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  • 101.
    Ma, Taoran
    et al.
    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, Physical Metallurgy.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Masood, Ansar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgh, I.
    Blomqvist, A.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Self-organizing nanostructured lamellar (Ti,Zr)C - A superhard mixed carbide2015In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 51, p. 25-28Article in journal (Refereed)
    Abstract [en]

    A nanoindentation and first-principles calculation study of a self-organizing nanostructured lamellar (Ti,Zr)C powder has been performed. The nanoindentation measurements reveal that the hardness of the carbide is comparable to the hardest transition metal carbides that have been reported previously. The origin of the super-high hardness is postulated to be due to the inherent bond strength and the large coherency strains that are generated when the carbide demixes within the miscibility gap. The high hardness is maintained at a high level even after 500 h aging treatment at 1300°C. Therefore, it is believed that the new superhard mixed carbide has a high potential in various engineering applications such as in bulk cemented carbide and cermet cutting tools, and in surface coatings.

  • 102.
    Malik, Amer
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    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.
    Effect of external loading on the martensitic transformation - A phase field study2013In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 20, p. 7868-7880Article in journal (Refereed)
    Abstract [en]

    In this work, the effect of external loading on the martensitic transformation is analyzed using an elasto-plastic phase field model. The phase field microelasticity theory, incorporating a non-linear strain tensor and the effect of grain boundaries, is used to study the impact of applied stresses on an Fe-0.3%C polycrystalline alloy, both in two and three dimensions. The evolution of plasticity is computed using a time-dependent equation that solves for the minimization of the shear strain energy. Crystallographic orientation of the grains in the polycrystal is chosen randomly and it is verified that the said assumption does not have a significant effect on the final volume fraction of martensite. Two-dimensional (2-D) and three-dimensional (3-D) simulations are performed at a temperature significantly higher than the martensitic start temperature of the alloy with uniaxial tensile, compressive and shear loading, along with hydrostatic stresses. It is found that the 3-D simulations are necessary to investigate the effect of external loading on the martensitic transformation using the phase field method since the 2-D numerical simulations produce results that are physically incorrect, while the results obtained from the 3-D simulations are in good agreement with the empirical observations found in the literature. Finally, it is concluded that the given model can be used to predict the volume fraction of martensite in a material with any kind of external loading.

  • 103.
    Malik, Amer
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    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.
    Phase field modeling of martensitic transformation- Effect of grain and twin boundariesManuscript (preprint) (Other academic)
    Abstract [en]

    In this work we are presenting, for the first time, the elasto-plastic phase field modeling and simulation of the martensitic transformation in a polycrystalline material including the effect of grain and twin boundaries. The phase field microelasticity theory proposed by Khachaturyan is used to perform 2D and 3D simulations of FCC$\rightarrow$BCT martensitic transformation in an Fe-0.3\%C polycrystalline alloy, incorporating the effect of both coherent and incoherent boundaries. The effect of plastic accommodation is also introduced into the model, by solving a time dependent equation, during the solid-to-solid phase transformation. It is found that the given phase field model, with the effect of grain boundaries, not only respects the morphological features of martensite but it also conforms well with the physics of the problem. Different sets of simulations are performed to validate the model and it is concluded that the given model can correctly predict the evolution of martensitic microstructure in a polycrystal as opposed to the previous models where the effects of grain and twin boundaries are neglected.

  • 104.
    Malik, Amer
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    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.
    Phase-field modelling of martensitic transformation: the effects of grain and twin boundaries2013In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 21, no 8, p. 085003-Article in journal (Refereed)
    Abstract [en]

    In this work, we present the non-linear elasto-plastic phase-field model and simulation of the martensitic transformation in a polycrystalline material including the effects of grain and twin boundaries. The phase-field microelasticity theory proposed by Khachaturyan is used to perform 2D and 3D simulations of fcc -> bct martensitic transformation in a Fe-0.3%C polycrystalline alloy, incorporating the effect of both coherent and incoherent boundaries. The effect of plastic accommodation is also introduced into the model, by solving a time-dependent equation, during the solid-to-solid phase transformation. It is found that the given phase-field model, with the effect of grain boundaries, not only respects the morphological features of martensite but also conforms well with the physics of the problem. Different sets of simulations are performed to validate the model and it is concluded that the given model can correctly predict the evolution of the martensitic microstructure in a polycrystal, as opposed to previous models where the effects of grain and twin boundaries are neglected.

  • 105.
    Malik, Amer
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effects of external stresses on the martensitic transformation in a 3D polycrystalline material using the phase field method2013In: Materials Research Society Symposium Proceedings: Proceedings of the Multiscale Materials Modeling 2012 Conference, Materials Research Society, 2013, p. 62-68Conference paper (Refereed)
    Abstract [en]

    In the current study an elasto-plastic phase field (PF) model, based on the PF microelasticity theory proposed by A.G. Khachaturyan, is used to investigate the effects of external stresses on the evolution of martensitic microstructure in a Fe-0.3%C polycrystalline alloy. The current model is improved to include the effects of grain boundaries in a polycrystalline material. The evolution of plastic deformation is governed by using a time dependent Ginzburg-Landau equation, solving for the minimization of the shear strain energy. PF simulations are performed in 2D and 3D to study the effects of tension, compression and shear on the martensitic transformation. It has been found that external stresses cause an increase in the volume fraction of the martensitic phase if they add to the net effect of the transformation strains, and cause a decrease otherwise. It has been concluded that the stress distribution and the evolution of martensitic microstructure can be predicted with the current model in a polycrystalline material under applied stresses.

  • 106.
    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.

  • 107.
    Mannesson, Karin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    WC grain growth during sintering of cemented carbides: Experiments and simulations2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cemented carbides are composite materials consisting of a hard carbide and a ductile binder. They are powdermetallurgically manufactured, where liquid-phase sintering is one of the main steps. The most common cemented carbide consists of WC and Co and it is widely used for cutting tools. Two of the most important factors controlling the mechanical properties are the WC grain size and the grain size distribution and thus it is of great interest to understand the grain growth behavior.

    In this thesis the grain growth during sintering at 1430 °C is studied both experimentally and through computer simulations. The grain growth behavior in cemented carbides cannot be explained from the classical LSW-theory. The WC grains have a faceted shape necessitating growth by 2-D nucleation of new atomic layers or surface defects. A new model based on 2-D nucleation, long-range diffusion and interface friction is formulated.

    Three powders having different average sizes are studied and both experiments and simulations show that a fine-grained powder may grow past a coarse-grained powder, indicating that abnormal grain growth has taken place in the fine-grained powder. Fine-grained powders with various fractions of large grains are also studied and it is seen that a faster growth is obtained with increasing fraction of large grains and that an initially slightly bimodal powder can approach the logaritmic normal distribution after long sintering times.

    The grain size measurements are performed on 2-D sections using image analysis on SEM images or EBSD analysis. Since the growth model is based on 3-D size distributions the 2-D size distributions have to be transformed to 3-D, and a new method, Inverse Saltykov, is proposed. The 2-D size distribution is first represented with kernel estimators and the 3-D size distribution is optimized in an iterative manner. In this way both negative values in the 3-D size distribution and modifications of the raw data are avoided.

  • 108.
    Mannesson, Karin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    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.
    Carbide grain growth: the effect of grain size distributionsManuscript (preprint) (Other academic)
    Abstract [en]

    It is important to understand the WC grain growth behavior in order to obtain good mechanical properties when manufacturing cemented carbides. In the present study the WC grain growth for dierent initial grain size distributions during sintering is studied theoretically using a model based on three processes; 2-D nucleation of atomic planes, long-range diusion and interface friction. Simulations clearly show that the initial grain size distribution inuences the growth behavior significantly. Bimodal powders show a more dramatic grain growth than powders having a lognormalgrain size distribution.

  • 109.
    Mannesson, Karin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgh, Ida
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    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.
    Abnormal grain growth in cemented carbides - Experiments and simulations2011In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 29, no 4, p. 488-494Article in journal (Refereed)
    Abstract [en]

    The grain size and the grain size distribution are two of the most important factors when tailoring the mechanical properties of cemented carbides. In the present work the effect on the growth behavior when adding some abnormal grains in an initial fine grained powder is studied. It is clearly seen that abnormal grains in a fine grained matrix lead to faster grain growth and a higher average grain size.

  • 110.
    Mannesson, Karin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Elfwing, Mattias
    Kusoffsky, Alexandra
    Norgren, Susanne
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Analysis of WC grain growth during sintering using electron backscatter diffraction and image analysis2008In: International Journal of Refratory metals and Hard Materials, ISSN 0263-4368, Vol. 26, no 5, p. 449-455Article in journal (Refereed)
    Abstract [en]

    The WC carbide grain size is important for the technological properties of cemented carbide cutting tools. in the present work the WC carbide grain size distribution is determined after milling and sintering for 0.25, 1 and 8 h at 1430 degrees C. The WC grain size distribution, both for the powder after milling and the sintered specimens, is determined by two different methods, i.e. image analysis on scanning electron microscopy (SEM) images and electron backscatter diffraction (EBSD). It should be noted that in this work the 2D grain size distribution is considered. The EBSD analysis clearly shows that the special 12 boundaries are present in the powder and that their fraction decreases during sintering and particularly during the early stages. When the 12 boundaries are omitted in the EBSD analysis the results of the grain size measurements for the two methods agree quite well.

  • 111.
    Mannesson, Karin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jeppsson, Johan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    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.
    Carbide grain growth in cemented carbides2011In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 5, p. 1912-1923Article in journal (Refereed)
    Abstract [en]

    Abnormal grain growth is often observed in cemented carbides during sintering, but cannot be understood in terms of the classical LSW theory. In this work the grain growth behavior during sintering at 1430 °C is studied both experimentally and by means of computer simulations. A model based on several processes—2-D nucleation of growth ledges, mass transfer across the interface and long-range diffusion coupled in series—is formulated and the equations are solved numerically. Both computer simulations and experimental studies reveal that the grain growth behavior is strongly influenced by the initial size distribution.

  • 112. Mason, Paul
    et al.
    Engström, Anders
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hallström, Samuel
    Simulation of diffusion in surface and interface reactions2010In: ASM Handbook, vol 22B: Materials process simulation / [ed] D.U. Furrer and S.L. Semiatin, ASM International, 2010, p. 586-599Chapter in book (Other academic)
    Abstract [en]

    Historically, the field of materials science and engineering has focused on establishing the processing-structure- property relationships of materials through experimental trial and error with an understanding of the influence of microstructure—the microstructure, processing, and chemistry all being directly related to the crystallography, kinetics, and thermodynamics of the materials. In comparatively recent years, as computational methods have evolved, it has been possible to predict some such properties and relationships through numerical simulation.

  • 113.
    Masood, Ansar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Oak, J. J
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Excellent bulk forming ability and high plasticity of Biocompatible Titanium based bulk metallic glassesManuscript (preprint) (Other academic)
    Abstract [en]

    A series of bulk glassy alloys of Ti-Zr-Cu-Pd-Sn composition without toxic elements (Ni, Be, Al) were investigated that revealed excellent bulk forming ability by exhibiting large supercooled regions (ΔTx≥56K), high values of  reduced glass transition temperature (Trg ≥0.56) and the γ parameter (γ ≥ 0.39). As a consequence of large ΔTx≈70K glassy rods of at least 14mm diameter of Ti38.5Zr11.2Cu33.2Pd14.3Sn2.8 (Ti15) alloy were fabricated by direct Cu-mold casting. Uniaxial compressive test performed at room temperature showed high fracture strength (≥2070MPa) and good plasticity (≥5.8%) for all studied alloys. High bulk forming ability along with excellent plasticity (~6.8%) of Ti38.5Zr11.2Cu33.2Pd14.3Sn2.8 (Ti15) alloy as compare to other toxic free titanium based bulk metallic glasses (BMGs) makes it a potential candidate for biomedical application point of view. 

  • 114.
    Masood, Ansar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effect of Ni-substitution on glass forming ability, mechanical, and magnetic properties of FeBNbY bulk metallic glasses2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 1, p. 013505-Article in journal (Refereed)
    Abstract [en]

    We present a method to identify bulk glass forming ability by partial substitution of Fe by Ni in FeBNbY based amorphous alloy ribbons and as a consequence obtain enhanced mechanical and soft magnetic properties of bulk glassy rods of diameter as large as 4.5 mm. A detailed investigation of thermal, mechanical, and magnetic properties of (Fe0.72-x NixB0.24Nb0.04)(95.5)Y-4.5 alloys (with x similar to 0.02, 0.04, 0.06, 0.08, 0.1) was carried out. The supercooled regime (Delta T-x) and other glass forming parameters, e. g., reduced glass transition temperature (T-rg), the gamma (gamma) parameter, etc., were found to be enhanced due to the Ni substitution resulting in improvement of glass forming ability (GFA). The maximum values of such parameters (Delta T-x similar to 94 K, T-rg similar to 0.644, and gamma similar to 0.435) were obtained for the alloy with x similar to 0.06, making it possible to cast cylindrical rods with 4.5 mm diameter for this composition. Nanoindentation studies on glassy rods also point out that (Fe0.66Ni0.06B0.24Nb0.04)(95.5)Y-4.5 alloy exhibit the maximum value of hardness (H similar to 12 GPa) as well as elastic modulus (E similar to 193 GPa) among all of these samples. In addition to these, that particular sample shows the lowest room temperature coercivity (H-c similar to 210 mOe). By annealing at 823 K, H-c can be further reduced to 60 mOe due to its structural relaxation. We attribute the improved soft magnetic and mechanical properties of as-quenched (Fe0.66Ni0.06B0.24Nb0.04)(95.5)Y-4.5 alloy to higher packing density attained due to its large glass forming ability.

  • 115.
    Masood, Ansar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tamaki, Takahiko
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    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.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    A New Class of Materials for Magneto-Optical Applications: Transparent Amorphous Thin Films of Fe-B-Nb and Fe-B-Nb-Y Metallic Glassy Alloys2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 4, p. 4004005-Article in journal (Refereed)
    Abstract [en]

    Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb- and Fe-B-Nb-Y-based glassy metal targets were grown on quartz substrates by pulsed laser deposition, and their optical and magneto-optical properties were investigated over the visible spectrum (400-700 nm). All the films found to be fully amorphous in structure were continuous with uniform thickness and surface morphology. Their optical transmittance in the range 50%-85% was found to be film thickness dependent over the entire visible regime. The Verdet constant (V) and Faraday rotation angle (theta(f)) for different films (similar to 4-18 nm) investigated as a function of wavelength (lambda) show considerably higher values for the films of Fe-B-Nb-Y alloy as compared with those for Fe-B-Nb films, e. g., the similar to 4 nm film of Fe-B-Nb-Y alloy exhibits V similar to 49 degrees/Oe cm and theta(f)similar to 26 degrees/mu m while it decreased to similar to 29.4 degrees/Oe and similar to 11.8 degrees/mu m, respectively, for the Fe-B-Nb alloy at lambda=611 nm. A linear relationship is found for the wavelength dependence of V and theta(f) for both alloy systems. To the best of our knowledge, these values are considerably higher than those reported for any other magneto-optic material. The films are found to be soft magnetic with a high saturation moment while their magnetic coercivity values increases with thinness of the films. The observed combination of optical and magneto-optical properties of this new class of amorphous metallic films makes them viable for multifunctional magneto-optical applications.

  • 116.
    Miotti Bettanini, Alvise
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Welding of high performance metal matrix composite materials: the ICME approach.2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The material development cycle is becoming too slow if compared with other technologies sectors like IT and electronics. The materials scientists’ community needs to bring materials science back to the core of human development. ICME (Integrated Computational Materials Engineer) is a new discipline that uses advanced computational tools to simulate material microstructures, processes and their links with the final properties. There is the need for a new way to design tailor-made materials with a faster and cheaper development cycle while creating products that meet “real-world” functionalities rather than vague set of specifications. Using the ICME approach, cutting edge computational thermodynamics models were employed in order to assist the microstructure characterization and refinement during the TIG welding of a functionally graded composite material with outstanding wear and corrosion resistance. The DICTRA diffusion model accurately predicted the carbon diffusion during sintering, Thermo-Calc and TC-PRISMA models described the thermodynamic and kinetics of harmful carbide precipitation, while COMSOL Multhiphysic furnished the temperature distribution profile at every timestep during TIG welding of the material. Bainite transformation and the influence of chromium and molybdenum was studied and modelled with MAP_STEEL software. The simulations were then compared with experimental observations and a very good agreement between computational works and experiments was found for both thermodynamic and kinetics predictions. The use of this new system proved to be a robust assistance to the classic development method and the material microstructures and processes were carefully adjusted in order to increase corrosion resistance and weldability. This new approach to material development can radically change the way we think and we make materials. The results suggest that the use of computational tools is a reality that can dramatically increase the efficiency of the material development. 

  • 117. Morral, J. E.
    et al.
    Pan, X. M.
    Zhou, N.
    Larsson, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Wang, Y. Z.
    Singularities in multiphase diffusion couples2008In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 58, no 11, p. 970-972Article in journal (Refereed)
    Abstract [en]

    Singularities are not normally expected in diffusion couple data; however, they can occur in certain multiphase concentration profiles and diffusion paths. The following work reviews the theoretical reason why singularities form and gives two different computer simulations that support the theoretical predictions. In addition, a correction is given to a previous paper in which artifacts created by modeling software were inadvertently reported as diffusional singularities.

  • 118.
    Mu, Wangzhong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Shibata, Hiroyuki
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jönsson, Pär Göran
    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.
    Ferrite Formation Dynamics and Microstructures in Inclusion Engineered Steels with Ti2O3 and TiN AdditionsManuscript (preprint) (Other academic)
    Abstract [en]

    The dynamics of intragranular ferrite (IGF) formation in inclusion engineered steels with Ti2O3 and TiN additions were investigated using in-situ high temperature confocal laser scanning microscopy (CLSM). Furthermore, the chemical composition of the inclusions and the final microstructures after continuous cooling was investigated using electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD), respectively. The results show that there is a significant effect of the chemical composition of the inclusions, the cooling rate and the prior austenite grain size on the phase fractions and the starting temperatures of IGF and grain boundary ferrite (GBF) formation. The fraction of IGF is larger in the steel with Ti2O3 addition compared to the steel with TiN addition after the same thermal cycle has been imposed. This is because the TiOx phase provides more potent nucleation sites for IGF than the TiN phase does. The fraction of IGF in the steels was highest after at an intermediate cooling rate of 70 ºC/min since competing phase transformations were avoided, however, the IGF was refined with increasing cooling rate. In addition, the IGF fraction increases and the starting temperature of GBF decreases with the increasing prior austenite grain size, however, the starting temperature of IGF keeps almost the value when the grain size changes.

  • 119.
    Mu, Wangzhong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Shibata, Hiroyuki
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jönsson, Pär
    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.
    Combination of in situ microscopy and calorimetry to study austenite decomposition in inclusion engineered steels2015In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344XArticle in journal (Refereed)
    Abstract [en]

    In situ high-temperature confocal laser scanning microscopy and differential scanning calorimetry studies of ferrite formation in inclusion engineered (Ti2O3 and TiN) steels have been performed. The applied methodology allows distinction between intragranular ferrite, grain boundary ferrite, and pearlite. The effect of the inclusions and cooling rates on the initiation of phase transformation and the final microstructure is discussed. It is concluded that the applied hybrid methodology could provide vital details of solid-state phase transformations within the field of inclusion engineering.

  • 120.
    Nabeel, Muhammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Frykholm, R.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Influence of alloying elements on Ni distribution in PM steels2014In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 57, no 2, p. 111-118Article in journal (Refereed)
    Abstract [en]

    Powder metallurgical (PM) steels with elemental Ni additions exhibit non-homogenous microstructures with soft Ni rich areas, lean in C, after conventional sintering. Though, the exact correlation between the distribution of Ni and mechanical properties is not well known and depends on the conditions, e.g. the load state, it is desirable to be able to control the distribution of Ni since it plays a major role in the properties of Ni PM components. By introducing other alloying elements, the microstructure homogeneity of Ni containing PM steels, can be influenced. Thus, the effect of common alloying elements on the homogeneity of sintered microstructures has been investigated in the present work. It is found that additions of either C or Mo have minor effect on Ni distribution in the Fe-Ni system. However, addition of both C and Mo to Fe-Ni improves the Ni distribution. In addition, a strong interaction between Ni and Cu is observed and it enhances the Ni homogeneity. Furthermore, the influence of Cu is more pronounced in presence of C.

  • 121.
    Nabeel, Muhammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Extreme Value Distribution of clusters in REM-alloyed stainless steelsManuscript (preprint) (Other academic)
    Abstract [en]

    An extreme value distribution (EVD) analysis has been applied for three dimensional (3D) investigations of clusters observed in REM alloyed stainless steel samples. The presence of observed unit areas without any clusters has been discussed. It has been shown that an increase of the observed unit area (AO) significantly improves the correlation of EVD regression lines. Moreover, three different size parameters were considered for EVD analysis. The results show that using the maximum length of clusters (LC) results in a better correlation of EVD regression lines by improving R2 value up to 0.9876 as compared to 0.9656 – 0.9774 for other size parameters. Moreover, a comparison of predicted and observed maximum lengths of clusters showed that there is need of further work on validation of EVD analysis. 

  • 122.
    Nabeel, Muhammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Friction Forces and Mechanical Dust Generation in an Iron Ore Pellet Bed Subjected to Varied Applied Loads2017In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 57, no 4, p. 656-664Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets degrade and generate dust during transportation and handling as well as during the iron making process. This leads to material losses and effects the process efficiency in a negative manner. In order, to reduce the generation of dust it is important to understand the influence of process parameters on the dust formation. An experimental setup was used to measure the dust generation and friction forces caused by abrasion of iron ore pellets in a closed pack bed. A varied load of 1 to 3 kg was applied on the pellet bed but at a constant air flow rate to capture the airborne dust particles. It was observed that an increase of similar to 67% is observed in the friction and the dust generation in the bed as the applied load increased from 1 to 3 kg. Moreover, the evaluation of the particle size distribution of the generated dust showed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. Moreover, it has been shown that in an air flow the morphology and the orientation of dust particles can influence the air velocity required to transport the particles upwards.

  • 123.
    Nabeel, Muhammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Glaser, Bjoern
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Characterization of dust generated during mechanical wear of partially reduced iron ore pelletsManuscript (preprint) (Other academic)
    Abstract [en]

    During reduction in a blast furnace (BF), the iron ore pellets undergo structural changes which facilitate dust generation due to the mechanical wear / disintegration of the pellets. The generated dust decreases the permeability and productivity of the BF process. Thus, this study investigates the mechanical wear of iron ore pellets reduced at 500 °C (P500) and 850 °C (P850) and compares the results to the wear of unreduced pellets (P25). Moreover, the dust generated during the wear experiments is also characterized. It was found that pellets reduced at 500 °C exhibit a ~ 16 to 35% higher wear rate than reference unreduced pellets. For the pellets reduced at 850 °C, the mechanical wear is inhibited by a formation of a metallic layer at the outer surface of the pellets. Further, the dust generated due to mechanical wear of reduced pellets contained 3 to 6 times higher amount of coarse particles (>20µm) as compared to the dust from unreduced pellets. The obtained results are explained on the basis of the structural changes which take place during the reduction of pellets. 

  • 124. Nanesa, Hadi Ghasemi
    et al.
    Jahazi, Mohammad
    Naraghi, Reza
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Martensitic transformation in AISI D2 tool steel during continuous cooling to 173 K2015In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 50, no 17, p. 5758-5768Article in journal (Refereed)
    Abstract [en]

    Martensitic transformation of AISI D2 tool steel continuously cooled from 1303 K to the cryogenic temperature of 173 K is investigated by dilatometry using 10 or 50 K s(-1) cooling rates. A 'typical' expansion takes place from the temperature and reaches a maximum at 325 K. However, an atypical behavior is observed below this temperature implying the activation of further martensitic transformation. A modification to existing equations is proposed, which allows for more accurate description of the kinetics of martensitic transformation. Scanning electron microscopic studies indicated the presence of plate and lath martensite for both cooling rates. Carbide precipitation takes place at the rate of 10 K s(-1) before the start of martensitic transformation while it was not observed when the 50 K s(-1) rate was used. Transmission electron microscopic studies revealed that the microstructure also contains a significant amount of nano-twinned martensite.

  • 125.
    Naraghi, Reza
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Martensitic Transformation in Austenitic Stainless Steels2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Martensitic transformation is very important in austenitic stainless steels where the transformation induced plasticity phenomenon provides a combination of good mechanical properties, such as formability and strength. However, the difficulty of predicting the material behaviour is one of the major drawbacks of these steels. In order to model this behaviour it is of great importance to be able to characterize the morphology, crystallography and the amount of different types of martensite. The morphology and crystallography of thermal and deformation induced lath martensite in stainless steels were re-examined by means of optical microscopy and electron backscatter diffraction (EBSD) technique.

    The experiments were performed on AISI301, 304 and 204Cu austenitic stainless steels. Plastic deformation was carried out by means of uniaxial tensile tests at the strain rate of  to produce strain induced α’-martensite at a temperature ranging from 0 to 60ºC. An in-situ measurement of the martensite content was performed during the tensile testing using a Ferritescope to provide the necessary experimental values for modelling.

    Optical microscopy revealed the morphology of the strain induced α’-martensite as sets of thin parallel needles that go through the parent austenite grain and stop at the grain or annealing twin boundaries. Large amount of α’-martensite could be seen at the intersection of shear bands. However, considerable amount of α’-martensite was also observed when only one set of bands is activated. EBSD was successfully used to analyze the morphology and crystallography of martensite. The α’-martensite maintained the Kurdjumov-Sachs (K-S) orientation relationship with the austenite phase. Although all six possible variants did not appear within a single packet, one or two variants were often favoured out of six related to the specific {111} plane. The misorientations between the neighbouring variants were mainly <111> 60º or <110> 49.5º.

  • 126.
    Naraghi, Reza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Spontaneous and Deformation-Induced Martensite in Austenitic Stainless Steels with Different Stability2011In: STEEL RES INT, ISSN 1611-3683, Vol. 82, no 4, p. 337-345Article in journal (Refereed)
    Abstract [en]

    The fraction and microstructure of spontaneous and deformation-induced martensite in three austenitic stainless steels with different austenite stability have been investigated. Samples were quenched in brine followed by cooling in liquid nitrogen or plastically deformed by uniaxial tensile testing at different initial temperatures. In-situ ferritescope measurements of the martensite fraction was conducted during tensile testing and complemented with ex-situ X-ray diffractometry. The microstructures of quenched and deformed samples were examined using light optical microscopy and electron backscattered diffraction. It was found that annealing twins in austenite are effective nucleation sites for spontaneous alpha'-martensite, while deformation-induced alpha'-martensite mainly formed within parallel shear-bands. The alpha'-martensite formed has an orientation relationship near the Kurdjumov-Sachs (K-S) relation with the parent austenite phase even at high plastic strains, and adjacent alpha'-martensite variants were mainly twin related (< 111 > 60 degrees or Sigma 3).

  • 127.
    Naraghi, Reza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Stability of Fe-C Martensite–Effect of Zener-Ordering2011In: Proceedings of the 1st World Congress on Integrated Computational Materials Engineering (ICME) / [ed] John Allison; Peter Collins; George Spanos, United States of America: John Wiley & Sons, 2011, p. 235-240Conference paper (Refereed)
    Abstract [en]

    A model has been developed to describe thermodynamic properties of body centered tetragonal (bct) martensite and body centered cubic (bcc) states of iron-carbon interstitial solid solutions by applying (Fe)1(C,Va)1(C,Va)1(C,VA)1. The order-disorder transition in dilute solid solutions is described using experimental data, and the effect of so called Zener ordering on the stability of martensite is evaluated. From the proposed thermodynamic model it is evident that the selection of model parameters of the bcc phase has an important physical meaning related to the redistribution of carbon atoms prior to carbide precipitation (spinodal decomposition in Fe-C martensite during early stages of aging).

  • 128.
    Naraghi, Reza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Selleby, Malin
    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.
    Thermodynamics of stable and metastable structures in Fe-C system2014In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 46, p. 148-158Article in journal (Refereed)
    Abstract [en]

    The thermodynamic properties and the phase diagram of the Fe-C system are reviewed by means of the CALPHAD method and Gibbs energy functions valid from 0 K upwards are presented. The Fe-C system has been evaluated previously by Gustafson. The information on thermodynamic properties and phase equilibria have now been updated and used as a basis to re-optimize the model parameters. In addition, thermodynamic properties of metastable cementite, Hagg and eta carbides are evaluated on the basis of available experimental data and taking into account the magnetic nature of these carbides. Moreover, a model is proposed for carbon ordering phenomena in martensite. Structural changes during early stages of aging of martensite are described using the proposed model and tempering equilibria with cementite, Hagg, and eta carbides are well reproduced. It should also been mentioned that the present description represents experimental data on the equilibrium with the liquid better than Gustafson's thermodynamic description.

  • 129.
    Odqvist, Joakim
    et al.
    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.
    Xiong, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    3D analysis of phase separation in ferritic stainless steels2012In: Proceedings of the 1st International Conference on 3D Materials Science, John Wiley & Sons, 2012, p. 221-226Conference paper (Refereed)
    Abstract [en]

    The embrittlement of ferritic stainless steels during low temperature aging is attributed to the phase separation with Fe and Cr demixing. The small scale of the decomposed structure with only minor compositional fluctuations and short distances between the enriched and depleted regions has been a challenge for quite some time. A wide selection of experimental and modeling tools have been used to quantify these types of structures. These analyses often focus on rather late stages of decomposition where the mechanical properties are already seriously affected. The recent advance in 3D tools like phase-field and atom probe tomography have created a need for good quantitative procedures of evaluating the structure and also to link results from the continuum approach to the individual atom measurements. This work aims at addressing this need.

  • 130.
    Okamoto, Riki
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    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.
    Interphase precipitation in niobium-microalloyed steels2010In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 14, p. 4783-4790Article in journal (Refereed)
    Abstract [en]

    The interphase precipitation in niobium steel has been investigated. In the present work, the austenite/ferrite transformation speed should be fast due to hot deformations, and interphase precipitation can be observed after 10 s isothermal holding in the temperature range 923-1023 K. The dominant interphase precipitation is planar and is not oriented on the {1 1 0}alpha plane suggested by the ledge mechanism but on other planes.

  • 131.
    Okamoto, Riki
    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, Physical Metallurgy.
    A model for interphase precipitation based on finite interface solute drag theory2010In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 14, p. 4791-4803Article in journal (Refereed)
    Abstract [en]

    A model for interphase precipitation with the ledge mechanism, based on a eutectoid reaction, has been developed and combined with the finite interface solute drag model and a numerical solution of the diffusion equations inside the migrating phase interface. In the model, niobium flows in two directions, i.e. perpendicular to the direction of the ledge migration by eutectoid-like reaction and simultaneously parallel to the direction of the ledge migration inside the ledge interface. The difference between ledge transformation and typical phase transformation is compared using this model and the effects of row spacing, temperature and segregation energy are discussed. The calculation results using the model are compared with experimental results and the critical driving force for interphase precipitation is evaluated. The estimations of the niobium carbide precipitation using this model are in good agreement with experimental results.

  • 132.
    Okamoto, Riki
    et al.
    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.
    Assessment of niobium segregation energy in migrating ferrite/austenite phase interfaces2010In: INT J MATER RES, ISSN 1862-5282, Vol. 101, no 10, p. 1232-1240Article in journal (Refereed)
    Abstract [en]

    The effects of physical parameters on the total dissipation of Gibbs energy inside migrating ferrite/austenite interfaces have been re-investigated using Odqvist's solute drag model. It is shown that the mobility of the ferrite/austenite phase interface and the diffusivity of niobium in the interface have a strong effect on the Gibbs energy dissipation. As the phase interface mobility was recently reassessed, it is clear that the Gibbs energy of niobium segregation and the diffusivity of niobium in the interface must also be reassessed. In this paper both parameters are reassessed in the Fe-C-Nb system using new physical parameters and experimental results from ultra-low carbon steels.

  • 133. Petersson, A.
    et al.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Rearrangement and pore size evolution during WC-Co sintering below the eutectic temperature2005In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 53, no 6, p. 1673-1683Article in journal (Refereed)
    Abstract [en]

    The early stage densification during sintering of a WC-Co material has been investigated using image analysis to obtain pore size distributions of partially sintered samples. Sintering shrinkage is related to rearrangement of the WC particles. A bimodal pore size distribution develops during isothermal holding, but not during heating. A given isothermal holding results in less densification after slow heating than after fast heating. It is suggested that isothermal holding yields a more rigid compact when the equilibrium solubility is approached, and that the thermal expansion anisotropy of the WC-Co system plays a role during heating. Rearrangement was simulated with a discrete element method. The simulations suggest that microstructure evolution retards significantly as isothermal conditions are established. Attempts to introduce dissolution in the simulations failed to represent the expected increase in density.

  • 134. Petersson, A.
    et al.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Sintering shrinkage of WC-Co materials with bimodal grain size distributions2005In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 53, no 6, p. 1665-1671Article in journal (Refereed)
    Abstract [en]

    Sintering shrinkage and densification rate were investigated for WC-Co materials with different grain size distributions. Unimodal distributions were compared to bimodal mixtures with size ratio close to four. A bimodal carbide mixture with 25% fine particles showed similar shrinkage behaviour to a material with unimodal distribution around the same mean value. With 50% fine particles the initial shrinkage was slightly faster than a unimodal material with the same mean size, while the late shrinkage was considerably slower. The effects of particle size distribution on particle packing and sintering are discussed, and the effect on viscosity modelled.

  • 135. Petersson, A.
    et al.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Sintering shrinkage of WC-Co materials with different compositions2005In: International Journal of Refractory Metals & Hard Materials, ISSN 0263-4368, Vol. 23, no 06-apr, p. 258-266Article in journal (Refereed)
    Abstract [en]

    The composition of cemented carbides affects not only the properties of the finished product, but also changes the sintering behaviour. In this work the sintering of medium-coarse WC-Co materials has been investigated. Descriptions of the constitutive behaviour, uniaxial viscosity, viscous Poisson's ratio and sintering stress, obtained from dilatometry experiments under uniaxial load were extended to cover different material compositions. The proposed models were used to express the linear shrinkage rate, and the model parameters fitted to shrinkage data from materials with different carbide grain size, cobalt content and carbon content. The influence of grain size distribution was also investigated. Finally, the shrinkage rate was used to numerically integrate for sintering shrinkage under different thermal cycles.

  • 136. Philippe, T.
    et al.
    Bonvalet, Manon
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Blavette, D.
    Kinetic theory of diffusion-limited nucleation2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 20, article id 204501Article in journal (Refereed)
    Abstract [en]

    We examine binary nucleation in the size and composition space {R, c} using the formalism of the multivariable theory [N. V. Alekseechkin, J. Chem. Phys. 124, 124512 (2006)]. We show that the variable c drops out of consideration for very large curvature of the new phase Gibbs energy with composition. Consequently nuclei around the critical size have the critical composition, which is derived from the condition of criticality for the canonical variables and is found not to depend on surface tension. In this case, nucleation kinetics can be investigated in the size space only. Using macroscopic kinetics, we determine the general expression for the condensation rate when growth is limited by bulk diffusion, which accounts for both diffusion and capillarity and exhibits a different dependence with the critical size, as compared with the interface-limited regime. This new expression of the condensation rate for bulk diffusion-limited nucleation is the counterpart of the classical interface-limited result. We then extend our analysis to multicomponent solutions.

  • 137. Purdy, Gary
    et al.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Brechet, Yves
    Enomoto, Masato
    Furuhara, Tadashi
    Gamsjager, Ernst
    Goune, Mohamed
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hutchinson, Christopher
    Militzer, Matthias
    Zurob, Hatem
    ALEMI: A Ten-Year History of Discussions of Alloying-Element Interactions with Migrating Interfaces2011In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 42A, no 12, p. 3703-3718Article in journal (Refereed)
    Abstract [en]

    ALEMI is concerned with the interactions between Alloying Elements and Migrating Interfaces. A first meeting was held in conjunction with the 2000 TMS Fall Meeting in St. Louis, MO. About 22 attendees endorsed the principles contained in the invitation, which envisaged a more collaborative approach to the study of alloying element interactions with transformation interfaces, especially in alloy steels. The meetings were intended to be informal workshops emphasizing the sharing of ideas and plans for research. The development of a shared stock of alloys for research was planned, as well as the publication of summaries of discussions in an open, preferably archival, forum. Eight further meetings were held, often in conjunction with major conferences. An approximate equilibrium developed between discussions of theoretical matters and experimental results and methods. A remarkable number of those who attended the first meeting in St. Louis continued to participate. Research ideas were put forward, issues debated, collaborations fostered, and the science of transformation interfaces advanced.

  • 138.
    Rahaman, Moshiour
    et al.
    Ferritico, Brinellvagen 85, S-10044 Stockholm, Sweden..
    Mu, Wangzhong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. Ferritico, Brinellvägen 85, S-10044 Stockholm, Sweden.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ferritico, Brinellvägen 85, S-10044 Stockholm, Sweden.
    Machine Learning to Predict the Martensite Start Temperature in Steels2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 5, p. 2081-2091Article in journal (Refereed)
    Abstract [en]

    The martensite start temperature (M-s) is a critical parameter when designing high-performance steels and their heat treatments. It has, therefore, attracted significant interest over the years. Numerous methodologies, such as thermodynamics-based, linear regression and artificial neural network (ANN) modeling, have been applied. The application of data-driven approaches, such as ANN modeling, or the wider concept of machine learning (ML), have shown limited technical applicability, but considering that these methods have made significant progress lately and that materials data are becoming more accessible, a new attempt at data-driven predictions of the M-s is timely. We here investigate the usage of ML to predict the M-s of steels based on their chemical composition. A database of the M(s)vs alloy composition containing 2277 unique entries is collected. It is ensured that all alloys are fully austenitic at the given austenitization temperature by thermodynamic calculations. The ML modeling is performed using four different ensemble methods and ANN. Train-test split series are used to evaluate the five models, and it is found that all four ensemble methods outperform the ANN on the current dataset. The reason is that the ensemble methods perform better for the rather small dataset used in the present work. Thereafter, a validation dataset of 115 M-s entries is collected from a new reference and the final ML model is benchmarked vs a recent thermodynamics-based model from the literature. The ML model provides excellent predictions on the validation dataset with a root-mean-square error of 18, which is slightly better than the thermodynamics-based model. The results on the validation dataset indicate the technical usefulness of the ML model to predict the M-s in steels for design and optimization of alloys and heat treatments. Furthermore, the agility of the ML model indicates its advantage over thermodynamics-based models for M-s predictions in complex multicomponent steels. (C) The Author(s) 2019

  • 139. Ratke, L.
    et al.
    Brueck, S.
    Mathiesen, R.
    Ludwig, A.
    Gruber-Pretzler, M.
    Tonn, B.
    Gzovskyy, K.
    Granasy, L.
    Tegze, G.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Arnberg, L.
    Gust, E.
    Anger, G.
    Lauer, M.
    Garen, R.
    Reifenhaeuser, B.
    Lead-free bearing alloys for engine applications results of the ESA-MAP project MONOPHAS2007In: Transactions of the Indian Institute of Metals, ISSN 0019-493X, Vol. 60, no 2-3, p. 103-111Article in journal (Refereed)
    Abstract [en]

    Recent developments to reduce fuel consumption, emission and air pollution, size and weight of engines for automotive, truck, ship propulsion and electrical power generation lead to temperature and load conditions within engines that cannot be provided by conventional bearings. Therefore a European project has been established to develop a technically usable aluminium based lead free bearing material with sufficient hardness, wear and friction properties and good corrosion resistance to be produced with semi-continuous casting process. The paper describes the scientific challenges, approaches to tackle the solidification and casting problems and presents some illustrative research results.

  • 140.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 5, p. 054203-Article in journal (Refereed)
    Abstract [en]

    We find, using ab initio atomistic simulations of vacancy-mediated diffusion processes in TiC and ZrC, that a multivacancy self-diffusion mechanism is operative for metal-atom diffusion in substoichiometric carbides. It involves a special type of a stable point defect, a metal vacancy "dressed" in a shell of carbon vacancies. We show that this vacancy cluster is strongly bound and can propagate through the lattice without dissociating.

  • 141.
    Razumovskiy, Vsevolod
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Mat Ctr Leoben Forsch GmbH, A-8700 Leoben, Austria.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Dilner, David
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Korzhavyi, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Effect of carbon vacancies on thermodynamic properties of TiC-ZrC mixed carbides2014In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 46, p. 87-91Article in journal (Refereed)
    Abstract [en]

    Thermodynamic properties of a TiZrC mixed carbide system are investigated by first-principles methods within density functional theory. Carbon vacancies are found to have a significant contribution to the thermodynamics of TiZrC mixed carbides. The temperature effect on the thermodynamic properties of the system is calculated taking into consideration the corresponding electronic and vibrational thermal excitations.

  • 142.
    Selleby, Malin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Hillert, Mats
    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, Physical Metallurgy.
    Use of chemical potential of a compound in potential phase diagrams2011In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 35, no 3, p. 342-345Article in journal (Refereed)
    Abstract [en]

    Potential phase diagrams, where the chemical potential of a compound is used as an axis, do not obey the usual rules for potential phase diagrams. Examples are presented in order to help the interpretation of such diagrams. The thermodynamic background of the special properties is examined.

  • 143.
    Shen, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    INVESTIGATION OF THE RELATIONSHIP BETWEEN LOCAL PLASTIC STRAIN ESTIMATED BY EBSD AND LOCAL NANOINDENTATION HARDNESS IN ALLOY 6902015In: International Conference on Environmental Degradation of Materials in Nuclear Power Systems / [ed] Mike Wright, Canadian Nuclear Society , 2015Conference paper (Refereed)
    Abstract [en]

    Plastic strain distribution in Alloy 690 has been of interest since laboratory experiments showed that cold deformation may trigger susceptibility to stress corrosion cracking. In operating plants, the plastic strains in Alloy 690 generally originate from manufacturing processes, e.g. grinding, tube straightening or welding. In recent years, the plastic strains from such operations have typically been mapped using electron backscatter diffraction. This method quantifies curvature of the crystal lattice, which has been shown to correlate with plastic strain on both the macroscopic and the mesoscopic levels, and has a high enough spatial resolution to potentially show the plastic strain distribution within individual grains. In this work, the correlation between local estimated plastic strains and nanoindentation hardness has been investigated. Local estimated plastic strains were able to predict the spatial distribution of local increases and decreases in hardness, but vastly overestimated the magnitude of variation. It is believed that the calibration curve used to estimate macroscopic plastic strain from macroscopic average misorientations overestimates local plastic strains where local misorientations are high, and underestimates the strains where the local misorientations are low. A calibration curve based on local strain measurements and local misorientations could possibly be a suitable alternative.

  • 144. Shi, P. F.
    et al.
    Engström, A.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thermodynamic calculations and kinetic simulations of some advanced materials2011In: 7th International Forum on Advanced Material Science and Technology, IFAMST-7, 2011, p. 961-974Conference paper (Refereed)
    Abstract [en]

    The Thermo-Calc and DICTRA software/database/programming-interface packages, through many successful applications in the fields of Computational Thermodynamics and Kinetics, have tremendously contributed to quantitative conceptual design and processing of various advanced materials. Materials scientists and engineers can efficiently apply such unique and comprehensive tools in calculating material properties, predicting material structures and simulating material processes, which are of wide-ranging industrial and academic importance.

  • 145. Shi, Ping-Fang
    et al.
    Engström, Anders
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Qing, Chen
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Computational thermodynamics and kinetics in materials modelling and simulations2007In: Journal of Iron and Steel Research International, ISSN 1006-706X, E-ISSN 2210-3988, Vol. 14, p. 210-215Article in journal (Refereed)
  • 146.
    Stormvinter, Albin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Low Temperature Austenite Decomposition in Carbon Steels2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Martensitic steels have become very important engineering materials in modern society. Crucial parts of everyday products are made of martensitic steels, from surgical needles and razor blades to car components and large-scale excavators. Martensite, which results from a rapid diffusionless phase transformation, has a complex nature that is challenging to characterize and to classify. Moreover the possibilities for modeling of this phase transformation have been limited, since its thermodynamics and kinetics are only reasonably well understood. However, the recent development of characterization capabilities and computational techniques, such as CALPHAD, and its applicability to ferrous martensite has not been fully explored yet.

    In the present work, a thermodynamic method for predicting the martensite start temperature (Ms) of commercial steels is developed. It is based mainly on information on Ms from binary Fe-X systems obtained from experiments using very rapid cooling, and Ms values for lath and plate martensite are treated separately. Comparison with the experimental Ms of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of Ms from commercial steels.

    A major part of the present work is dedicated to the effect of carbon content on the morphological transition from lath- to plate martensite in steels. A range of metallographic techniques were employed: (1) Optical microscopy to study the apparent morphology; (2) Transmission electron microscopy to study high-carbon plate martensite; (3) Electron backscattered diffraction to study the variant pairing tendency of martensite. The results indicate that a good understanding of the martensitic microstructure can be achieved by combining qualitative metallography with quantitative analysis, such as variant pairing analysis. This type of characterization methodology could easily be extended to any alloying system and may thus facilitate martensite characterization in general.

    Finally, a minor part addresses inverse bainite, which may form in high-carbon alloys. Its coupling to regular bainite is discussed on the basis of symmetry in the Fe-C phase diagram.  

  • 147.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    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.
    Thermodynamically Based Prediction of the Martensite Start Temperature for Commercial Steels2012In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 43A, no 10, p. 3870-3879Article in journal (Refereed)
    Abstract [en]

    A thermodynamic method for predicting the martensite start temperature of commercial steels is developed. It is based mainly on information on M (s) from binary Fe-X systems obtained from experiments with very rapid cooling, and M (s) values for lath and plate martensite are treated separately. Comparison with the experimental M (s) of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of M (s) from commercial steels.

  • 148.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    A Transmission Electron Microscopy Study of Plate Martensite Formation in High-carbon Low Alloy Steels2013In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 29, no 4, p. 373-379Article in journal (Refereed)
    Abstract [en]

    The martensitic microstructures in two high-carbon low alloy steels have been investigated by classical and automated crystallographic analysis under a transmission electron microscope. It is found that the martensitic substructure changes from consisting mostly of transformation twins for 1.20 mass% carbon (C) steel to both transformation twins and planar defects on {101}(M) for 1.67 mass% C steel. In the 1.67 mass% C steel it is further found that small martensite units have a rather homogeneous substructure, while large martensite units are more inhomogeneous. In addition, the martensite units in both steels are frequently found to be of zigzag patterns and have distinct crystallographic relationships with neighboring martensite units, e.g. kink or wedge couplings. Based on the present findings the development of martensite in high-carbon low alloy steels is discussed and a schematic of the martensite formation is presented. Moreover, whether the schematic view can be applied to plate martensite formation in general, is discussed.

  • 149.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Investigation of Lath and Plate Martensite in a Carbon Steel2011In: International Conference on Solid-Solid Phase Transformations in Inorganic Materials, 2011, Vol. 172-174, p. 61-66Conference paper (Refereed)
    Abstract [en]

    Martensite in carbon steels forms in different morphologies, often referred to as lath andplate martensite. The alloy composition has a strong effect on the morphology, for instance in car-bon steels there is a morphological change of the martensite microstructure from lath martensite atlow carbon contents to plate martensite at high carbon contents. In the present work a decarburizedhigh-carbon steel, enabling the isolation of carbons' influence alone, has been studied in order to in-vestigate the changes in morphology and hardness. From the results it is concluded that there is acontinuous change of hardness with increased carbon content. The increasing hardness slows down atabout 0.6 wt%C before decreasing at higher carbon contents. This is in accordance with the change inmorphology since it was found that lath martensite dominates below 0.6 wt%C and the first units ofgrain boundary martensite and plate martensite appear above 0.6 wt%C. At high carbon contents thedominating morphology is plate martensite, but retained austenite is also present.

  • 150.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Miyamoto, G.
    Furuhara, T.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effect of Carbon Content on the Orientation Relationship between Austenite and bct-Martensite in Fe-C Alloys resolved by Electron Backscattered DiffractionManuscript (preprint) (Other academic)
12345 101 - 150 of 211
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