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  • 1.
    Holmström, Erik
    et al.
    Sandvik Coromant R&D, SE-12680 Stockholm, Sweden..
    Lizarraga, Raquel
    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.
    Salmasi, Armin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kaplan, Bartek
    Sandvik Coromant R&D, SE-12680 Stockholm, Sweden..
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermocalc Software AB, Rasundavagen 18, SE-16967 Solna, Sweden..
    Larsson, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermocalc Software AB, Rasundavagen 18, SE-16967 Solna, Sweden..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. ppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    High entropy alloys: Substituting for cobalt in cutting edge technology2018In: Applied Materials Today, ISSN 2352-9407, Vol. 12, p. 322-329Article in journal (Refereed)
    Abstract [en]

    Cemented carbide, also known as hard metal, is one of the most outstanding composite engineering materials since its commercial introduction in the 1920s. The unique combination of strength, hardness and toughness makes cemented carbides highly versatile materials for the most demanding engineering applications. In their simplest form, these materials are composites of tungsten carbide (WC) grains that are cemented with a ductile metallic binder phase, typically cobalt. However, despite the superiority of Co as binder material, there is a long-standing need to find alternative binders due to serious health concerns that have haunted the industry for nearly 80 years. In the present study, we develop a new cemented carbide with a high entropy alloy binder phase (CoCrFeNi) from raw materials to a fully functional, coated and gradient-sintered cutting tool insert. The new hard metal with reduced Co content is designed by using first principles theory and the CALPHAD method. The cutting tool was made by pressing the new hard metal in a standard geometry, sintered to have a thin binder phase enriched surface zone, free from cubic carbides and coated with protective layers of Ti(C,N) and Al2O3. The resulting cutting insert was tested in a real machining operation and compared to a state-of-the-art reference that had Co as binder phase. The cutting tool made of the newly developed cemented carbide has an exceptionally high resistance against plastic deformation at all tested cutting speeds in the machining test, outperforming the reference insert, which shows a linear increase in edge depression when the cutting speed is increased. This result opens up the possibility to utilize the unique properties of high entropy alloys for industrial applications, in particular, as binder phase in new cemented carbides.

  • 2.
    Lattemann, Martina
    et al.
    Sandvik Coromant R&D, SE-12680 Stockholm, Sweden..
    Xie, Ruiwen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lizarraga, Raquel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Holmström, Erik
    Sandvik Coromant R&D, SE-12680 Stockholm, Sweden..
    Understanding Quality Control of Hard Metals in Industry - A Quantum Mechanics Approach2019In: Advanced Theory and Simulations, ISSN 2513-0390, Vol. 2, no 6, article id 1900035Article in journal (Refereed)
    Abstract [en]

    For many decades, the magnetic saturation of, for example, hard metals (HM) such as WC-Co-based cemented carbides, has been used as process and quality control in industry to ensure consistency of product properties. In an urge to replace cobalt as a binder phase, a demand on understanding the magnetic response as a function of composition on the atomic scale is growing. In this paper, a theoretical description of the measured weight-specific magnetic saturation of hard metals as a function of the tungsten weight fraction present in the cobalt binder phase, based on first-principle calculations, is established for standard WC-Co. The predicted magnetic saturation agrees well with the experimental one. Furthermore, it is proposed that the theoretical description can be extended to alternative and more complex binder phases which allows to transfer the production control to those hard metals.

  • 3.
    Lizarraga, Raquel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Universidad Austral de Chile, Chile.
    Structural and magnetic properties of the Gd-based bulk metallic glasses GdFe2, GdCo2, and GdNi2 from first principles2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 17, article id 174201Article in journal (Refereed)
    Abstract [en]

    A structural and magnetic characterization of Gd-based bulk metallic glasses, GdFe2, GdCo2, and GdNi2, was performed. Models for the amorphous structures for two magnetic configurations, ferromagnetic and ferrimagnetic, were obtained by means of a first-principles-based method, the stochastic quenching. In all three cases, the ferrimagnetic configuration was energetically more stable than the ferromagnetic one, in perfect agreement with experiments. In the structural analysis, radial and angle distribution functions as well as calculations of bond lengths and average coordination numbers were included. Structural properties are in good agreement with experiments and do not depend on the magnetic configuration. The distribution of magnetic moments shows that amorphous GdFe2 and GdCo2 are both ferrimagnets, with antiparallel alignment of the magnetic moments of the two magnetic sublattices, whereas Ni nearly loses its magnetic moment in amorphous GdNi2, similar to the situation in its crystalline counterpart.

  • 4.
    Lizarraga, Raquel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Holmstrom, Erik
    Sandvik Coromant R&D, SE-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75121 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Alloying effect of tungsten on the structural and magnetic properties of CoCrFeNiW high entropy alloys2018In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 9, article id 094407Article in journal (Refereed)
    Abstract [en]

    The recent observation of the hexagonal-closed-packed (hcp) phase in CoCrFeNi-based multicomponent alloys has reopened the question of phase stability in these alloys. We investigate the alloying effect of tungsten on the crystal and magnetic structures of (CoCrFeNi)(1-x)W-x high entropy alloys using density functional theory by means of the exact muffin-tin orbital method. The body-centered-cubic (bcc), face-centered-cubic (fcc), and hcp phases are investigated in two magnetic states: ferrimagnetic and paramagnetic. Below 8 at. % W the ground state of (CoCrFeNi)(1-x)W-x is the ferrimagnetic hcp phase and above that, the ferrimagnetic bcc phase is stabilized. Our calculations show that the fcc and hcp phases are energetically very close in the whole range of studied W compositions and because CoCrFeNi and (CoCrFeNi)(0.93)W-0.07 are observed in the fcc phase at room temperature, the hcp-fcc structural phase transition is expected to occur at lower temperatures. The total magnetic moment in bcc is almost double the value calculated for the fcc and hcp structures, which is due to that Cr moments are nearly quenched in bcc but are coupled antiferromagnetically to Fe, Ni, and Co in both hcp and fcc. We calculated also the Curie temperature of these alloys using the mean-field approximation. The calculated value was found to be 155 K for fcc CoCrFeNi, in excellent agreement with experiments, and the addition of W decreases this value. Our results contribute to the development of these relatively unknown corrosion-resistant materials into industrial applications, such as cemented carbides.

  • 5.
    Lizarraga, Raquel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Pan, Fan
    KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Bergqvist, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Holmstrom, Erik
    Gercsi, Zsolt
    Vitos, Levente
    First Principles Theory of the hcp-fcc Phase Transition in Cobalt2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 3778Article in journal (Refereed)
    Abstract [en]

    Identifying the forces that drive a phase transition is always challenging. The hcp-fcc phase transition that occurs in cobalt at similar to 700 K has not yet been fully understood, although early theoretical studies have suggested that magnetism plays a main role in the stabilization of the fcc phase at high temperatures. Here, we perform a first principles study of the free energies of these two phases, which we break into contributions arising from the vibration of the lattice, electronic and magnetic systems and volume expansion. Our analysis of the energy of the phases shows that magnetic effects alone cannot drive the fcc-hcp transition in Co and that the largest contribution to the stabilization of the fcc phase comes from the vibration of the ionic lattice. By including all the contributions to the free energy considered here we obtain a theoretical transition temperature of 825 K.

  • 6.
    Tian, Liyun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lizárraga, Raquel
    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.
    Holmström, E.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    A first principles study of the stacking fault energies for fcc Co-based binary alloys2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 136, p. 215-223Article in journal (Refereed)
    Abstract [en]

    The stacking fault energy is closely related to structural phase transformations and can help to understand plastic deformation mechanisms in materials. Here we perform first principles calculations of the stacking fault energy in the face centered cubic (fcc) Cobalt-based binary alloys Co1−x Mx, where M = Cr, Fe, Ni, Mo, Ru, Rh, Pd and W. We investigate the concentration range between 0 and 30 at.% of the alloying element. The results are discussed in connection to the phase transition between the low-temperature hexagonal close packed (hcp) and the fcc structures observed in Co and its alloys. By analyzing the stacking fault energies, we show that alloying Co with Cr, Ru, and Rh promotes the hcp phase formation while Fe, Ni and Pd favor the fcc phase instead. The effect of Mo and W on the phase transition differs from the other elements, that is, for concentrations below 10% the intrinsic stacking fault energy is lower than that for pure fcc Co and the energy barrier is higher, whereas above 10% the situation reverses. We carry out also thermodynamic calculations using the ThermoCalc software. The trends of the ab initio stacking fault energy are found to agree well with those of the molar Gibbs energy differences and the phase transition temperature in the binary phase diagrams and give a solid support for the phase stability of these alloys.

  • 7.
    Wang, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Dept Chemical Engineering, Northeast Electric Power University, Jilin, 132012, China.
    Hou, Ziyong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Lizarrága, Raquel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tian, Ye
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Babu, Prasath
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Holmström, Erik
    Coromant R & D, SE-12680, Stockholm, Sweden.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermo-Calc Software, Råsundav. 18, SE-16767, Solna, Sweden.
    Larsson, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. Thermo-Calc Software, Råsundav. 18, SE-16767, Solna, Sweden.
    An experimental and theoretical study of duplex fcc+hcp cobalt based entropic alloys2019In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 176, p. 11-18Article in journal (Refereed)
    Abstract [en]

    Martensitically formed duplex fcc + hcp Co-based entropic alloys have been investigated both experimentally and theoretically. Theoretical predictions are in good agreement with experimental observations. A fair correlation is found between calculated driving forces for a partitionless fcc→hcp transformation and experimentally obtained phase fractions.

  • 8.
    Xie, Ruiwen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lizárraga, Raquel
    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.
    Hou, Ziyong
    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.
    Lattemann, M.
    Holmström, E.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Quantum mechanics basis of quality control in hard metals2019In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 169, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Non-destructive and reliable quality control methods are a key aspect to designing, developing and manufacturing new materials for industrial applications and new technologies. The measurement of the magnetic saturation is one of such methods and it is conventionally employed in the cemented carbides industry. We present a general quantum mechanics based relation between the magnetic saturation and the components of the binder phase of cemented carbides, which can be directly employed as a quality control. To illustrate our results, we calculate the magnetic saturation of a binder phase, 85Ni15Fe binary alloy, using ab-initio methods and compare the theoretical predictions to the magnetic saturation measurements. We also analyse interface and segregation effects on the magnetic saturation by studying the electronic structure of the binder phase. The excellent agreement between calculations and measurements demonstrates the applicability of our method to any binder phase. Since the magnetic saturation is employed to ensure the quality of cemented carbides, the present method allows us to explore new materials for alternative binder phases efficiently.

1 - 8 of 8
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