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  • 1.
    Malik, Amer
    et al.
    KTH.
    Yeddu, Hemantha Kumar
    KTH.
    Amberg, Gustav
    KTH.
    Borgenstam, Annika
    KTH.
    Ågren, John
    KTH.
    Three dimensional elasto-plastic phase field simulation of martensitic transformation in polycrystal2012Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 556, s. 221-232Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    Tahir, Abdul Malik
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Do-Quang, Minh
    KTH.
    Initial rapid wetting in metallic systems2013Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, nr 14, s. 5375-5386Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial rapid wetting of a solid surface by a liquid phase is an important step in many industrial processes. Liquid-phase sintering of powder metallurgical steels is one such industrial process, where metallic powders of micrometer size are used. Investigating the dynamic wetting of a high-temperature metallic drop of micrometer size experimentally is very challenging. Here, a phase-field-based numerical model is first implemented and verified by accurately capturing the initial dynamic wetting of millimeter-sized metal drops and then the model is extended to predict the dynamic wetting of a micrometer-sized metal drop. We found, in accordance with recent observations, that contact line friction is required for accurate simulation of dynamic wetting. Our results predict the wetting time for a micrometer-sized metal drop and also indicate that the dynamic wetting patterns at the micro- and millimeter length scales are qualitatively similar. We also found that the wetting process is much faster for a micrometer-sized metal drop compared to a millimeter-sized metal drop.

  • 3.
    Tahir, Abdul Malik
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Hedström, Peter
    KTH.
    Bergman, O.
    Höganäs AB.
    Chasoglou, D.
    Swerea KIMAB AB.
    Frisk, K.
    Swerea KIMAB AB.
    Behaviour of master alloy during sintering of PM steels: redistribution and dimensional variations2015Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 58, nr 2, s. 133-141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The addition of alloying elements in low alloyed PM steels in the form of a master alloy gives the advantage of introducing oxidation sensitive but less expensive elements and also allows manipulation in composition adjustment to achieve desired properties. In this work, interrupted sintering trials of the Fe-2MA-0.5C (%) (MA = Cu based master alloy) are performed. The behaviour of the liquid forming master alloy, for instance in terms of liquid phase formation, alloying element redistribution and effect on the dimensional changes, is investigated. The results show that master alloy particles melt over a range of temperature, which is also supported by the thermodynamic calculations. The low swelling in the master alloy system, compared to a reference system of Fe-2Cu-0.5C, is attributed to the progressive melting of the master alloy. The mean diffusion distance of Cu in Fe at the interparticle boundaries is 5.8 mu m after 34 min of isothermal holding.

  • 4.
    Tahir, Abdul Malik
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Hedström, Peter
    KTH.
    Bergman, Ola
    Höganäs AB.
    Frisk, Karin
    Swerea KIMAB AB.
    Cu redistribution during sintering of Fe–2Cu and Fe–2Cu–0·5C compacts2014Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 57, nr 5, s. 373-379Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effective use of alloying elements in powder metallurgical steels requires a deep understanding of their redistribution kinetics during sintering. In this work, interrupted sintering trials of Fe–2Cu and Fe–2Cu–0·5C compacts were performed. Moreover, diffusion simulations of Cu in γ-Fe using Dictra were performed. It is found that transient liquid phase penetrates the Fe interparticle and grain boundaries in less than 3 min of holding time. However, C addition limits the penetration of liquid Cu, particularly into grain boundaries of large Fe particles. The results also show that the mean diffusion distance of Cu in γ-Fe in the C added system is slightly lower than that in the C-free system at 3 min of holding time; however, after 33 min, the mean diffusion distance is similar in both systems. The diffusion distances of Cu in γ-Fe, predicted by Dictra, are in good agreement with the measured values.

  • 5.
    Tahir, Abdul Malik
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Hedström, Peter
    KTH.
    Bergman, Ola
    Höganäs AB.
    Frisk, Karin
    Swerea KIMAB AB.
    Investigation of Cu distribution and porosity in Fe-2Cu and Fe-2Cu-0.5C compacts2013Inngår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013, EPMA , 2013, Vol. 2, s. 291-296Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The distribution of the alloying element Cu in steel compacts is important in determining the properties of the sintered products. In this work, mixtures of Fe-2Cu and Fe-2Cu-0.5C were compacted at 600 MPa and sintered at 1120oC for the holding times of ts= 3, 13, 23, and 33 min. Dilatometry and light optical microscopy is used to investigate porosity, Cu distribution and its effect on the dimensional changes during sintering. The result shows that the molten Cu penetrates into the Fe interparticle and grain boundaries in less then 3 min holding time at 1120°C, however C addition hinders the liquid penetration of Cu. Furthermore, it is found that the C-added compact has lower volume expansion and porosity compared to the C-free system, after 33 min of holding time at 1120°C.

  • 6.
    Villanueva, Walter
    et al.
    Institute of Standards & Technology (NIST), Gaithersburg, USA.
    Boettinger, W. J.
    National Institute of Standards & Technology (NIST), Gaithersburg, USA.
    Warren, J. A.
    Institute of Standards & Technology (NIST), Gaithersburg, USA.
    Amberg, Gustav
    KTH.
    Effect of phase change and solute diffusion on spreading on a dissolving substrate2009Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 57, nr 20, s. 6022-6036Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dissolutive wetting is investigated numerically using a diffuse-interface model that incorporates fluid flow, solute diffusion and phase change. A range of materials parameters are investigated: (1) permitting recovery of the hydrodynamic limit by suppressing the dissolution of the substrate and (2) evaluating the role of diffusion. The time history of droplet size, droplet concentration and angles between the interfaces are given. For cases in which convection dominates, the dynamics of spreading agrees with a known hydrodynamic model for spreading of inert fluids. A phase change increases wetting speed, due to a condensation that takes place near the triple junction. There is also a strong dependence of the wetting kinetics on the solute diffusivities. Details of composition changes during spreading are also discussed, such as the composition path of the bulk liquid probed at different locations in the drop. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

  • 7.
    Yeddu, Hemantha Kumar
    et al.
    KTH.
    Malik, Amer
    KTH.
    Ågren, John
    KTH.
    Amberg, Gustav
    KTH.
    Borgenstam, Annika
    KTH.
    Three-dimensional phase-field modeling of martensitic microstructure evolution in steels2012Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, nr 4, s. 1538-1547Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work a 3-D elastoplastic phase-field (PF) model is developed, based on the PF microelasticity theory proposed by A.G.Khachaturyan and by including plastic deformation as well as anisotropic elastic properties, for modeling the martensitic transformation (MT) by using the finite-element method. PF simulations in 3D are performed by considering different cases of MT occurring in an elastic material, with and without dilatation, and in an elastic perfectly plastic material with dilatation having isotropic as well as anisotropic elastic properties. As input data for the simulations the thermodynamic parameters corresponding to anFe–0.3%C alloy as well as the physical parameters corresponding to steels acquired from experimental results are considered. The simulation results clearly show auto-catalysis and morphological mirror image formation, which are some of the typical characteristics of a martensitic microstructure. The results indicate that elastic strain energy, anisotropic elastic properties, plasticity and the external clamping conditions affect MT as well as the microstructure.

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