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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, Materials Science and Engineering.
    Nygårds, Mikael
    KTH, Superseded Departments, 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. 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.

  • 8.
    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%.

  • 9.
    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.

  • 10. 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.

  • 11.
    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.

  • 12.
    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.

  • 13. Eriksson, C. L.
    et al.
    Larsson, Per-Lennart
    KTH, Superseded Departments, 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.

  • 14.
    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.

  • 15.
    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.

  • 16.
    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.

  • 17.
    Ganchenkova, Marija G
    et al.
    KTH, Superseded Departments, 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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    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.

  • 21.
    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.

  • 22. 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)
  • 23.
    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

  • 24. 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

  • 25.
    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.

  • 26.
    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)
  • 27.
    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.

  • 28.
    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.

  • 29.
    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.

  • 30. 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.

  • 31.
    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.

  • 32. 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)
  • 33.
    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%.

  • 34.
    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.

  • 35.
    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.

  • 36.
    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.

  • 37.
    Nygårds, Mikael
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Micromechanical modeling of ferritic/pearlitic steels2002In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 325, no 1-2, p. 435-443Article in journal (Refereed)
    Abstract [en]

    A two-dimensional micromechanical model based on the Voronoi algorithm is presented to model two-phase ferritic/pearlitic steels. Special care is taken to generate periodic grain structures as well as periodic finite element meshes. The model is evaluated by generalized plane strain finite element calculations, periodic representative cells are generated with the desired volume fraction pearlite. Loading by an arbitrary combination of average stresses or strains is possible by application of periodic boundary conditions. Uniaxial tension tests are performed on pure ferrite and pearlite specimens, as well as on materials containing 25 and 58% pearlite. Modeling of the two-phase materials was performed by using the stress-strain curves of the pure phases, in the description of the plastic properties. Comparisons between generated data and experiments at a loading strain of 2% show good agreement. Moreover, local stresses and strains are studied within the different unit cells. In addition, the model is used to investigate the plastic behavior under biaxial loading. It is shown that Hill's yield criterion gives a good fit to the numerical data.

  • 38.
    Núñez, Eugenia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Garcia, P
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gedde, Ulf
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Crystallisation behavior and crystal rearrangement of poly(ethylene oxybenzoate)2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413/414, no Sp. Iss. SI, p. 435-441Article in journal (Refereed)
    Abstract [en]

    One complex fact of polymer crystallisation is that polymer crystals have a tendency to rearrange with time. In this paper, poly(ethylene oxybenzoate)s (PEOB) with different degrees of polymerisation ranging from 5 to 30 have been studied by differential scanning calorimetry and polarised microscopy. The samples showed a great tendency for crystal rearrangement during heating to the melting point, even at high heating rates. The relationship between melting point and crystallisation temperature was analyzed and the Hoffman-Weeks method was found to be unsuitable for determining the equilibrium melting point of these polymers. It is proposed that fast crystal rearrangement, which is a characteristic feature of poly(ethylene oxybenzoate), is the reason for the inadequacy of the Hoffman-Weeks method to obtain reliable estimates of the equilibrium melting point. Polarised microscopy showed, remarkably in view of the low molar mass of the polymers, the formation of perfect banded spherulites. Linear growth rate data suggested that the branched polymers crystallised more slowly than their linear analogues, presumably due to differences in the equilibrium melting point.

  • 39.
    Petersson, Anders
    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.
    Modelling WC-Co sintering shrinkage - Effect of carbide grain size and cobalt content2007In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 452, p. 37-45Article in journal (Refereed)
    Abstract [en]

    Phenomenological models based on the constitutive parameters uniaxial viscosity, viscous equivalent of Poisson's ratio and sintering stress are used to describe WC-Co sintering shrinkage. Shrinkage is divided into three subsequent stages. The influences of carbide grain size and cobalt content are accounted for and model parameters numerically adjusted to dilatometer results. The model successfully represents published shrinkage data for different materials and milling procedures.

  • 40. Pettersson, N.
    et al.
    Wessman, S.
    Thuvander, M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Pettersson, R. F. A.
    Hertzman, S.
    Nanostructure evolution and mechanical property changes during aging of a super duplex stainless steel at 300°C2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 647, p. 241-248, article id 32735Article in journal (Refereed)
    Abstract [en]

    The nanostructure evolution and the corresponding changes in mechanical properties of a super duplex stainless steel 2507 (UNS S32750) during aging at 300. °C up to 12,000. h have been investigated. Microstructural studies using transmission electron microscopy and atom probe tomography show that subtle Cr concentration fluctuations develop during aging. The amplitude of the concentration fluctuations is proportional to the hardness of the ferrite phase, and it is also proportional to the decrease in room temperature impact toughness during aging. The fracture behaviour of the alloy changes gradually from ductile to cleavage fracture, upon aging. The cracks were found to propagate through the ferrite phase, partly along deformation twin interfaces, and delamination between the austenite and ferrite phases was observed.

  • 41.
    Pettersson, Niklas
    et al.
    Swerea KIMAB AB, Sweden.
    Frisk, K.
    Fluch, R.
    Experimental and computational study of nitride precipitation in a CrMnN austenitic stainless steel2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 84, no 27, p. 435-441Article in journal (Refereed)
    Abstract [en]

    The austenitic CrMnN stainless steels are high-strength, tough, and non-magnetic, and are used in oil field applications. The steels have high alloying contents, and precipitation of Cr-nitrides and/or intermetallic phases can occur when cooling through the temperature region 950–700 °C. The nitride precipitates appear in the grain boundaries but can be difficult to observe in the microstructure due to their small size. However, there is an effect of precipitation on corrosion and impact strength and a modelling approach to predict precipitation is valuable for alloy and process development. In the present work precipitation simulations were applied to a CrMnN steel composition, and coupled to experimental investigations after heat treatments at 700 and 800 °C. The early stages, with short heat-treatment times, were studied. The simulations were performed using TC-PRISMA, a software for calculation of multiphase precipitation kinetics, using multicomponent nucleation and growth models. Dedicated thermodynamic and kinetic databases were used for the simulations. The main precipitate was identified by experiments and simulations to be the Cr2N nitride, and the precipitation during isothermal heat treatments was investigated. Isothermal precipitation diagrams are simulated, and the influence of precipitation kinetics on toughness is discussed.

  • 42.
    Pilhagen, Johan
    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.
    Influence of nickel on the toughness of lean duplex stainless steel welds2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 602, p. 49-57Article in journal (Refereed)
    Abstract [en]

    Three weldments with the nickel contents 13, 4.9 and 6.0 wt% were made from 30 mm LDX 2101((R)) plates. The weldments were subjected to tensile, impact and fracture toughness testing. The aim was to evaluate the susceptibility for brittle failure in the weld metal at sub-zero temperatures (degrees C). The amount of ferrite was higher for the 1.3 wt% nickel weldment compared to the other two which had similar phase composition and mean free ferrite distance. The result from the tensile testing showed that for the weldment with the highest nickel content the ductility remained unchanged with decreasing temperature while the other two weldments became less ductile with decreasing temperature. J-integral based fracture toughness testing showed a significant difference in the susceptibility for brittle failure with higher values for the weldment with 6 wt% nickel than for the others with lower nickel content.

  • 43.
    Pilhagen, Johan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sieurin, Henrik
    Scania CV AB, Södertälje, Sweden.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Fracture toughness of a welded super duplex stainless steel2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 606, p. 40-45Article in journal (Refereed)
    Abstract [en]

    Fracture toughness testing was conducted on standard single-edge notched bend bar specimens of base and weld metal. The material was the SAF 2906 super duplex stainless steel. The aim was to evaluate the susceptibility for brittle failure at sub-zero temperatures for the base and weld metal. The base metal was tested between -103 and -60. °C and was evaluated according to the crack-tip opening displacement method. The fracture event at and below -80. °C can be described as ductile until critical cleavage initiation occurs, which caused unstable failure of the specimen. The welding method used was submerged arc welding with a 7. wt% nickel filler metal. The welded specimens were post-weld heat treated (PWHT) at 1100. °C for 20. min and then quenched. Energy-dispersive X-ray spectroscopy analysis showed that during PWHT substitutional element partitioning occurred which resulted in decreased nickel content in the ferrite. The PWHT weld metal specimens were tested at -72. °C. The fracture sequence was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture.

  • 44.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Electronic transport properties of quasicrystals: the unique case of the magnetoresistance2000In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 294, p. 458-463Article in journal (Refereed)
    Abstract [en]

    The magnetoresistance (MR) is but one of several anomalies in electronic transport properties of quasicrystals. However, it is an exceptional one since only in this case a large part of the results can be quantitatively described within an existing theoretical framework. Evidence is discussed that quantum interference effects (QIE) describe observations in alloys with resistivity rho (4 K) less than or equal to 0.1 Omega cm. This is useful fur understanding electronic transport in quasicrystals. Examples of information derived from QIE are given.

  • 45. Razumovskii, I. M.
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Logunov, A. V.
    Larionov, V. N.
    Ospennikova, O. G.
    Poklad, V. A.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    New generation of Ni-based superalloys designed on the basis of first-principles calculations2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 497, no 1-2, p. 18-24Article in journal (Refereed)
    Abstract [en]

    A new approach to the design of Ni-based single crystal superalloys is proposed. It is based on a concept that under given structural conditions, the creep-rupture characteristics of superalloys are mainly determined by interatomic bonding given by the cohesive energy. In order to characterize the individual contribution of each alloying element to the strength properties at high temperature, we introduce a parameter, X, which is the partial molar cohesive energy of an alloy component. This parameter is then obtained in the total energy first-principles calculations for a usual set of alloying elements. We demonstrate that creep-rupture characteristics of alloys indeed correlate with the total gain partial molar cohesive energy due to alloying and find that W, Ta, and Re have the highest values of X, and should therefore play the major role in providing high-temperature strength of superalloys. Based on this finding, we design three new superalloys with a high content of W and show that they have superior creep-rupture properties compared not only with their counterparts with the lower content of W, but also with the best Ru-bearing Ni-based superalloys.

  • 46.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Formation of a dislocation back stress during creep of copper at low temperatures2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 700, p. 622-630Article in journal (Refereed)
    Abstract [en]

    Copper gives creep strain versus time curves at 75 °C that look very similar to those recorded at much higher temperatures. Thus, for example, an extended secondary stage where the strain rate is constant is observed. Considering the high creep exponent that can be up to 75, one would expect a creep curve with rapidly increasing strain rate but that is not found. The difference to creep of pure metals at high temperatures is so large that we can talk about an entirely new material class with respect to creep. To explain the observations a recently developed dislocation model (Sandstrom, 2017) for cell structures is used. A new creep model is presented where a back stress based on the dislocations in the cell walls is introduced. Unbalanced sets of dislocations without matching dislocations of opposite signs are formed in the cell walls. Since the unbalanced content is not exposed to static recovery, it forms a stable back stress. It is shown that the computed back stress can fully explain the observations and reproduce both creep curves and results for slow strain rate tensile tests.

  • 47.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    The role of cell structure during creep of cold worked copper2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, p. 318-327Article in journal (Refereed)
    Abstract [en]

    In previous work it was demonstrated that cold work could reduce the creep rate of phosphorus doped copper (Cu-OFP) by up to six orders of magnitude at 75 degrees C at a given applied stress. Cu-OFP will be used in canisters for final disposal of spent nuclear fuel. A dislocation model for the cell structure in the cold deformed material has been formulated. A distinction is made between the balanced dislocation content in the cell walls where the number of dislocations of opposite sign match and the unbalanced content where they do not. The recovery rate of the unbalanced content is much lower than that of the balanced content. Taking this into account, it has been possible to model the creep curves of both 12% and 24% cold worked Cu-OFP. The general appearance of the two sets of creep curves are distinctly different, which can be explained by the higher recovery rate in the 24% deformed state.

  • 48.
    Sandström, Rolf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. Swerea KIMAB, Sweden.
    Wu, R.
    Hagström, J.
    Grain boundary sliding in copper and its relation to cavity formation during creep2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 651, p. 259-268Article in journal (Refereed)
    Abstract [en]

    The nucleation of creep cavities, which control the creep ductility is assumed to take place by grain boundary sliding. To determine the grain boundary sliding rate at longer testing times than previously available in the literature, two creep tests have been performed at constant loading rate at 125. °C for oxygen free copper with phosphorus (Cu-OFP). The tests were interrupted after certain strains and the amount of grain boundary sliding (GBS) was measured on flat polished surfaces. The observed amount of GBS per unit strain was 20 to 65 μm. This is of the same order of magnitude as for published tensile tests (Pettersson, 150 and 200. °C) and short time creep tests (Ayensu and Langdon, 400-600. °C). The amount of GBS was modelled based on previously performed FEM investigations. For conditions corresponding to the experiments a value of 52. μm was obtained.A model by Lim for cavity nucleation at junctions between cell and grain boundaries has been adapted to oxygen free pure copper Cu-OF and Cu-OFP. The results show that the gain in free energy at cavity nucleation is much larger for Cu-OF than for Cu-OFP implying that Cu-OF is much more prone to cavity formation. The modelled difference in free energy gain is sufficient to quantitatively explain the much higher creep ductility in Cu-OFP than in Cu-OF.

  • 49.
    Sieurin, Henrik
    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, Materials Technology.
    Austenite reformation in the heat-affected zone of duplex stainless steel 22052006In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 418, no 1-2, p. 250-256Article in journal (Refereed)
    Abstract [en]

     The aim of the present work was to evaluate the amount of reformed austenite in the heat-affected zone (HAZ) of submerged arc welded (SAW) duplex stainless steel 2205. The model is based on calculations of the nucleation and growth of austenite. The present results are compared with other studies to evaluate the toughness properties and the probability of precipitation of brittle, intermetallic sigma phase. The results indicate that cooling the weld in air provides a satisfactory amount of reformed austenite and prevents formation of sigma phase.

  • 50.
    Sieurin, Henrik
    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.
    Sigma phase precipitation in duplex stainless steel 22052007In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 444, no 1-2, p. 271-276Article in journal (Refereed)
    Abstract [en]

    Sigma phase precipitation is known to embrittle duplex stainless steel. Accordingly, heat treatment and welding must be performed carefully. Nucleation and diffusional growth of sigma phase in the duplex stainless steel 2205 have been analysed in order to ensure the high toughness shown in previous studies for both base and weld material. A quasi-static growth model has been modified in order to take into account interactions with neighbouring particles due to overlapping diffusion fields (soft impingement). The model gives a satisfactory estimate of sigma phase precipitated both during isothermal aging and continuous cooling.

12 1 - 50 of 74
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