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  • 1.
    Appelberg, Jesper
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Shibata, H.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    In situ studies of misch-metal particle behavior on a molten stainless steel surface2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 495, no 1-2, p. 330-334Article in journal (Refereed)
    Abstract [en]

    The use of misch-metal is widely spread among the stainless steel producers. Casting problems like clogging are common when using these additions. Information about Ce-La-Al-O particles formed due to the addition of misch-metal in the ladle is scarce in the open literature. The aim of this study is to increase the knowledge of the particle behavior and the particle characteristics in two stainless steels resulting from the addition of misch-metal. The in situ particle behavior has been studied using a Confocal Laser Scanning Microscope.

  • 2.
    Barkar, Thomas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Creep simulation of 9-12% Cr steels using the composite model with thermodynamically calculated input2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 395, no 1-2, p. 110-115Article in journal (Refereed)
    Abstract [en]

    Creep of 9-12% Cr steels is modeled using the composite model, developed by Blum et al. [R. Sedlacek, W. Blum, Comput. Mater. Sci. 25 (2002) 200], and thermodynamic calculations based on the Calphad approach. The composite model yields a physical description of the deformation behavior of materials that have a pronounced heterogeneous dislocation structure and is briefly surveyed. A few of the input parameters have been thermodynamically calculated using Thermo-Calc and introduced to the main program via a programming interface. This combined approach allows us to simulate the creep deformation behavior with less extensive microstructural investigations. This is a step towards enabling predictions of the creep behavior predominantly based on the nominal composition, heat treatment and mechanical load. Simulation results for two different 9-12% Cr steels are presented.

  • 3. Bergström, Lennart
    et al.
    Allibert, Colette
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Kostorz, Gernot
    International Symposium on Inorganic Interfacial Engineering 2006, Stockholm, Sweden, June 20–21, 20062008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 475, no 1-2, p. 1-Article in journal (Other academic)
  • 4.
    Chandrasekaran, Dilip
    et al.
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Nygårds, Mikael
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Comparison of surface displacement measurements in a ferritic steel using AFM and non-local plasticity2004In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 365, no 1-2, p. 191-195Article in journal (Refereed)
    Abstract [en]

    An attempt to experimentally study deformation characteristics around grain boundaries and to analyze the presence of strain gradients is presented. The evolution of surface profiles is studied by atomic force microscopy (AFM) at relatively small strains. The results indicate that this method can be used to draw conclusions about the deformation characteristics, e.g. in large grains the surface profile seems to vary within a grain. This latter effect can be seen as an indication of the inhomogeneous deformation occurring within large grains. The results are also compared with FEM calculations using a non-local crystal plasticity theory that incorporates strain gradients in the hardening moduli.

  • 5.
    Chen, Kaixuan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Science and Technology Beijing, China.
    Pan, Shiwei
    Zhu, Yuzhi
    Cheng, Yongjian
    Chen, Xiaohua
    Wang, Zidong
    In situ observations of crack propagation in as-cast Cu-1.5Fe-0.5Co (wt%) alloy2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 706, p. 211-216Article in journal (Refereed)
    Abstract [en]

    As-cast Cu-1.5Fe-0.5Co (wt%) alloy displays both high tensile strength of 307 MPa and elongation of 33%. In situ transmission electron microscopy was used to investigate crack propagation in the alloy, to analyze the origin of the good properties. At different deformation stages in thin Cu foils, the interactions of a propagating crack with iron-rich nanoparticles and growth twins are investigated. Crack-bridging processes via near-tip twinned bridges were identified. The multiple deformation mechanisms act synergistically to contribute to high strength and high ductility in the alloy.

  • 6. Dadbakhsh, S.
    et al.
    Vrancken, B.
    Kruth, J. P.
    Luyten, J.
    Van Humbeeck, J.
    Texture and anisotropy in selective laser melting of NiTi alloy2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 650, p. 225-232Article in journal (Refereed)
  • 7.
    Deirmina, Faraz
    et al.
    Siemens Energy AB, Finspang, Sweden..
    Koenig, Slawomir
    Siemens Energy AB, Finspang, Sweden..
    Hasselqvist, Magnus
    Siemens Energy AB, Finspang, Sweden..
    Oscarsson, Eva
    Siemens Energy AB, Finspang, Sweden..
    Adegoke, Olutayo
    Siemens Energy AB, Finspang, Sweden..
    Holländer Pettersson, Niklas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Pellizzari, Massimo
    Univ Trento, Dept Ind Engn, Via Sommar 9, I-38123 Trento, Italy..
    Influence of boron on the stress-rupture behavior of an additively manufactured Hastelloy X2023In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 863, article id 144483Article in journal (Refereed)
    Abstract [en]

    The influence of minor additions of boron and the as-built (AB) microstructure on stress-rupture behavior of a modified crack-free Hastelloy X fabricated by laser powder bed fusion (L-PBF) was investigated. Isothermal stress rupture tests were performed at 816 degrees C under a static tensile load of 103 MPa. Micro-void formation in the vicinity of carbide precipitates and their coalescence was only observed at chevron-like high-angle grain boundaries, characteristic of L-PBF process. These grain boundaries, laying on the planes with maximum resolved shear stress with respect to the loading direction, directly governed the intergranular crack propagation. In view of the fracture mechanism and the time to rupture, increasing boron content significantly improves timeto-rupture through a diffusion-controlled mechanism by hindering the carbon diffusion to the grain boundaries. Adequate additions of boron (>10 ppm) guarantee the stress-rupture properties (strength) of the AB components without the need for additional post-thermal treatments. Further increase in boron content (i.e., 30 ppm), led to about five times increase in time to rupture (500 h vs. 110 h), and significantly improved creep elongation (30% vs. 9%) compared with the low boron alloy.

  • 8. Dhindaw, B. K.
    et al.
    Kumar, L.
    Alkarkhi, N. C. Amer
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Microstructure development and solute redistribution in aluminium alloys under low and moderate shear rates during rheo processing2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 156-164Article in journal (Refereed)
    Abstract [en]

    Microstructural features and microsegregational behaviour of solute are studied in shear or stir-cast aluminium alloys under low and moderate shear rates. Alloys studied are Al-6.2% Cu, Al-7.3% Si and Al-13.2% Mg. In all the cases, microstructures of the primary pre-quench solid for stir-cast samples show rosette or ellipsoidal morphologies. Volume fractions of pre-quenched solid phase show significantly higher values for stir-cast alloys as compared to calculated. Microsegregation studies by microprobe analysis along the grains of the samples solidified under different treatment conditions show that stir casting changes the segregation pattern significantly. Except for Al-13.2% Mg alloys lower values than those calculated by Scheil's microsegregation equation are observed for other systems. A model for microstructure evolution during stir casting is presented. The microsegregation patterns have been discussed in terms of interaction between the diffusing solute and the vacancies migrating from solid into liquid.

  • 9.
    Ding, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. School of Material and Metallurgy, Inner Mongolia University of Science and Technology; Bayan Obo multimetallic resource comprehensive utilization Key lab, Inner Mongolia University of Science and Technology.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Yan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Bayan Obo multimetallic resource comprehensive utilization Key lab, Inner Mongolia University of Science and Technology.
    Heat treatment, microstructure and mechanical properties of a C-Mn-Al-P hot dip galvanizing TRIP steel2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, p. 151-157Article in journal (Refereed)
    Abstract [en]

    Heat treatments of a hot dip galvanizing TRIP (Transformation induced plasticity) steel with chemical composition 0.20C-1.50Mn-1.2Al-0.07P(mass%) were performed in a Gleeble 3500 laboratory equipment. The heat treatment process parameters were varied to investigate the effect of intercritical annealing temperature as well as isothermal bainitic transformation (IBT) temperature and time, on the microstructure and the mechanical properties. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy and x-ray diffraction, while mechanical properties were evaluated by tensile testing. Furthermore, to generate a better understanding of the phase transformations during heat treatment, dilatometry trials were conducted. The desired microstructure containing ferrite, bainite, retained austenite and martensite was obtained after the heat treatments. It was further found that the IBT is critical in determining the mechanical properties of the steel, since it controls the fraction of bainite. With increasing bainite fraction, the fraction of retained austenite increases while the fraction of martensite decreases. The mechanical properties of the steel are excellent with a tensile strength above 780 MPa (expect in one case) and elongation above 22%.

  • 10.
    Dong, Qian
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.
    Tang, Qing
    Li, Wenchao
    Al2O3-TiC-ZrO2 nanocomposites fabricated by combustion synthesis followed by hot pressing2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 475, no 1-2, p. 68-75Article in journal (Refereed)
    Abstract [en]

    Al2O3-TiC-ZrO2 nanocomposites were prepared by combustion synthesis followed by hot pressing with TiO2, Al, C and ZrO2 as raw materials. Combustion synthesis is favorable to obtain in situ formed powder with TiC and ZrO2 nanoparticles distributed in Al2O3 matrix. The effects of varying amount of ZrO2 nano-scale additives on the mechanical properties and microstructure of Al2O3-TiC composite were studied. An appropriate amount of ZrO2 nanoparticle additive improves the mechanical properties. The flexural strength and fracture toughness of Al2O3-TiC-10 wt.% ZrO2 composite were approximately 20% higher than that of Al2O3-TiC composite. The addition of ZrO2 nanoparticles reduced the grain size and improved the distribution of different phases. With the ZrO2 addition, the fracture mode changes from intergranular to mixed inter/transgranular fracture. The residual stresses are generated by the thermal expansion coefficient mismatch between different phases, which leads to the generation of dislocations and microcracks around the nanoparticles. The effects of nanoparticles on the deflected propagation, nailing and blocking of the dislocation and microcracks are believed to contribute to the improvement of the strength and toughness of Al2O3-TiC-ZrO2 composite.

  • 11. Egry, I.
    et al.
    Brillo, J.
    Matsushita, Taishi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Thermophysical properties of liquid Cu-Fe-Ni alloys2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 460-464Article in journal (Refereed)
    Abstract [en]

    Density and surface tension of liquid Cu-Fe-Ni alloys have been measured in an electromagnetic levitator over a wide temperature range, including the undercooled regime. Both properties are linear functions of temperature. Their concentration dependence, however, is highly nonlinear. The fit of the density data requires an excess volume containing a substantial ternary contribution. The surface tension is correctly predicted by the Butler equation from the thermodynamic potentials of the binary phases alone. In addition, a simple model is proposed which describes the surface tension reasonably well and requires as input the surface tensions of the pure components only.

  • 12.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    High-temperature mechanical- and fatigue properties of cast alloys intended for use in exhaust manifolds2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 616, p. 78-87Article in journal (Refereed)
    Abstract [en]

    In the present work materials for use in exhaust manifolds of heavy-duty diesel engines were tested in air from 20 to 1000 degrees C with respect to mechanical properties. Two cast irons, SiMo51 and Ni-resist D5S, four austenitic cast steels, HF, A3N, HK30 and HK-Nb, and one ferritic cast steel, 1.4509 were studied. The experimental work included thermal conductivity, thermal expansion, uniaxial stress-strain testing, low-cycle fatigue testing up to 30,000 cycles and fractography. Below 500 degrees C, SiMo51 is superior. At higher temperatures, a transition from elastic to plastic strain dominance was observed for the cast irons, reducing their performance. Carbide-forming elements increase heat conductivity and result in a dendrite-like fracture surfaces during fatigue testing. The austenitic steels are superior only at higher temperatures.

  • 13.
    Emi, Toshihiko
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    High-speed continuous casting of peritectic carbon steels2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 2-9Article in journal (Refereed)
    Abstract [en]

    Productivity of an integrated steel plant is improved by high-speed casting of hypo-peritectic steels that makes the productivity of caster meet basic oxygen furnace. In high-speed casting, however, strands of the steels tending to form cracks on the shell in the mold, require off-line conditioning that limits the plant productivity and premium yield. Hypo-peritectic transformation occurring on solidification in mold results in irregular shell-surface roughness that causes non-uniform heat transfer to the mold, causing local lifting of the shell from the mold, recalescence, and surface cracks. Influential factors are summarized on the development of the surface roughness, the non-uniform heat transfer and the decline of mechanical properties of the shell upon recalesce. Effective means are presented to reduce the non-uniformity and the cracks at high casting speeds by controlling the properties of mold flux film infiltrating into the solidifying shell/mold boundary.

  • 14. Eriksson, C. L.
    et al.
    Larsson, Per-Lennart
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Rowciffe, D. J.
    Strain-hardening and residual stress effects in plastic zones around indentations2003In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 340, no 02-jan, p. 193-203Article in journal (Refereed)
    Abstract [en]

    Plastic zones were revealed by polishing away Vickers indentations made in soda-lime glass, WC-11% Co, W and 7075 Al. Micro and nanohardness traces were used to explore the local mechanical response. The hardness value within the deformed zone increased up to 21% depending on the material. Soda-lime glass was the only material not to show a hardening effect, in fact it showed a small decrease in hardness. Finite element calculations were used to qualitatively determine the influence from residual stresses at indentation of soda-lime glass. The results are discussed in the context of the influence from work-hardening and residual stresses on indentation quantities.

  • 15.
    Fischer, Tim
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Gaisina, Vladilena
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Andersson, Michael
    organization=Höganäs AB, addressline=Bruksgatan 35, city=Höganäs, postcode=SE-263 83, country=Sweden, Bruksgatan 35.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Micromechanical prediction of the elastic and plastic properties of sintered steels2024In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 897, article id 146324Article in journal (Refereed)
    Abstract [en]

    One of the characteristic features of sintered steels is the porosity in their microstructure resulting from the compaction and sintering process. This porosity strongly influences the mechanical properties. To enhance the understanding for the structure–property relationship of sintered Astaloy®85Mo with 0.4 wt.%C, a micromechanical modelling approach based on face-centred cubic (fcc) representative volume elements (RVE) is proposed. The fcc-like periodic arrangement of the sintered particles in the RVE enables the consideration of a realistic non-spherical pore morphology. To compare the predictions with experimental results, accompanying uniaxial tensile tests are considered at different pore volume fractions after initial microstructure characterisation. In addition to the effect of pore volume fraction, the influence of sinter necks on the predicted overall strength is also systematically investigated. Despite the fairly simple nature of the underlying fcc structure, the RVE simulations are perfectly capable of reproducing the experimental trend, showing that the elasto-plastic properties decrease with increasing porosity. This is in contrast to analytical predictions, which underestimate the decrease in properties due to spherical pore assumptions. Moreover, the finite element-based simulations reveal a less pronounced influence of the sinter neck shape on the macroscopic behaviour, even though substantial differences in plastic strain localisation are discernible at the microscopic scale.

  • 16.
    Fischer, Tim
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Xiang, Shengmei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dahlberg, Carl F. O.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Creep-fatigue properties of austenitic cast iron D5S with tension and compression dwell: A dislocation density-based crystal plasticity study2022In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 860, p. 144212-, article id 144212Article in journal (Refereed)
    Abstract [en]

    To predict and better understand the creep-fatigue behaviour of austenitic cast iron D5S under tension and compression dwell at 800 degrees C, a physics-based crystal plasticity model that describes the complex rate-and temperature-dependent deformation of the material as a function of the dislocation density is implemented. In addition to the tension and compression dwell direction, the effect of three different dwell times (30, 180 and 600 s) on the creep-fatigue properties is investigated. The dislocation density-based crystal plasticity simulations are compared to experimental tests from a prior work. While relaxation tests and low-cycle fatigue (LCF) tests without dwell assist in systematically identifying the material parameters, creep-fatigue (CF) data is used to validate the predictions. The virtual testing is performed on a large-scale representation of the actual test specimen with a polycrystalline structure. To analyse the fatigue damage mechanism, small-scale predictions are also conducted using a micromechanical unit cell approach. Here, a single graphite nodule frequently found in the material is embedded into the austenitic matrix. In the present work, a close agreement is achieved between the predicted CF behaviour and the experimental results. Consistent with the experimental findings, the simulation results show that the addition of compression dwell leads to an uplift of the overall tensile stress level, which significantly reduces the fatigue life of the material. The unit cell studies demonstrate that during this uplift, a strong localisation of stresses and strains arises at the graphite/matrix interface, triggering the nucleation and growth of cavities and/or debonding.

  • 17.
    Fredriksson, Hasse
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, E.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A model of liquid metals and its relation to the solidification process2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 455-459Article in journal (Refereed)
    Abstract [en]

    X-ray analysis shows that a liquid is build up of clusters of atoms with a certain number of nearest neighbours. The X-ray analysis shows that 8-11 nearest neighbours surround each atom. Each cluster has a crystal-like structure. Between the clusters there are some free atoms and free electrons. The enthalpy of fusion is according to Richard's rule around the gas constant times the temperature of melting and the heat capacity in the liquid state is normally constant and for some metals lower than that in the solid state. For metals with low melting points it will decrease further with increasing temperature. This behaviour of the metals can be explained by the use of statistical mechanics and by assuming that the clusters, observed by X-ray analysis are rotating around a centre of its mass. The cluster model is applied to explain the diffusion rate in liquid metals. The effect of the experimental set upon measurements of diffusion constants is discussed as well as its effect on crystal growth.

  • 18.
    Fredriksson, Hasse
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Stjerndahl, J.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Tinoco, J.
    On the solidification of nodular cast iron and its relation to the expansion and contraction2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 363-372Article in journal (Refereed)
    Abstract [en]

    Directional solidification and quench-out thermal analysis experiments have been performed in Mg-treated cast iron alloys. The volume fraction of liquid, allstenite and graphite was evaluated. It was observed that the volume fraction of austenite is much larger than expected from the equilibrium phase diagram at the beginning of the solidification process. It was also been observed that the last melt solidifies far below the equilibrium eutectic temperature. The solidification process was analyzed by non-equilibrium thermodynamic models. The theoretical treatment was supported by the observation that the latent heat decreases during the solidification process. The formation of small pores was observed at the very end of the solidification. An explanation for the formation of the small pores is given in terms of a vacancies creep model. The formation of macropores was related to the large fraction of austenite formed during the first part of the solidification process.

  • 19.
    Fredriksson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Size-dependent yield strength and surface energies of thin films2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 400-401, no 1-2 SUPPL., p. 448-450Article in journal (Refereed)
    Abstract [en]

    The strain gradient plasticity theory recently proposed by Gudmundson [P. Gudmundson, J. Mech. Phys. Solids 52 (2004) 1379-1406] is used to analyse the behaviour of a thin film on an elastic substrate. Boundary conditions for the film-substrate interface are introduced via a surface energy that depends on the plastic strain state at the interface. Finite element results show a strong dependence on the surface energy. If the surface energy is small, no size effects appear. On the other hand, if a stiff interface is simulated, corresponding to a large surface energy, a thickness dependence of the yield strength is found. The application of several alternative strain gradient models would predict a thickness dependent hardening, but strictly not a size dependence of the yield strength. The presently predicted thickness dependence on yield strength and hardening is supported by experimental results.

  • 20.
    Gaisina, Vladilena
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Andersson, Michael
    Höganäs AB, Höganäs, Sweden.
    Bonvalet Rolland, Manon
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    On the mechanical behavior of sintered Astaloy-85Mo: Influence of porosity and sinter conditions2022In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 841, p. 143052-143052, article id 143052Article in journal (Refereed)
    Abstract [en]

    Astaloy™ 85 Mo is a pre-alloyed, water-atomized 0.85% Mo steel powder. The aim of the present investigation is to study the influence of porosity, controlled by both mechanical and thermal processing, on the mechanical properties in a bainitic microstructure of a pressed and sintered steel. To achieve this, uniaxial tensile and compression testing is performed, together with Vickers macro- and microhardness experiments. Microhardness testing is carried out in order to determine the behavior of the matrix material at a scale where porosity influence is minimized. Both the influence from size and shape of the pores is investigated and compared with relevant mechanical analyses for porous solids. Such mechanical analyses are pertinent to both elastic and plastic properties, where in the latter case the well-known Gurson-Tvergaard model for solids with spherical pores is relied upon. It is shown that assuming a spherical pore shape is not sufficient in order to achieve good agreement between predictions and experimental results and will be further investigated in future studies.

  • 21.
    Ganchenkova, Marija G
    et al.
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Borodin, V A
    Monte-Carlo simulation of crack propagation in polycrystalline materials2004In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 387, p. 372-376Article in journal (Refereed)
    Abstract [en]

    The paper deals with a model for transgranular crack propagation in a polycrystalline metals and alloys. According to experimental observations, the fracture surfaces (facets) remain perfectly flat within each individual grain, but the orientation of facets fluctuates from grain to grain. At the bigger length scales, this behaviour results in the roughness of fracture surface. The polycrystalline structure of simulated material is represented by pseudo-3D grain array. The "grain by grain" mode of crack propagation is simulated in terms of a "continuous time" kinetic Monte-Carlo (MC). The stochastic nature of the proposed model allows to estimate energy consumption during fracture and fracture surface topography, and provides a natural explanation for the experimentally observed scatter of macroscopic fracture characteristics.

  • 22.
    Ge, Shaofan
    et al.
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;Univ Sci & Technol China, Sch Mat Sci & Engn, Hefei 230026, Peoples R China..
    Fu, Huameng
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;Dongguan Eontec Co Ltd, Dongguan 523662, Guangdong, Peoples R China..
    Zhang, Long
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China..
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics. Thermocalc Software AB, Rasundavagen 18A, SE-16967 Solna, Sweden..
    Li, Hong
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;Dongguan Eontec Co Ltd, Dongguan 523662, Guangdong, Peoples R China..
    Wang, Aimin
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;Dongguan Eontec Co Ltd, Dongguan 523662, Guangdong, Peoples R China..
    Li, Weirong
    Dongguan Eontec Co Ltd, Dongguan 523662, Guangdong, Peoples R China..
    Zhang, Haifeng
    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;Dongguan Eontec Co Ltd, Dongguan 523662, Guangdong, Peoples R China..
    Effects of Al addition on the microstructures and properties of MoNbTaTiV refractory high entropy alloy2020In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 784, article id 139275Article in journal (Refereed)
    Abstract [en]

    AlxMoNbTaTiV alloys are designed according to the binary phase diagrams and calculation of phase diagrams (CALPHAD). The phase formation and elemental segregation are predicted using the CALPHAD method. The effects of Al on microstructures, and mechnical properties of AlxMoNbTaTiV are investigated, which verified the results of calculated dendritic microstructure and BCC structure. The strengthening mechanism is proved as the result of chemical and electrical interactions. The serration behavior in the compression test at 25 degrees C, 500 degrees C, 700 degrees C, 900 degrees C is discussed. At room temperature, addition of Al enhanced the dynamic aging effects in low concentration. The effects became weaker with the increase of Al content. At 500 degrees C, higher Al concentration leads to stronger serrated flow.

  • 23.
    He, Junjing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Creep cavity growth models for austenitic stainless steels2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, p. 328-334Article in journal (Refereed)
    Abstract [en]

    Diffusion controlled cavity growth models tend to exaggerate the growth rate. For this reason it is essential to take into account the restrictions caused by creep rate of the surrounding material, so called constrained growth. This has the consequence that the stress that the cavities are exposed to is reduced in comparison to the applied creep stress. Previous constrained growth models have been based on linear viscoplasticity. To avoid this limitation a new model for constrained growth has been formulated. Part of the work is based on a FEM study of expanding cavities in a creeping material. Compared with the previous constrained cavity growth models, the modified one gives lower reduced stresses and thereby lower cavity growth rates. By using recently developed cavity nucleation models, the modified creep cavity growth model can predict the cavity growth behaviour quantitatively for different types of austenitic stainless steels, such as 18Cr10Ni, 17Cr12NiNb and 17Cr12NiTi.

  • 24.
    Hedström, Peter
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Baghsheikhi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Liu, Ping
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    A phase-field and electron microscopy study of phase separation in Fe-Cr2012In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 534, p. 552-556Article in journal (Refereed)
    Abstract [en]

    Phase separation in the binary Fe-Cr system, the basis for the entire stainless steel family, is considered responsible for the low temperature embrittlement in ferritic, martensitic and duplex stainless steels. These steels are often used in load-bearing applications with considerable service time at elevated temperature. Thus, understanding the effect of microstructure on mechanical properties and predicting dynamics of phase separation are key issues. In the present work, experimental evaluation of structure and mechanical properties in binary Fe-Cr alloys as well as phase-field modeling, using a new thermodynamic description of Fe-Cr, is conducted. A significant hardening evolution with time is found for alloys aged between 400 and 550 degrees C, and it can be attributed to phase separation. The decomposed structure changed with increasing Cr content at 500 degrees C. with a more particle-like structure at 25 wt% Cr and a more spinodal-like structure at 30 wt% Cr. The observed transition of structure agrees with the thermodynamically predicted spinodal, although the transition is expected to be gradual. The phase-field simulations qualitatively agree with experiments. However, to enable accurate quantitative predictions, the diffusional mobilities must be evaluated further and thermal fluctuations as well as 3D diffusion fields must be properly accounted for.

  • 25.
    Hedström, Peter
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Huyan, Fei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Zhou, Jing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Wessman, Sten
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, Mattias
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    The 475 degrees C embrittlement in Fe-20Cr and Fe-20Cr-X (X=Ni, Cu, Mn) alloys studied by mechanical testing and atom probe tomography2013In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 574, p. 123-129Article in journal (Refereed)
    Abstract [en]

    In the present work the 475 degrees C embrittlement in binary Fe-Cr and ternary Fe-Cr-X (X=Ni, Cu and Mn) alloys have been investigated. The mechanical properties were evaluated using microhardness and impact testing, and the structural evolution was evaluated using atom probe tomography (APT). The APT results after aging at 500 degrees C for 10 h clearly showed that both Ni and Mn accelerate the ferrite decomposition. No evident phase separation of either the Fe-20Cr or Fe-20Cr-1.5Cu samples was detected after 10 h of aging and thus no conclusions on the effect of Cu can be drawn. Cu clustering was however found in the Fe-20Cr-1.5Cu sample after 10 h aging at 500 degrees C. The mechanical property evolution was consistent with the structural evolution found from APT. Samples aged at 450 and 500 degrees C all showed increasing hardness and decreasing impact energy. The embrittlement was observed to take place mainly during the first 10 h of aging and it could primarily be attributed to phase separation, but also substitutional solute clustering and possibly carbon and nitrogen segregation may contribute in a negative way.

  • 26.
    Heshmati, Nader
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Sieurin, Henrik
    Scania CV AB, Materials Technology,Södertälje, SE-151 87, Sweden.
    Larsson, Joachim
    SSAB,Borlänge, SE-781 84, Sweden.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Correlation between microstructure and fatigue properties of hot-rolled thick-plate complex-phase steel2023In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 885, article id 145624Article in journal (Refereed)
    Abstract [en]

    Complex-phase (CP) steels, with a multiphase microstructure, offer an excellent combination of high strength, ductility, and formability, making them an attractive alternative to conventional high-strength low-alloy (HSLA) steels in the automotive industry. However, the microstructure and fatigue property relation in CP steels is complex. This limits the full exploitation of CP steels in applications, such as heavy-vehicles, where excellent fatigue performance of thick-plates after punching holes is the critical parameter. In this work, we initiate the study of the relation between microstructure and fatigue properties of a commercial CP steel (800CP) and compare it with a conventional HSLA (500MC) steel. Fatigue property, tensile property, and fatigue crack growth rate (FCGR) testing are conducted and the performance of the two steels is rationalized using detailed microstructure characterization, before and after fatigue testing. FCGR testing shows that, despite a higher yield strength of the 800CP, both steels have a similar propagation rate due to a more tortuous crack propagation path and a higher quantity of secondary crack formation in the 800CP microstructure. The high cycle fatigue (HCF) testing shows that the fatigue limit in the 800CP is 25% higher. This increase in fatigue limit is attributed to the improved resistance to fatigue crack initiation in the 800CP due to its larger fraction of bainite.

  • 27.
    Hoseini-Athar, M. M.
    et al.
    Univ Tehran, Coll Engn, Sch Met & Mat Engn, Tehran, Iran..
    Mahmudi, R.
    Univ Tehran, Coll Engn, Sch Met & Mat Engn, Tehran, Iran..
    Babu, Prasath
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Microstructural evolution and superplastic behavior of a fine-grained Mg-Gd alloy processed by constrained groove pressing2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 754, p. 390-399Article in journal (Refereed)
    Abstract [en]

    In the current study, microstructural evolution and superplasticity of an extruded Mg-2wt% Gd sheet were studied after the constrained groove pressing (CGP) process. Microstructural observations by scanning electron microscopy and electron backscattered diffraction revealed that after 4 cycles of CGP, a rather homogeneous fine-grained microstructure with an average grain size of 4.3 mu m, and a large fraction of high angle grain boundaries was obtained. By performing shear punch tests (SPT) at different temperatures and various shear strain rates, a peak strain rate sensitivity index (m-value) of 0.49 was obtained after 4 cycles of CGP process at 673 K, while peak m-values of 0.31 and 0.36 were obtained for the as-extruded and 2 cycle CGP process conditions, respectively. An m-value of 0.49 and an activation energy of 113 kJ/mol, obtained for the fine-grained material after 4 cycles of CGP, suggest that the dominant deformation mechanism in the superplastic regime is grain boundary sliding (GBS) controlled by grain boundary diffusion.

  • 28.
    Hoseini-Athar, M. M.
    et al.
    Univ Tehran, Coll Engn, Sch Met & Mat Engn, Tehran, Iran..
    Mahmudi, R.
    Univ Tehran, Coll Engn, Sch Met & Mat Engn, Tehran, Iran..
    Babu, Prasath
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Microstructure, texture, and strain-hardening behavior of extruded Mg-Gd-Zn alloys2020In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 772, article id 138833Article in journal (Refereed)
    Abstract [en]

    The effect of Zn content on the microstructure, texture, mechanical properties and strain-hardening behavior of extruded Mg-2Gd-xZn (x = 0, 1, 2 and 3 wt%) sheets was investigated. Evaluation of texture revealed that while all of the alloys exhibited weak textures, the texture component was altered from a basal to a non-basal one by the addition of Zn. A typical transverse direction (TD) split texture with basal poles rotated about 40 degrees from the normal direction (ND) toward TD was observed for the Zn-containing alloys, the effect being more pronounced at higher Zn contents. Furthermore, the Mg-2Gd-1Zn alloy exhibited the weakest texture due to solute drag imposed by co-segregation of Zn and Gd atoms at grain boundaries. Addition of Zn also resulted in a general increase in yield stress, ultimate tensile strength and elongation along the extrusion direction from 99 to 172 MPa, 178 to 263 MPa, and 25 to 35% for Mg-2Gd and Mg-2Gd-3Zn alloys, respectively. However, increasing Zn content was accompanied by an initial decrease in anisotropy of mechanical properties and strain-hardening behavior, followed by an increase at higher Zn contents. This was due to the difference of orientation of basal planes with regard to tension direction. As a result, lower yield stress, higher elongation and strain-hardening capacity was obtained along TD (with higher Schmid factor for basal slip) compared to ED. It was concluded that excellent mechanical properties and low anisotropy can be achieved in the Mg-2Gd-1Zn alloy.

  • 29.
    Hoseini-Athar, Mohammad Mehdi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Univ Tehran, Sch Met & Mat Engn, Coll Engn, Tehran, Iran.
    Mahmudi, R.
    Univ Tehran, Sch Met & Mat Engn, Coll Engn, Tehran, Iran..
    Revathy Rajan, Prasath Babu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Microstructure and superplasticity of Mg-2Gd-xZn alloys processed by equal channel angular pressing2021In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 808, article id 140921Article in journal (Refereed)
    Abstract [en]

    Microstructure, mechanical properties and superplastic behavior of Mg-2Gd-xZn (x = 0, 1, 2 and 3 wt%) alloys were investigated after extrusion and equal channel angular pressing (ECAP). After only 2 passes of ECAP, a homogenous fine-grained microstructure with a grain size of 2.33 mu m and a high fraction of high-angle grain boundaries of 84% were formed in the Mg-2Gd-3Zn (GZ23) alloy, while 4 ECAP passes were necessary to create such a structure in the other alloys. This was attributed to the higher solute drag effect in the other alloys, retarding dynamic recrystallization (DRX). Although DRX occurred more easily in the GZ23 alloy, the final DRX grain size was slightly coarser compared to the other alloys. Shear punch testing (SPT) showed that grain refinement during ECAP leads to a slight increase in the shear yield strength of all studied materials after 2 ECAP passes, which was mostly balanced by texture softening caused by the shear texture component and grain growth after 4 ECAP passes. Contrary to the other alloys, the GZ23 alloy exhibited superplastic behavior after a lower number of ECAP passes. In addition, the superplastic temperature for GZ23 was 648 K, which was lower than the 673 K observed for the other alloys. The m-values of similar to 0.45-0.5 and activation energies of 98-114 kJ/mol suggested grain boundary sliding (GBS) controlled by grain boundary diffusion as the dominant deformation mechanism in the superplastic regime. This was confirmed by microstructural observations.

  • 30.
    Huitron, Rosa M. Pineda
    et al.
    Lulea Univ Technol, Mat Sci, Dept Engn Sci & Math, SE-97187 Lulea, Sweden..
    Lopez, Pavel E. Ramirez
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. SWERIM AB, Casting & Flow Simulat Grp, Proc Met Dept, Aronstorpsvagen 1, SE-97437 Lulea, Sweden..
    Vuorinen, Esa
    Lulea Univ Technol, Mat Sci, Dept Engn Sci & Math, SE-97187 Lulea, Sweden..
    Jentner, Robin
    Lulea Univ Technol, Mat Sci, Dept Engn Sci & Math, SE-97187 Lulea, Sweden..
    Karkkainen, Maija E.
    SSAB Europe Oy Raahe Works, Rautaruukintie 155,PL 93, Raahe 92101, Finland..
    Converging criteria to characterize crack susceptibility in a micro-alloyed steel during continuous casting2020In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 772, article id 138691Article in journal (Refereed)
    Abstract [en]

    The ductility drop and decrease in strength that lead to crack formation during continuous casting of steel is typically investigated by means of the hot ductility test. In this study, hot ductility tests are performed by using a thereto-mechanical Gleeble system to simulate the deformation of steels at high temperatures and low deformation rates similar to those during continuous casting. Thus, temperature was varied between 600 and 1000 degrees C while strain rates covered a range from 0.001 to 0.1 s(-1). Tests are carried out to identify the temperature range at which the steel is susceptible to crack formation as well as the effect of strain rate. Characterization of fractured surfaces and phase transformation after thermo-mechanical tests are conducted in the SEM and Optical Microscope. The combination of these techniques makes possible to formulate cracking mechanisms during hot processing which show critical strain for failure at temperatures between 700 and 900 degrees C based on the convergence of three different criteria: I) Reduction of area, II) True fracture strength-ductility and III) True total energy. This approach provides a better understanding of crack formation in steels at the high temperatures experienced during continuous casting. This information is key to productivity losses and avoid defect formation in the final cast products.

  • 31. Hulme-Smith, Christopher
    et al.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Erratum to "Mechanical properties of thermally-stable, nanocrystalline bainitic steels" [Materials Science & Engineering A 700 (2017) 714-720]2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 704, no AugustArticle in journal (Other academic)
  • 32.
    Hulme-Smith, Christopher
    et al.
    University Of Cambridge.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Mechanical properties of thermally-stable, nanocrystalline bainitic steels2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 700, p. 714-720Article in journal (Refereed)
    Abstract [en]

    Two novel, thermally stable bulk nanocrystalline bainitic steels were subjected to a range of mechanical tests. One alloy, containing 0.72 wt% carbon exhibited an ambient-temperature 0.2% proof strength of 1500 MPa and a fracture toughness of 64.6 MPa m<sup>1/2</sup> after the bainite transformation. The other, containing 0.45 wt% carbon and 13.2 wt% nickel, had a 0.2% proof stress of 1000 MPa and a fracture toughness of 103.8 MPa m<sup>1/2</sup> . Both steels showed excellent creep resistance, with a rupture life at 450 ˚C and 700 MPa of 114 h and 94.8 h, respectively. Both displayed fatigue lives consistent with other steels of similar structure in the literature. After thermal exposure at 480 ˚C for 8 d, both steels increased in strength to 1800 MPa, and 1600 MPa, respectively. The latter steel reduced in fracture toughness to 19.6 MPa m<sup>1/2</sup> . These alloys are suitable for a range of engineering applications and remain so after thermal exposure. Combined with impressive high-temperature performance, this

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  • 33. Hättestrand, Mats
    et al.
    Larsson, Petter
    Chai, Guocai
    Nilsson, Jan-Olof
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Study of decomposition of ferrite in a duplex stainless steel cold worked and aged at 450-500°C2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 499, p. 489-492Article in journal (Refereed)
    Abstract [en]

    The influence of cold-deformation on ferrite decomposition in duplex stainless steel during heat treatment at 450-500 °C was investigated using micro-hardness measurements and transmission electron microscopy. It was found that cold-deformation can change the mechanism of the α → α + α′ phase separation in the ferrite from nucleation and growth to spinodal decomposition. This finding is discussed in terms of the influence of an increased dislocation density on coherency strains

  • 34.
    Iyer, Anand H.S.
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Gupta, Priyank
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Measuring microscale mechanical properties of PVdF binder phase and the binder-particle interface using micromechanical testing2023In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 881, article id 145352Article in journal (Refereed)
    Abstract [en]

    In this study, we developed a robust methodology for extracting the mechanical properties of individual components in complex systems such as Li-ion battery electrodes and provided quantitative values that can be used as input for modelling and lifetime estimation of Li-ion batteries. We employed micromechanical testing techniques, including micropillar compression, microcantilever bending, and nanoindentation, to measure the mechanical properties of the PVdF binder phase in the active layer. We discovered that nanoindentation tends to overestimate the modulus due to uncertainty associated with the test volume and initial large compression strains, while the micropillar compression technique provides more accurate modulus data with a narrower spread. Additionally, the yield stress of the binder phase can be evaluated using micropillar compression. Our obtained modulus values were in the range of 2.5–4.4 GPa, and the yield stress was in the range of 162–270 MPa. By microcantilever bending tests, we determined that the binder–particle interface often fails before the binder itself, suggesting that the interface significantly influences the failure mechanics. Overall, our results indicate that the microcantilever bending tests provide moduli estimates that agree with those obtained from micropillar compression tests. We also qualitatively examined the binder-particle and binder-current collector interfaces, further emphasising the significance of our methodology and the obtained quantitative values.

  • 35.
    Kese, Kwadwo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Li, Zhi-Cheng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Method to account for true contact area in soda-lime glass during nanoindentation with the Berkovich tip2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 404, no 1-2, p. 1-8Article in journal (Refereed)
    Abstract [en]

    An. empirical relationship for estimating the pile-up contact area from the contact stiffness, S and the contact depth, h(c) has been developed. This was achieved first by using the atomic force microscope to image nanoindents made with the Berkovich indenter in soda-lime glass and approximating the pile-up contact perimeter as a semi-ellipse. Then, by determining the pile-up contact area for several peak indentation loads, a correlation was found between the pile-up contact area and the load used to generate it. The importance of this new method of determining the pile-up contact area is that the need for indent imaging is made completely redundant, since the contact stiffness is a quantity that is routinely obtained during nanoindentation data analysis. Elastic modulus of soda-lime glass of 70 +/- 1.5 GPa is measured with loads ranging from 20 to 500 mN. The hardness measured also falls within the range of values, 5.2-5.9 GPa, normally quoted in the literature for the glass.

  • 36.
    Kivisäkk, Ulf
    Sandvik Materials Technology.
    Investigation of low-temperature creep and microhardness of asuperduplex stainless steel and the relationship of these properties to themicrostructure and the mechanism for HISCIn: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936Article in journal (Other academic)
  • 37.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    First-principles evaluation of the effect of alloying elements on the lattice parameter of a 23Cr25NiWCuCo austenitic stainless steel to model solid solution hardening contribution to the creep strength2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 626, p. 213-219Article in journal (Refereed)
    Abstract [en]

    By the use of first-principles calculations based on density functional theory, lattice misfit parameters for alloying elements in the austenitic stainless steel 23Cr25NiWCuCo have been derived. These lattice misfit parameters have been applied to determine the solid solution hardening of the elements W, Nb, and Cu in the steel. The model for solid solution hardening is based on work by Hirth and Lothe, where solutes are creating Cottrell clouds around the dislocations and slow down their motion. The model is also verified by comparison to creep tests for Ni-20%Cr and Ni-20%Cr-6W, where W is almost completely in solid solution and no other strengthening mechanism than solid solution hardening should be active. The contribution from the interstitial elements C and N to the solid solution hardening is found to be negligibly small for the studied steel.

  • 38.
    Lagerstedt, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A model for prediction of cracks in a solidifying shell2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 37-43Article in journal (Refereed)
    Abstract [en]

    A model coupling temperature and stress calculations with cracking criteria has been developed in order to predict crack positions in a solidifying shell. The model is based on a one-dimensional FDM approach suitable for continuous casting of slabs. The strain/stress model is based on a purely elastic analysis of a solidifying shell giving a straightforward comparison between stresses and crack criteria. This approach makes the model easy to use. The model is numerically evaluated using available material data for Fe-2%Ni with primary ferrite solidification and Fe-10%Ni with primary austenitic solidification. The results of the calculations are discussed and the impact of material behavior as well as process parameters is evaluated. Evaluation of the influence of changes in the heat transfer coefficient shows that the rapid changes introduce stresses large enough to induce crack formation in the solidifying shell.

  • 39.
    Lagerstedt, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Kron, Jenny
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Hailom Yosef, Futsum
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Measurements and modeling of air gap formation in iron-base alloys2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 44-51Article in journal (Refereed)
    Abstract [en]

    The formation of an air gap has been experimentally studied during solidification of several iron-based alloys. Air gap widths and temperature distribution have been measured during solidification in a cylindrical water-cooled Cu-mold. Mathematical modeling has been performed to increase the understanding of the solidification process and the air gap formation. A model, developed earlier for Al- and Cu-based alloys, for description of air gap formation in alloys solidifying with varying solidification intervals was tested for Fe-base alloys. The model includes the effect of formation and condensation of lattice defects on the solidification process and the air gap formation. The calculated shrinkage using this model shows good agreement with the experimental data.

  • 40. Li, Dong-gang
    et al.
    Wang, Qiang
    Li, Guo-jian
    Lv, Xiao
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    He, Ji-cheng
    Diffusion layer growth at Zn/Cu interface under uniform and gradient high magnetic fields2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 495, no 1-2, p. 244-248Article in journal (Refereed)
    Abstract [en]

    As a common phenomenon occurring in many material processes, diffusion may induce significant changes in composition and microstructure near the interface. In the present study, liquid/solid (Zn/Cu) interface diffusion experiments in high magnetic fields (up to 12 T) were conducted and the thickness changes of diffusion layer under different magnetic field conditions were examined. It was found that there were no noticeable effects of high magnetic fields on the formation of intermetallic phases at the interface. However, the magnetic flux density exerted a non-linear influence on the diffusion layer thickness. This phenomenon should be attributed to the effect of magnetic fields suppressing natural convection and inducing thermo-electromagnetic convection. In addition, the diffusion of Zn into Cu could be retarded by a magnetic field gradient. These results indicate that both the strength and the gradient of high magnetic fields can be used to control the diffusion behavior.

  • 41.
    Li, Pei
    et al.
    Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Shaanxi, Peoples R China..
    Zhang, Tianlong
    Xi An Jiao Tong Univ, Frontier Inst Sci & Technol, Ctr Microstruct Sci, Xian 710049, Shaanxi, Peoples R China..
    Sun, Xun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Xi An Jiao Tong Univ, Frontier Inst Sci & Technol, Ctr Microstruct Sci, Xian 710049, Shaanxi, Peoples R China.
    Zhang, Hualei
    Xi An Jiao Tong Univ, Frontier Inst Sci & Technol, Ctr Microstruct Sci, Xian 710049, Shaanxi, Peoples R China..
    Wang, Dong
    Xi An Jiao Tong Univ, Frontier Inst Sci & Technol, Ctr Microstruct Sci, Xian 710049, Shaanxi, Peoples R China..
    Sun, Qiaoyan
    Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Shaanxi, Peoples R China..
    Xiao, Lin
    Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Shaanxi, Peoples R China..
    Sun, Jun
    Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Shaanxi, Peoples R China..
    Secondary hardening behavior in Ti alloy2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, p. 640-647Article in journal (Refereed)
    Abstract [en]

    We report the existence of secondary hardening behavior in Ti-10V-2Fe-3Al (wt.%) (Ti-1023) for the first time. Through controlling the ageing temperature window between 550 degrees C and 575 degrees C, alloys are found to show the existence of two hardness peaks with aging time. This heat treatment with secondary hardening phenomenon exhibits unusual increase of hardness and strength. Further experimental observations show that the first hardness peak corresponds with the well precipitated alpha phase at very short time. Further increase of aging time does not influence the morphology of these intragranular alpha precipitates, but accompanying with a continuous composition change, which could be the origin of the secondary hardness peak. This structure change followed by composition diffusion is the typical characteristic of pseudospinodal mechanism. Phase field and ab-initio calculations based on pseudospinodal mechanism analyze the detailed microstructure/composition evolution and related solid solution strength, which confirm the role of composition on the appearance of secondary hardening behavior.

  • 42.
    Li, Wang
    et al.
    Univ Sci & Technol, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Deng, Yue
    Univ Sci & Technol, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Gu, Jinbo
    Univ Sci & Technol, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Mu, Wangzhong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Li, Jingyuan
    Univ Sci & Technol, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Correlation of microstructure and dynamic softening mechanism of UNS S32101 duplex stainless steel during elevated temperature tensile testing2022In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 855, article id 143868Article in journal (Refereed)
    Abstract [en]

    The dynamic substructural development and softening mechanism of UNS S32101 duplex stainless steel were comprehensively investigated by employing hot-tensile tests at various strain rates of 0.1-10 s(-1) at a fixed temperature of 1200 degrees C. Different flow behaviors were attributed to the microstructural evolution and restoration process under various hot-deformation conditions. The alternative restoration mechanisms of ferrite in the current alloy were closely associated with the evolution of the misorientation angle in the (sub)grains, depending on the applied strain rates. Therein, three distinct softening mechanisms were found in ferrite, i) subgrain coalescence (SC) at 0.1 s(-1), ii) continuous dynamic recrystallization (CDRX) at 1 s(-1) and iii) subgrain rotationassisted discontinuous dynamic recrystallization (SR-assisted DDRX) at 10 s(-1). During SR-assisted DDRX process, new DRX nuclei were preferentially formed at the high-angle grain boundaries/phase boundaries (HAGBs/PBs) through the growth of highly misoriented subgrains. In contrast to ferrite, the available dynamic softening behavior of austenite, unlike the classical DDRX mechanism characterized by strain-induced boundary migration (SIBM), is affected by a limited number of pre-existing HAGBs. At lower strain rates of 0.1 and 1 s(-1), the nucleation process of DRX in austenite is analogous to the CDRX behavior, whereas the growth characteristics conform to DDRX, thus, it can be called dynamic recovery-assisted DDRX (DRV-assisted DDRX). At a high strain rate of 10 s(-1), DRX nucleation mainly took place through the strain-induced twin boundaries (TBs) transformation into HAGBs, and then rapidly grew via SIBM, referred to as TB-assisted DDRX.

  • 43.
    Li, Wang
    et al.
    Univ Sci & Technol Beijing, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Gu, Jinbo
    Univ Sci & Technol Beijing, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Deng, Yue
    Univ Sci & Technol Beijing, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Mu, Wangzhong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Jingyuan
    Univ Sci & Technol Beijing, Beijing Adv Innovat Ctr Mat Genome Engn, Sch Mat Sci & Engn, Beijing 100083, Peoples R China.;Univ Sci & Technol, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    New comprehension on the microstructure, texture and deformation behaviors of UNS S32101 duplex stainless steel fabricated by direct cold rolling process2022In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 845, p. 143150-, article id 143150Article in journal (Refereed)
    Abstract [en]

    The effect of cold deformation on the detailed microstructure evolution, texture development and deformation behaviors/mechanisms of UNS S32101 duplex stainless steel (DSS2101) during the direct cold rolling process was investigated. The results showed that throughout the cold deformation process, the negative texture of {001}<110> component was nonexistent in deformed ferrite, and most texture components were mainly concentrated on alpha/gamma-fibers. Detwinning in austenite was substantial responsible for the reorientation in {111}< 112> towards {111}<110> of gamma-fiber in ferrite rather than martensite transformation. Austenite texture were composed of {110}<100> Goss and {110}<115> Goss/Brass components at heavy deformation (50% and 70%). The refinement and deformation behavior in ferrite was attributed to microbands (MBs) subdivision and dislocation activities, whilst that of austenite mainly occurred through twinning, strain induced detwinning (SID) and strain induced martensite (SIM).

  • 44.
    Li, Wang
    et al.
    Beijing Advanced Innovation Center for Materials Genome Engineering, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; School of Materials Science and Engineering, University of Science and Technology Beijing 100083, P. R. China.
    Li, Jingyuan
    Beijing Advanced Innovation Center for Materials Genome Engineering, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; School of Materials Science and Engineering, University of Science and Technology Beijing 100083, P. R. China.
    Gong, Qingdi
    Beijing Advanced Innovation Center for Materials Genome Engineering, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; School of Materials Science and Engineering, University of Science and Technology Beijing 100083, P. R. China.
    Guo, Huihua
    Beijing Advanced Innovation Center for Materials Genome Engineering, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; School of Materials Science and Engineering, University of Science and Technology Beijing 100083, P. R. China.
    Cao, Zhu
    Beijing Advanced Innovation Center for Materials Genome Engineering, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; School of Materials Science and Engineering, University of Science and Technology Beijing 100083, P. R. China.
    Mu, Wangzhong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Annealing parameters effect on microstructure evolution, tensile properties and deformation behaviors of direct-cold-rolled UNS S32101 duplex stainless steel with heterogeneous layered structure2023In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 883, article id 145439Article in journal (Refereed)
    Abstract [en]

    Microstructure evolution, strain-induced martensite transformation (SIMT) kinetics, tensile properties, deformation behaviors of UNS S32101 duplex stainless steel (DSS) with heterogeneous layered structure (HLS) were investigated. HLS composed of multiscale grains (spanning coarse, fine, and ultrafine grains) was prepared by direct cold rolling in combination with short-time annealing, being dominated by coarse-grained ferrite (CGed α) and fine-grained austenite (FGed γ). A quantitative SIMT kinetics model was established to predict the α′-martensite fraction at various strain/annealing parameters, indicating that increased average grain size (AGS) for γ not only contributed to the SIM formation but also promoted the monotonic increase of SIMT rate until annealing for 10 min. Relatively high stacking fault energy (SFE, 35.89∼39.34 mJ/m2) favored mechanical twinning as the dominant deformation mode of γ accompanied by SIMT and dislocation glide. And α deformation was mainly coordinated by wavy slip. Both SFE and Olson-Cohen parameters were strongly correlated with the γ AGS, which could reasonably interpret the dependence of SIMT on the AGS. The A and B values increased progressively with grain coarsening along with the rapid decline in SFE, facilitating the martensite formation. Further increasing the AGS beyond the peak region severely suppressed SIMT probably due to the low probability of martensite embryo generation at deformation twins (DTs) intersections, coinciding with the sharp decrease A value.

  • 45. Li, Wenjiang
    et al.
    Fu, Tao
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Preparation of free-standing silica 3D colloidal crystal film at water-air interface2006In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 441, no 01-2, p. 239-244Article in journal (Refereed)
  • 46.
    Magnusson, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. KTH, School of Industrial Engineering and Management (ITM), Centres, Brinell Centre - Inorganic Interfacial Engineering, BRIIE.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. KTH, School of Industrial Engineering and Management (ITM), Centres, Brinell Centre - Inorganic Interfacial Engineering, BRIIE.
    Influence of aluminium on creep strength of 9–12% Cr steels2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 527, p. 118-125Article in journal (Refereed)
    Abstract [en]

    The influence of aluminium on creep strength of 9% Cr steels is predicted by a fundamental model forcreep. Through thermodynamic modelling the particle structure is determined for a temperature andcomposition range. This shows how AlN is formed at the expense of MX carbonitrides of VN characterwhen the aluminium content is increased. The remaining MX particles are of NbC type and have approximatelyone fifth of the original phase fraction. The evolution in microstructure such as particle coarseningis included in the model as well as the recovery. Rupture time is predicted using a modified Norton equationincluding back-stresses calculated from microstructure. The predictions show correspondence tosome of the creep data for the steel P91 over a temperature and stress range. Furthermore, simulationwith high Al content verifies the observed early failure of Al rich components. Overall, the simulationsshow a decrease in rupture time by a factor 6 due to Al additions of up to 0.2%.

  • 47.
    Makaya, Advenit
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Study on the production of Fe–Cr–Mn–C–Si foam by nitrogen solubility difference between the liquid and solid phases2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413-414, p. 533-537Article in journal (Refereed)
    Abstract [en]

    The feasibility of the production of Fe-base metallic foam by using the nitrogen solubility difference between the liquid and austenite phases has been studied in the Fe-Cr-Mn-C-Si system. Compositions showing a suitable solubility gap for precipitation of gas pores upon solidification have been derived by thermodynamic calculations of the nitrogen solubility in the liquid and solid phases, using the interaction parameters of nitrogen. Small amount of foams were produced for different compositions. The foaming involved dissolution of chromium nitrides into the melt and subsequent quenching. Four different compositions were tested: by varying the C content between 2 and 6 wt.%, the effect of the primary carbides on the foam microstructure could be studied. The presence of those carbides appears as an important element for the promotion of the pore nucleation and the prevention of pore coalescence. The addition of SiO2 powder in some experiments illustrated the beneficial effect of a nucleating agent to reach a homogeneous distribution of the gas pores.

  • 48.
    Malik, Amer
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Yeddu, Hemantha Kumar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Three dimensional elasto-plastic phase field simulation of martensitic transformation in polycrystal2012In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 556, p. 221-232Article in journal (Refereed)
    Abstract [en]

    The Phase Field Microelasticity model proposed by Khachaturyan is used to perform 3D simulation of Martensitic Transformation in polycrystalline materials using finite element method. The effect of plastic accommodation is investigated by using a time dependent equation for evolution of plastic deformation. In this study, elasto-plastic phase field simulations are performed in 2D and 3D for different boundary conditions to simulate FCC -> BCT martensitic transformation in polycrystalline Fe-0.3%C alloy. The simulation results depict that the introduction of plastic accommodation reduces the stress intensity in the parent phase and hence causes an increase in volume fraction of the martensite. Simulation results also show that autocatalistic transformation initiates at the grain boundaries and grow into the parent phase. It has been concluded that stress distribution and the evolution of microstructure can be predicted with the current model in a polycrystal.

  • 49.
    Molnár, Dávid Sándor
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Högskolan Dalarna.
    Sun, Xun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Engberg, Göran
    Högskolan Dalarna.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, p. 490-497Article in journal (Refereed)
    Abstract [en]

    The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

  • 50.
    Neding, Benjamin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tian, Ye
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. ;Johns Hopkins Univ, Dept Mat Sci & Engn, Baltimore, MD 21218 USA..
    Ko, J. Y. Peter
    Cornell Univ, Cornell High Energy Synchrotron Source, Ithaca, NY 14853 USA.;Cornell Univ, Mat Solut Network, CHESS, Ithaca, NY USA..
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Correlating temperature-dependent stacking fault energy and in-situ bulk deformation behavior for a metastable austenitic stainless steel2022In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 832, p. 142403-, article id 142403Article in journal (Refereed)
    Abstract [en]

    In-situ high-energy synchrotron X-ray diffraction experiments during uniaxial tensile loading are performed to investigate the effect of temperature (25, 45 and 70 degrees C) on the deformation behavior of a 301 metastable austenitic stainless steel. The micromechanical behavior of the steel at the three deformation temperatures is correlated with the stacking fault energy (gamma(SF)) experimentally determined through the same in-situ X-ray experiments. The applied measurements provide a unique possibility to directly interrogate the temperature dependent gamma(SF) in relation to the active bulk deformation mechanism in a metastable austenitic stainless steel. The determined gamma(SF) is 9.4 +/- 1.7 mJ m(-2) at 25 degrees C, 13.4 +/- 1.9 mJ m(-2) at 45 degrees C and 25.0 +/- 1.1 mJ m(-2) at 70 degrees C. This relatively minor change of gamma(SF) and temperature causes a significant change of the dominant deformation mechanism in the alloy. At room temperature (25 degrees C) significant amounts of stacking faults form at 0.05 true strain, with subsequent formation of large fractions of deformation-induced alpha' and epsilon-martensite, 0.4 and 0.05, at 0.4 true strain, respectively. With increasing temperature (45 degrees C) fewer stacking faults form at low strain and thereupon also smaller alpha' - and epsilon-martensite fractions form, 0.2 and 0.025, at 0.4 true strain, respectively. At the highest temperature (70 degrees C) plastic deformation primarily occurs by the generation and glide of perfect dislocations at low strain, while at higher strain these dislocations dissociate to form stacking faults. The alpha'-martensite fraction formed is significantly less at 70 degrees C reaching 0.1 at 0.4 strain, whilst epsilon-martensite is not found to form at any strain at this temperature. The temperature-dependent mechanical behavior of the alloy is consistent with the observed dominant deformation mechanisms; the strong work hardening from the TRIP effect at low temperature, and low gamma(SF), decreases significantly with increasing temperature, and gamma(SF).

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