oriented CT specimens are discussed. S-L specimens show the highest fatigue crack growth rates. Beach marks on the fracture surface due to the cyclic condensation reveals locally straight crack fronts. A difference in growth rate between near surface and mid-thickness positioned L-T specimens are found. At a nominal ΔK of - 7 MPa√m the mid-thickness samples showed a sudden crack growth rate acceleration. The result of the investigation is explained in tenns of variations in structure, which is a function of position in the plates and plate thickness.

  • 2.
    Andersson, Nils-Eric
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue crack growth rate in thick plates of 70101999In: Fatigue 99: Proceedings of the 7th International Fatigue Conference / [ed] X. R. Wu, 1999Conference paper (Refereed)
  • 3.
    Andersson, Nils-Eric
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Property comparison of thin walled sections machined using high speed machining and conventional machiningManuscript (preprint) (Other academic)
    Abstract [en]

    The influence of two different machining concepts has been compared. Pockets were machined in a thick plate of AA7010-T7451 by using a high speed machining concept at three different cutting speeds and a conventional machining concept. The pockets were machined using down cut milling and of the remaining thin walls of material fatigue samples were taken out. Some high-speed machined surfaces were anodized using chromic acid in order to see if differences in fatigue properties remained after this surface process. Fatigue properties at constant amplitude and random spectra loading were tested. Properties like residual stress, surface roughness; peak broadening at grazing incidence and micro hardness of machined surfaces were investigated and correlated to the fatigue results. A low cutting speed using the high speed machining or the conventional machining concept yielded the best fatigue properties when fatigue initiation is of concern. The higher fatigue strength is not explained by the residual stresses measured at the machined surfaces using chromium and copper radiation or by the somewhat larger surface roughness. The penetration depth of the residual stresses was found to be higher at high cutting speeds. Fatigue initiation took most often place at near surface iron-rich inclusions. The points of fatigue initiation were not found to differ for different machining concepts and cutting speeds.

  • 4.
    Andersson, Nils-Eric
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Through thickness fracture toughness variations of AA7021 thick plateManuscript (preprint) (Other academic)
    Abstract [en]

    In this work, a variation of fracture toughness as a function of position and orientation in commercial thick plates of a high strength aluminium alloy has been investigated. Structural and mechanical property variations have been investigated in order to understand the result of the fracture toughness measurements. 100, 150 and 200 mm thick plates of the aluminium alloy AA7010 were studied. The material was averaged and stress relieved by stretching (100 and 150 mm) and cold compression (200 mm), T7451/52. The material studied is frequently used to produce load-carrying airframe components. The knowledge of fracture properties throughout the thick plates is of importance since components are machined from them. The understanding of the varying fracture properties is valuable for development of material and or processes for producing thick plate of high strength aluminium alloys. It is of course also important to know the limitations of the thick plate material and the best way to produce a certain component from a piece of the plate material. Investigated parameters influencing fracture properties are inclusions, recrystallisation, yield strength, chemical composition and quench rate.

  • 5.
    Andersson, Nils-Eric
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Björklund, Stefan
    Linköping University, Department of Mechanical Engineering, Production Engineering. Linköping University, The Institute of Technology.
    Face milling of AA7010 at high cutting speedsManuscript (preprint) (Other academic)
    Abstract [en]

    Face milling using different commercial tools and inserts at varying cutting speeds on a high strength aluminium alloy has been performed. The surface integrity of the machined samples has been investigated in terms of surface roughness, residual stresses, hardness and peak broadening from x-ray diffraction at grazing angle incidence. Some fatigue testing of the machined surfaces has been done. The cutting chips from the different machining parameters are investigated and compared to one another. The results show a strong influence of tool insert on surface roughness, residual stress, peak broadening, and hardness profile and fatigue properties. The influence of cutting speed on the surface integrity is much smaller. The cutting speed does however influence the size and shape of the cutting chips. There is also a general decrease in peak broadening from x-ray diffraction very near the machined surface after high cutting speeds. This could be explained by a higher local heating of the work piece at very high cutting speeds.

  • 6.
    Andersson, Nils-Eric
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zeng, Xiao-Hu
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The influence of hot rolling on the variation of through thickness structure of AA7010 thick plates1996In: Thermomechanical processing in theory, modelling and practice [TMP]2: proceedings of an International Conference organised in celebration of the 75th anniversary of the Swedish Society for the Materials Technology, 1996, 284-289 p.Conference paper (Other academic)
    Abstract [en]

    The variation of through thickness structure and yield strength of AA7010-T7451 thick plate has been investigated. Grain sizes at different depths were determined qualitatively by using optical microscopy. Texture measurements were carried out using X-ray technique at the same depths as grain size studies and tensile property tests have been performed. EBSP techdque has been used to compare the degree of recovered and recrystallized grain structure at different depths. Tensile testing determined through thickness variations in yield strength. The well known W shape of longitudinal yield strength variation through the thickness was not observed. The influence of texture on the yield strength measured is discussed.

  • 7.
    Brodin, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Andersson, Olov
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Mechanical Behaviour and Microstructure Correlation in a Selective Laser Melted Superalloy2013In: ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, American Society of Mechanical Engineers (ASME) , 2013, Vol. 5A, 1-7 p.Conference paper (Refereed)
    Abstract [en]

    Selective laser melting (SLM), or, as the industry standard denotes the process, laser sintering, is an additive manufacturing process where metal powder is melted by a laser source layer-wise, forming a solid, dense metallic component. With the SLM process, near net shape components can be manufactured directly from a CAD model. The model is sliced into thin (max 100μm thick) layers. Powder is spread onto a metallic build platform and the powder is fused by a laser as dictated by the CAD model. The laser energy is intense enough to permit full melting (welding) of the particles to form solid metal. The process is repeated layer by layer until the part is complete.

    A number of materials are available, including steel, aluminium, titanium and, in recent time, also superalloys. The material investigated in the current project is an alloy in agreement with the composition of Haynes International Hastelloy X, a solution strengthened superalloy typically used in large welded components exposed to high temperatures in oxidizing as well as reducing environments.

    Microstructurally, the material is different from both a hot-rolled, as well as a cast material due to the manufacturing process. Since the SLM process involves laser melting of powder particles in the size range of <50μm, the structure resembles of a weld structure, however on a smaller scale. Due to the layer-by-layer build strategy, the material will exhibit anisotropy. Different heat treatment approaches can be adopted in order to homogenize the material and to minimize the effect of anisotropy. A stress relieve heat treatment was adopted and compared to the findings of the as manufactured SLM material.

    The current project focuses on evaluating mechanical properties for a material manufactured by the SLM process and comparing to data for established manufacturing processes. For evaluation of the mechanical properties, low cycle fatigue testing and tensile testing has been performed. The microstructure and material deformation / cracking are evaluated by light optical microscopy and SEM, where electron backscatter diffraction is used. Due to the weld-like structure, the material will be transversely isotropic in the as-manufactured condition with one symmetry plane perpendicular to the build direction. Any direction perpendicular to the build direction tends to give increased strength compared to a direction parallel to the build direction if monotonic data are concerned. If fatigue properties are concerned, the anisotropy is also obvious. It is shown that the differences in behaviour can be coupled to microstructure.

  • 8.
    Brodin, Håkan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Eriksson, Robert
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Finite Element Modelling and Damage Evaluation of Air Plasma Sprayed Thermal Barrier Coatings2012Conference paper (Refereed)
  • 9.
    Brodin, Håkan
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Jinnestrand, Magnus
    ProTang Mekanikkonsulter AB Västerås.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Siemens Industrial Turbomachinery AB Finspång.
    Thermal Barrier Coating Fatigue Life Assessment2006In: Fatigue 2006, 2006Conference paper (Refereed)
  • 10.
    Brodin, Håkan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Influence on low cycle fatigue properties of bond coat oxidation for a thermal barrier coating2001In: 10th International Congres of Fracture,2001, 2001Conference paper (Refereed)
  • 11.
    Brodin, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Damage development in two thermal barrier coating systems2009In: ICF12,2009, 2009Conference paper (Other academic)
    Abstract [en]

          

  • 12.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Sandviken, Sweden.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan J.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Characterization of austenitic stainless steels deformed at elevated temperature2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 10, 4525-4538 p.Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology,Sandviken, 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.
    Creep and Fatigue Interaction Behavior in Sanicro 25 Heat Resistant Austenitic Stainless Steel2016In: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 69, no 2, 337-342 p.Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Johansson, Sten
    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.
    Damage and Fracture Behaviours in Advanced Heat Resistant Materials During Slow Strain Rate Test at High Temperature2013Conference paper (Other academic)
    Abstract [en]

    As a renewable energy resource, biomass or biomass co-firing in coal-fired power plants with high efficiency are desired which corresponding to elevated temperature and high pressure. An upgrade of the material performance to austenitic stainless steels is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. These materials suffer from creep and fatigue damage during the service. In this study, these behaviours are evaluated using slow strain rate testing (SSRT) with strain rate down to 1*10-6/s at temperature up to 700°C. The influence of temperature and strain rate on strength and ductility in one austenitic stainless steel and one nickel base alloys are investigated. The damage and fracture due to the interaction between moving dislocations and precipitates are studied using electron channelling contrast imaging (ECCI) and electron backscattering diffraction (EBSD). The deformation and damage mechanisms active during SSRT are essentially the same as under creep. The influence of dynamic strain ageing (DSA) phenomena that appears in the tested temperature and strain rate regime is also discussed, DSA is intensified by increased temperature and decreased strain rate.

  • 15.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Johansson, Sten
    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.
    Damage and Fracture Behaviours in Aged Austentic Materials During High-Temperature Slow Strain Rate Testing2014Conference paper (Refereed)
    Abstract [en]

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

  • 16.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    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.
    Deformation and damage behaviours of austenitic alloys in the dynamic strain ageing regimeManuscript (preprint) (Other academic)
    Abstract [en]

    Deformation and damage behaviours influenced by dynamic strain ageing (DSA) in three austenitic stainless steels and two nickel-base alloys have been investigated using tensile tests at elevated temperatures. The deformation and damage behaviours have been analysed using electron channeling contrast imaging and electron backscatter diffraction. The results from this study show that DSA not always reduce ductility, in fact for some materials the ductility can increase in the DSA regime. This is attributed to the formation of nano twins by DSA stimulated twinning induced plasticity. Damage mechanisms due to DSA were also investigated and discussed.

  • 17.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Johansson, Sten
    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.
    Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature2014In: Theoretical and Applied Mechanics Letters, ISSN 2095-0349, Vol. 4, no 041004Article in journal (Refereed)
    Abstract [en]

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

  • 18.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    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.
    Influence of deformation rate on mechanical response of an AISI 316L austenitic stainless steel2014In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 922, 49-54 p.Article in journal (Refereed)
    Abstract [en]

    Austenitic stainless steels are often used for components in demanding environment. These materials can withstand elevated temperatures and corrosive atmosphere like in energy producing power plants. They can be plastically deformed at slow strain rates and high alternating or constant tensile loads such as fatigue and creep at elevated temperatures. This study investigates how deformation rates influence mechanical properties of an austenitic stainless steel. The investigation includes tensile testing using strain rates of 2*10-3/ and 10-6/s at elevated temperatures up to 700°C. The material used in this study is AISI 316L. When the temperature is increasing the strength decreases. At a slow strain rate and elevated temperature the stress level decreases gradually with increasing plastic deformation probably due to dynamic recovery and dynamic recrystallization. However, with increasing strain rate elongation to failure is decreasing. AISI 316L show larger elongation to failure when using a strain rate of 10-6/s compared with 2*10-3/s at each temperature. Electron channelling contrast imaging is used to characterize the microstructure and discuss features in the microstructure related to changes in mechanical properties. Dynamic recrystallization has been observed and is related to damage and cavity initiation and propagation.

  • 19.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    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.
    Influence of Dynamic Strain Ageing on Damage in Austenitic Stainless Steels2012Conference paper (Other academic)
  • 20.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, sweden.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of High Temperature Ageing on the Toughness of Advanced Heat Resistant Materials2013Conference paper (Refereed)
    Abstract [en]

    Advanced biomass, biomass co-firing in coal-fired and future advanced USC coal-fired power plants with high efficiency require the materials to be used at even higher temperature under higher pressure. The reliability and integrity of the material used are therefore of concern. In this study, the influence of ageing at temperatures up to 700°C for up to 3 000 hours on the toughness of two advanced heat resistant austenitic steels and one nickel alloy are investigated. The influence on toughness due to differences in the chemical composition as well as the combined effect of precipitation and growth of the precipitates has been analysed by using SEM techniques. The fracture mechanisms that are active for the different ageing treatments are identified as a function of temperature and time. Local approach methods are used to discuss the influence of the precipitation and growth of precipitates on the toughness or fracture in  the different aged materials.

  • 21.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Johansson, Sten
    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.
    Long Term High-Temperature Environmental Effect on Impact Toughness in Austenitic Alloys2015In: / [ed] Key Engineering Materials Vol 627 (2015),pp 205-208., 2015, 205-308 p.Conference paper (Refereed)
  • 22.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Strategy research, SE-81181 Sandviken, Sweden.
    Johansson, Sten
    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.
    Mechanical behaviors of alloy 617 with varied strain rates at high temperatures2014In: THERMEC 2013, Trans Tech Publications Ltd , 2014, Vol. 783-786, 1182-1187 p.Conference paper (Refereed)
    Abstract [en]

    Nickel base alloys due to their high performances have been widely used in biomass and coal fired power plants. They can undertake plastic deformation with different strain rates such as those typically seen during creep and fatigue at elevated temperatures. In this study, the mechanical behaviors of Alloy 617 with strain rates from 10-2/s down to 10-6/s at temperatures of 650C and 700C have been studied using tensile tests. Furthermore, the microstructures have been investigated using electron backscatter detection and electron channeling contrast imaging. At relatively high strain rate, the alloy shows higher fracture strains at these temperatures. The microstructure investigation shows that it is caused by twinning induced plasticity due to DSA. The fracture strain reaches the highest value at a strain rate of 10-4/s and then it decreases dramatically. At strain rate of 10-6/s, the fracture strain at high temperature is now smaller than that at room temperature, and the strength also decreases with further decreasing strain rate. Dynamic recrystallization can also be observed usually combined with crack initiation and propagation. This is a new type of observation and the mechanisms involved are discussed. © (2014) Trans Tech Publications, Switzerland.

  • 23.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    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.
    Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures2014In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 783-786, 1182-1187 p.Article in journal (Refereed)
    Abstract [en]

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

  • 24.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Siemens Industrial Turbomachinery AB, Berlin.
    Chai, Guocai
    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.
    Högberg, Jan
    AB Sandvik Materials Technology R&D Center Sandviken.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Local Surface Phase Stability During Cyclic Oxidation Process2017In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 879, 855-860 p.Article in journal (Refereed)
  • 25.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Chai, Guocai
    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.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Influence of Cyclic Oxidation in Moist Air on Surface Oxidation-Affected Zones2017Conference paper (Refereed)
  • 26.
    Calmunger, Mattias
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Engineering Materials.
    Eriksson, Robert
    Siemens AG, Huttenstr. 12, 10553 Berlin, Germany.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandviken, 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.
    Surface Phase Transformation in Austenitic Stainless Steel Induced by Cyclic Oxidation in Humidified Air2015In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 100, 524-534 p.Article in journal (Refereed)
    Abstract [en]

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

  • 27.
    Calmunger, Mattias
    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.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Sandviken, Sweden.
    Characterisation of creep deformation during slow strain rate tensile testing2015Manuscript (preprint) (Other academic)
    Abstract [en]

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

  • 28.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Johansson, Sten
    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.
    Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM2014Conference paper (Refereed)
    Abstract [en]

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

  • 29.
    Ceschini, Lorella
    et al.
    Dept of Industrial Engineering (DIN), University of Bologa, Italy.
    Morri, Alessandro
    Dept of Industrial Engineering (DIN), University of Bologa, Italy.
    Morri, Andrea
    Industrial Research Centre for Advanced Mechanics and Materials, University of Bologna, Italy.
    Toschi, Stefania
    Dept of Industrial Engineering (DIN), University of Bologna, Italy.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Seifeddine, Salem
    Dept of Materials and Manufacturing, Jönköping University.
    Effect of Microstructure and Overaging on the Tensile Behavior at Room and Elevated Temperature of C355-T6 Cast Aluminum Alloy2015In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 83, 626-634 p.Article in journal (Refereed)
    Abstract [en]

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

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

  • 30.
    Ceschini, Lorella
    et al.
    Dept of Industrial Engineering (DIN), University of Bologa, Italy.
    Morri, Alessandro
    Dept of Industrial Engineering (DIN), University of Bologna, Italy.
    Toschi, Stefania
    Dept of Industrial Engineering (DIN), University of Bologna, Italy.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Seifeddine, Salem
    Dept of Materials and Manufacturing, Jönköping University.
    Microstructural and Mechanical Properties Characterization of Heat Treated and Overaged Cast A354 Alloy with Various SDAS at Room and Elevated Temperature2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 648, 340-349 p.Article in journal (Refereed)
    Abstract [en]

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

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

  • 31.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Strategy research, Sandviken, Sweden.
    Calmunger, Mattias
    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.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Odqvist, Joakim
    Sandvik Materials Technology, Strategy research, Sandviken, Sweden.
    Influence of Dynamic Strain Ageing and Long Term Ageing on Deformation and Fracture Behaviors of Alloy 6172016In: THERMEC 2016 / [ed] C. Sommitsch, M. Ionescu, B. Mishra, E. Kozeschnik and T. Chandra, Trans Tech Publications, 2016, Vol. 879, 306-311 p.Conference paper (Refereed)
    Abstract [en]

    Influences of dynamic strain ageing and long term ageing on deformation, damage and fracture behaviors of Alloy 617 material have been studied. Dynamic strain ageing can occur in this alloy at temperature from 400 to 700°C, which leads to a strain hardening and also an increase in fracture strain due to plastic deformation caused by twinning. Long term ageing at 700°C for up to 20 000 hours can cause different precipitation such as γ ́, M6C (Mo-rich) and M23C6 (Cr-rich) carbides. These carbides are both inter-and intra-granular particles. The long term ageing reduces the fracture toughness of the material, but the alloy can still have rather high impact toughness and fracture toughness even with an ageing at 700°C for 20 000 hour. The mechanisms have been studied using electron backscatter detection and electron channeling contrast imaging. It shows that besides dislocation slip, twinning is another main deformation mechanism in these aged Alloy 617 materials. At the crack front, plenty of micro or nanotwins can be observed. The formation of these twins leads to a high ductility and toughness which is a new observation or a new concept for this type of material.

  • 32.
    Chai, Guocai
    et al.
    RD Centre Sandvik Materials Technology, Sandviken.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Transitions of Faatigue Crack Initgiation from Surface, Subsurface to SNDFCO2006In: ECF16 16th European Conference of Fracture,2006, 2006Conference paper (Refereed)
  • 33.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Kivisäkk, Ulf
    Sandvik Materials Technology, R&D Centre, Sandviken, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hydrogen Induced Stress Cracking Behavior in Duplex Stainless Steels2013Conference paper (Other academic)
  • 34.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue Behaviors in Duplex Stainless Steel Studied Using In-Situ SEM-EBSD Method2014In: Procedia Materials Science, ISSN 2211-8128, Vol. 3, 1748-1753 p.Article in journal (Refereed)
    Abstract [en]

    Austenite and ferrite in duplex stainless steels have different physical and mechanical properties. They can behave different during cyclic loading. To understand the fatigue behaviors of these two phases, an in-situ SEM/EBSD fatigue test has been performed. Flat specimens made from the specimens of pre-fatigue tested with three point bending were cyclically loaded in a scanning electron microscope via a compact test rig. By in situ/ex situ SEM/EBSD examination, slip activities and propagation of the fatigue cracks have been studied. Microstructures along the path of the fatigue crack were characterized. The different phase properties seem to lead to certain difference in the slip activity and formation of PSBs. Inhomogeneous slip activities and local strain concentrations were also found, which developed with increasing number of load cycles. Crack propagation behaviors in grain and cross the grain or phase boundaries have been discussed. Crack deflection occurs at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection and formation of crack branches can significantly reduce the crack propagation rate.

  • 35.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Micro Fatigue Crack Propagation Behavior in a Duplex Stainless Steel Studied Using In Situ SEM/EBSD Method2014In: 11TH INTERNATIONAL FATIGUE CONGRESS, PTS 1 AND 2, Trans Tech Publications Inc., 2014, Vol. 891-892, 313-318 p.Conference paper (Refereed)
    Abstract [en]

    Fatigue crack propagation behaviors in a duplex stainless steel have been studied using an in-situ SEM/EBSD fatigue test and a conventional da/dN test. Crack propagation behaviors in grain, effect of Schmid factor, propagation cross the grain or phase boundaries have been discussed. Crack propagation occurs mainly in the grains with a high Schmid factor, but with very small Schmid factor. Crack deflection occurs mainly at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection can lead to a decrease in crack propagation rate. Formation of crack branches can significantly reduce the crack propagation rate, which can cause crack growth retardation in the main crack path in the worst case. The crack branches formed are usually not ideal. They can propagate almost transversely to the main crack direction with a mode II stress intensity factor, SIF, and a rate that is much higher than that of the main crack.

  • 36.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Kivisäkk, Ulf
    Sandvik Materials Technology, R&D Centre, Sandviken.
    Hydrogen Induced Stress Cracking in Heterogeneous Materials2012Conference paper (Other academic)
  • 37. Chai, Guocai
    et al.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Slamecka, Karel
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Fatigue Crack Branching Behavior in Dual Phase Material2009Conference paper (Other academic)
    Abstract [en]

    Fatigue crack branching behaviour in a dual phase steel has been investigated using an in-situ SEM/EBSD fatigue test and a conventional da/dN test. Crack branching results mainly from the extrusions and intrusions of slip bands developed in the grains. The number of crack branches formed depends strongly on the loading condition and the microstructure of the material. The in-situ observation confirms that the formation of crack branches can significantly reduce the crack propagation rate that leads to crack growth retardation in the main mode I crack path. The crack branches formed are usually not ideal. They can propagate almost transversely to the main crack direction with a mode II stress intensity factor, SIF, and a rate that is much higher than that of the main crack.

  • 38.
    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)
  • 39.
    Chai, Guocai
    et al.
    Sandvik Mat Technology.
    Ronneteg, Sabina
    Sandvik Mat Technology.
    Kivisakk, Ulf
    Sandvik Mat Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Mechanisms of Hydrogen Induced Stress Crack Initiation and Propagation in Super Duplex Stainless Steels2009In: STEEL RESEARCH INTERNATIONAL, ISSN 1611-3683, Vol. 80, no 7, 482-487 p.Article in journal (Refereed)
    Abstract [en]

    Austenitic and ferritic duplex stainless steels, DSS, have recently suffered from hydrogen stress induced cracking, HISC, in subsea components with a cathodic protection. This paper provides discussions on possible HISC mechanisms. HISC initiation can occur at the ferritic grain boundaries and phase boundaries at a stress lower than the yield strength, but dominantly at phase boundaries at a stress higher than the yield strength. EBSD analysis shows that HISC in DSS results from the interaction between the dynamic plasticity by creep and hydrogen diffusion. A model on the formation of microstresses in these two phases under creep conditions is proposed, which explains why HISC occurs mainly in the ferritic phase. Discontinuous two-dimensional HISC paths were observed. The austenitic phase acts as obstacles for crack propagation. The fracture covers "valleys" and "peaks" with the cleavage ferrite and the austenite with microfacets or striations due to the hydrogen-enhanced localized-plasticity.

  • 40.
    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, 307-310 p.Conference 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.

  • 41.
    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, 158-169 p.Article 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.

  • 42.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Damage analysis of a retired gas turbine disc2014In: Proceedings of the 2014 Energy Materials Conference, John Wiley & Sons, 2014, 405-410 p.Conference paper (Refereed)
    Abstract [en]

    Gas turbine discs operate mostly at high temperature gradients and are subjected to mechanical loads simultaneously. The high thermal and mechanical loads eventually could result in degradation and damages in disc material, thereby increasing the risk of disc failure. In this study, a damage analysis was performed in a retired gas turbine disc made of Inconel 718. Oxidation attack and microstructural degradation as the consequence of the high service temperature have been found to be the main damages that take place in the non-contact area of the retired disc. In the blade/disc contact area, fretting fatigue occurs, with a result that cracks initiate from the oxide/metal interface and propagate in the disc alloy parallel to the sliding direction of fretting, consequently reducing the stability and safety of the disc. Meantime, oxygen diffuses into the fretting fatigue cracks, thereby exacerbating the oxidation attack. A multi-layered scale with periodic formation of the Fe-oxide/spinel layer and the metallic layer is formed on the contact surface. In both contact and non-contact area, recrystallization and α-Cr precipitation take place in the surface layer of the disc alloy. The locations where α-Cr precipitates are commonly considered to be the natural sites for mechanical weakness.

  • 43.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Avdovic, Pajazit
    Siemens Industrial Turbomachinery, Finspång, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Karlsson, Fredrik
    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.
    Analysis of Thermal Effect on Residual Stresses of Broached Inconel 7182014Conference paper (Refereed)
    Abstract [en]

    Inconel 718 is a nickel based superalloy that is widely used as a turbine disc material in gas turbine industries. This study details the effect of thermal exposure on the residual stresses produced when broaching Inconel 718. The chosen parameters for broaching in this study are similar to those used when manufacturing turbine discs. The broaching operation produced a high level of tensile residual stresses at the broached surface. A layer with tensile residual stresses was formed in the sub-surface region, followed by a layer several times thicker with compressive residual stresses. Thermal exposure was conducted at 550 °C. The depth distributions of residual stresses after thermal exposure are presented and discussed in this paper. Complete relaxation of the surface tensile residual stresses was observed after 30 h thermal exposure, whereas the 3000 h thermal exposure influenced both the surface and sub-surface residual stress states.

  • 44.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    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, Sweden.
    Moverare, Johan
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Karlsson, Fredrik
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Effect of thermal exposure on microstructure and nano-hardness of broached Inconel 7182014In: MATEC Web of Conferences Vol. 14 (2014) EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications: Session 8: Recrystallization and Grain Growth / [ed] J.Y. Guédou and J. Choné, Les Ulis, France: E D P Sciences , 2014, 08002-p.1-08002-p.6 p.Conference paper (Refereed)
    Abstract [en]

    Inconel 718 is a high strength, heat resistant superalloy that is used extensively for components in hot sections of gas turbine engines. This paper presents an experimental study on the thermal stability of broached Inconel 718 in terms of microstructure and nano-hardness. The broaching process used in this study is similar to that used in gas turbine industries for machining fir-tree root fixings on turbine discs. Severe plastic deformation was found under the broached surface. The plastic deformation induces a work-hardened layer in the subsurface region with a thickness of ∼50 μm. Thermal exposure was conducted at two temperatures, 550 C and 650 C respectively, for 300 h. Recrystallization occurs in the surface layer during thermal exposure at 550 C and α-Cr precipitates as a consequence of the growth of recrystallized δ phases. More recrystallized grains with a larger size form in the surface layer and the α-Cr not only precipitates in the surface layer, but also in the sub-surface region when the thermal exposure temperature goes up to 650 C. The thermal exposure leads to an increase in nano-hardness both in the work-hardened layer and in the bulk material due to the coarsening of the main strengthening phase γ′′.

  • 45.
    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
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    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, 3664-3676 p.Article 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.

  • 46.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Bushlya, Volodymyr
    Saoubi, Rachid M
    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.
    Effect of Cutting Conditions on Machinability of AD 730 TM during High Speed Turning with PCBN Tools2017Conference paper (Refereed)
  • 47.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund university.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Bushlya, Volodymyr
    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.
    ECCI and EBSD Study of Surbsurface Damages in High Speed Turning of Inconel 718 under Different Tools and Machining Parameters2013Conference paper (Refereed)
  • 48.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Cyclic Hot Corrosion of Thermal Barrier Coatings and Overlay Coatings2013In: Proceedings of ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, GT2013, The American Society of Mechanical Engineers (ASME) , 2013, Vol. 4, 1-8 p.Conference paper (Refereed)
    Abstract [en]

    The influence, and interdependence, of water vapor and Na2SO4–50 mol% NaCl on the oxidation of a NiCoCrAlY coating and a thermal barrier coating (TBC) were studied at 750 °C. Water vapor was found to have a negligible effect on oxide composition, but influenced the oxide morphology on the NiCoCrAlY coating. Na2SO4–50 mol% NaCl deposits on the coatings influencedoxide composition, most notably by the promotion of a Y rich phase. The effect of Na2SO4–50 mol% NaCl deposits was also evident for the TBC coated specimen, where the formed metal/ceramic interface oxide was affected by salt reaching the interface by penetration of the zirconia TBC.

  • 49.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, SE-61283 Finspång, Sweden.
    Fractographic and microstructural study of isothermally and cyclically heat treated thermal barrier coatings2014In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 243, 82-90 p.Article in journal (Refereed)
    Abstract [en]

    The fracture surfaces from adhesion tested thermal barrier coatings (TBC) have been studied by scanning electron microscopy. The adhesion test have been made using the standard method described in ASTM 633, which makes use of a tensile test machine to measure the adhesion. The studied specimens consist of air plasma sprayed (APS) TBC deposited on disc-shaped substrates of Hastelloy X. The bond coat (BC) is of NiCoCrAlY type and the top coat (TC) consists of yttria–stabilised–zirconia. Before the adhesion test, the specimens were subjected to three different heat treatments: 1) isothermal oxidation 2) thermal cycling fatigue (TCF) and 3) burner rig test (BRT). The fracture surfaces of the adhesion tested specimens where characterised. A difference in fracture mechanism were found for the different heat treatments. Isothermal oxidation gave fracture mainly in the top coat while the two cyclic heat treatments gave increasing amount of BC/TC interface fracture with number of cycles. Some differences could also be seen between the specimens subjected to burner rig test and furnace cycling.

  • 50.
    Eriksson, Robert
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Brodin, Håkan
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan.
    Li, Xin-Hai
    Siemens, Industrial Turbomachinery AB, Finspång.
    Fractographic Study of Adhesion Tested Thermal Barrier Coatings Subjected to Isothermal and Cyclic Heat Treatments2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, 195-200 p.Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are used in gas turbines to protect metallic components from high temperature. In the present study adhesion tests have been conducted on APS TBC coated specimens subjected to different heat treatments. Isothermal and cyclic heat treatments have been conducted at temperatures around 1100 °C and the adhesion have been tested using the method described in ASTM C633. The fracture surfaces resulting from the adhesion test have been investigated and the fracture behavior has been characterized. A difference in fracture mechanism between the three heat treatments has been found. The two cyclic heat treatments give fracture in the top coat/bond coat interface while isothermal heat treatment gives fracture in the top coat.

1234 1 - 50 of 172
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