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  • 1.
    Linder, David
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Walbrühl, Martin
    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.
    Martensite transformation in cemented carbides with alternative binders2016In: World PM 2016 Congress and Exhibition, European Powder Metallurgy Association (EPMA) , 2016Conference paper (Refereed)
    Abstract [en]

    The recent interest in substitution of cobalt in cemented carbides has led to renewed efforts into finding alternative binders. Promising candidates are Fe and Ni-based systems which generally can be divided into austenitic (fcc) and martensitic (bct) binders. The martensitic transformation may drastically change the properties, thus, when designing an alternative binder it is important to know at what temperature and composition the martensitic transformation takes place. Furthermore, it is of interest to understand how the transformation is affected by the binder mean free path and the stresses in the binder introduced by the carbide grains. Another aspect, that is important for high temperature properties, is the tempering of martensite as well as reversion to austenite. The effect of these processes is here investigated along with how they influence the behavior of the cemented carbides at different temperatures, thereby determining their application range.

  • 2.
    Walbrühl, Martin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    ICME guided development of cemented carbides with alternative binder systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The development of alternative binder systems for tungsten carbide (WC) based cemented carbides has again become of relevance due to possible changes in EU regulations regarding the use of Cobalt (Co). A framework for the ICME (Integrated Computational Materials Engineering) based Materials Design is presented to accelerate the development of alternative binder systems.

    Part one of this work deals with the design of the cemented carbide composite hardness. It has been shown that the intrinsic binder hardness is comparable to a bulk metal alloy and that based on the binder solubilities a solid solution strengthening model developed in this work can be employed. Using a method presented in this work the non-equilibrium, frozen-in binder solubilities can be obtained. Both the design of the binder phase and composite hardness is presented based on a general Materials Design approach.

    Part two deals with a multiscale approach to model the surface gradient formation. The experimentally missing data on liquid binder diffusion has been calculated using AIMD (Ab initio Molecular Dynamics). The diffusion through the liquid cemented carbide binder has to be reduced to an effective diffusion value due to the solid carbides acting as obstacles that increase the diffusion path. The geometrical reduction of the diffusion has been investigated experimentally using the SIMS (secondary ion mass spectroscopy) technique in WC-Nickel-58Nickel diffusion couples. The geometrical contribution of the so-called labyrinth factor has been proven by the combination of the experiments and in conjunction with DICTRA simulations using the precise liquid AIMD diffusivities. Unfortunately, despite the improved kinetic database and the geometrical diffusion reduction, the surface gradient formation cannot be explained satisfactory in complex cemented carbide grades. Additional, but so far unidentified, contributions have to be considered to predict the surface gradient thickness.

  • 3.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Blomqvist, Andreas
    Sandvik Coromant R&D, SE-12680 Stockholm, Sweden..
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Atomic diffusion in liquid nickel: First-principles modeling2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 24, article id 244503Article in journal (Refereed)
    Abstract [en]

    Self- and impurity diffusion coefficients are assessed in the liquid nickel system by the fundamental ab initio molecular dynamics approach. The impurity diffusion coefficients in the Ni-X systems (X=C, Co, N, Nb, Ta, Ti, W) are mostly not available in the current literature. The simulations are performed at four temperatures, in the range from 1903 to 2303 K, which allows to extract activation energies and frequency factors for the temperature dependent diffusion coefficient assuming an Arrhenius-type behavior in the liquid. In addition to the temperature dependence, the concentration-dependent impurity diffusion was investigated for the Ni-Co system. The data are of relevance for the development of the state-of-the art Ni-based superalloys and alternative binder systems in cemented carbides. The obtained theoretical results are in very good agreement with the limited experimental data for the diffusion in liquid Ni systems.

  • 4.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Blomqvist, Andreas
    Thomen, Aurélien
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Larsson, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effective diffusion in cemented carbide systems: Geometrical effect of the labyrinth factorManuscript (preprint) (Other academic)
    Abstract [en]

    In cemented carbides the effective diffusivities are associated with the carbides acting as obstacles that increase the diffusion distance, thus altering the overall diffusion in the composite. From an industrial point of view, the prediction of the surface gradient formation is important to develop state-of-the-art cemented carbide cutting tools and require an understanding of the liquid binder diffusivities and the effective diffusion reduction at typical sintering temperatures where the binder is molten. Recently, a full description of the diffusivities in the liquid binder has become available and the focus of the present work is thus the effective diffusion reduction. Isotope diffusion couple experiments have been successfully performed to investigate the effective diffusion in a WC-Ni liquid binder-carbide composite material, i.e. a cemented carbide. The 58Ni isotope diffusion profiles have been measured with Secondary Ion Mass Spectroscopy (SIMS) and the results have been compared to DICTRA simulations using an updated kinetic database. The agreement between the experimental and simulated diffusion profiles is excellent showing that the theoretical geometrical limit, simulated with the upper Hashin-Shtrikman bound, is obeyed in simple cemented carbide systems. For complex cemented carbide systems, where gradient sintering is relevant, the effective diffusion is insufficiently explained by the geometrical reduction.

  • 5.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Linder, David
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, Royal Inst Technol, Dept Mat Sci & Engn, Unit Struct, SE-10044 Stockholm, Sweden..
    Bonvalet, Manon
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, Royal Inst Technol, Dept Mat Sci & Engn, Unit Struct, SE-10044 Stockholm, Sweden..
    Ågren, John
    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.
    ICME guided property design: Room temperature hardness in cemented carbides2019In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 161, p. 35-43Article in journal (Refereed)
    Abstract [en]

    The potential change in EU regulations may affect the traditional W-C-Co based cemented carbides industry and a methodology is required to accelerate the materials development with alternative binders. This work presents the ICME (Integrated Computational Materials Engineering) framework and the improved models that will enable tailor-made materials design of cemented carbides. The cemented carbide hardness is one of the key properties of the composites and here its close relation to the binder composition is in focus. Modeling the influence of alternative binder materials on the hardness of cemented carbides offers a way to optimize the composite properties of prospective binder candidates virtually, thereby reducing the development time and costs drastically compared to a classical trial-and-error method. The outline of a genetic algorithm is presented and the integration of the required models and tools, that are, or will become, available within this ICME framework, are presented.

  • 6.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Linder, David
    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.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    A new hardness model for materials design in cemented carbides2018In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 75, p. 94-100Article in journal (Refereed)
    Abstract [en]

    The Materials Design approach offers new possibilities towards property-oriented materials development. The performance of cemented carbides is significantly influenced by properties like the hardness and fracture toughness. Fundamentally based phenomenological models, which allow for prediction of the properties of interest, make it possible to tailor the properties of the material based on the required performance. None of the previously available models are suitable to actively design the cemented carbide hardness because they are valid only for Co binders and do not allow alternative binder phases. The hardness is greatly influenced by the chemistry, binder volume fraction and carbide grain size. Only the chemistry, specifically the binder composition, leaves the possibility to optimize the binder hardness and to exceed classical WC-Co cemented carbides. Specifically focusing on the design of the binder phase, a new binder hardness description is implemented in a modified Engqvist hardness model and allows description of a wider range of conventional and alternative systems. The model was validated for various published cemented carbide systems and is able to predict their hardness within a 10% error. The assessed systems contain classical Co binders as well as alternative, austenitic binders based on Fe, Ni and Co.

  • 7.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Linder, David
    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.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Alternative Ni-based cemented carbide binder – Hardness characterization by nano-indentation and focused ion beam2018In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 73, p. 204-209Article in journal (Refereed)
    Abstract [en]

    The nano-hardness in the alternative 85Ni-15Fe binder phase of WC cemented carbide has been investigated. High-resolution scanning electron microscopy (SEM) imaging was used to measure the projected indentation area and a general pile-up correction, confirmed on selected indents, has been employed using atomic force microscopy (AFM). Focused ion-beam (FIB) cross-sections have been used to investigate the binder morphology below the indentations and the local binder hardness has been associated to the distance to the surrounding WC grains. Generally, decreasing distance to the WC grains leads to increased binder hardness. Furthermore, the nano-hardness for the cemented carbide binder has been corrected for the indentation size effect (ISE) to obtain the corresponding macroscopic hardness. A solid solution strengthening model for multicomponent bulk alloys was used to calculate the expected binder Vickers hardness considering the binder solubilities of W and C. Both the strengthening model and the ISE corrected hardness values, for larger binder regions, are in good agreement indicating that the intrinsic binder phase hardness is similar to that of a bulk metal alloy with similar composition.

  • 8.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Linder, David
    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.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Cobalt substitution in cemented carbides guided by ICME2016In: World PM 2016 Congress and Exhibition, European Powder Metallurgy Association (EPMA) , 2016Conference paper (Refereed)
    Abstract [en]

    The increasing availability of models and growing acceptance of ICME (Integrated Computational Materials Engineering) methods may create a new attitude in materials development towards tailor-made material properties for a wide range of applications. New EU regulations may affect the traditional W-C-Co based cemented carbides. It might be necessary to replace or minimize the usage of Co and thus alternative binder materials are needed. The computational Materials Design approach offers a way to optimize the properties of prospective binder candidates virtually; reducing the development time and costs drastically compared to a classical trial-and-error method. As one of the mechanical key properties, the cemented carbide hardness is closely related to the binder material. Furthermore, the high temperature hardness is especially relevant for metal cutting applications and experimentally costly to investigate. Modelling the influence of alternative binder materials on the hardness is thus of great industrial and academic interest.

  • 9.
    Walbrühl, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Linder, David
    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.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Modelling of solid solution strengthening in multicomponent alloys2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 700, p. 301-311Article in journal (Refereed)
    Abstract [en]

    With increasing industrial interest in high alloyed multicomponent and High Entropy Alloy (HEA) systems the integration of solid solution strengthening in the ICME framework for efficient Materials Design becomes an important translator tool. A general model is proposed that performs as the framework for an extensive assessment of solid solution strengthening coefficients. The model assumes the concentration dependence of x(2/3) as proposed by Labusch but gives a non-linear composition dependence to the strengthening parameter yielding a better description for concentrated alloys. To calibrate the model, 895 alloy systems, including a wide range of elements, have been used giving a good agreement between calculated and experimental values. Additionally, a promising method is proposed to represent the temperature related softening in the investigated systems.

  • 10.
    Walbrühl, Martin
    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.
    Blomqvist, A.
    Larsson, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    ICME guided modeling of surface gradient formation in cemented carbides2018In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 72, p. 33-38Article in journal (Refereed)
    Abstract [en]

    Structural gradients are of great interest for state-of-the-art cemented carbides used in metal cutting applications. The gradient growth during sintering is controlled by the fundamental aspects of diffusion, thermodynamics and phase equilibria in systems with multiple components and phases. With the demand for binder alternatives to Co, there is a need for understanding the diffusion and thermodynamics in new materials systems. Materials development guided by ICME (Integrated Computational Materials Engineering) is a new approach that accelerates the design of tailor-made materials, assisting us to find and optimize prospective binder candidates using computational tools. The role of the thermodynamic descriptions will be briefly discussed but this work focuses on a better kinetic description. Models based on cemented carbide microstructures and fundamental understanding of kinetics will allow for a more general use of simulations of gradient formation. The diffusion of elements during sintering mainly occurs in the liquid binder phase, with the solid WC and gamma phases acting as an effective labyrinth, hindering diffusion. In this work, the liquid mobilities and the effective labyrinth factor is studied for traditional and alternative binders by combing ab initio molecular dynamics and diffusion couple experiments with CALPHAD modeling. 

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