Ab Initio Study of Stability, Local Order, and Phase Diagram For a Series of bcc-based Transition Metal Alloys
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Ab Initio Study of Stability, Local Order, and Phase Diagram For a Series of bcc-based Transition Metal Alloys P. E. A. Turchi1 • V. Drchal2 • J. Kudrnovsky2 • A. Perron1
Submitted: 18 May 2020 / in revised form: 13 August 2020 / Accepted: 4 September 2020 Ó ASM International 2020
Abstract A parameter-free electronic structure approach is applied to the study of stability and chemical order in the 15 substitutional body-centered cubic (bcc)-based alloys made of the six transition metals of groups 5 (V, Nb, Ta) and 6 (Cr, Mo, W) of the periodic table. The method is based on a Green’s function description of the electronic structure of the random alloys. Configurational order is treated within the generalized perturbation method, and temperature effects are examined with a generalized meanfield approach. In contrast to the results summarized in the assessed phase diagrams, stability and ordering trends are predicted in a broad range of alloy composition for at least
This article is an invited paper selected from presentations at ‘‘PSDK XIV: Phase Stability and Diffusion Kinetics—Gibbs: Phase Equilibria, Diffusion and Materials Design’’ held during MS&T’19, September 29–October 3, 2019, in Portland, Oregon. The special sessions were dedicated to honor Dr. Patrice Turchi, recipient of the ASM International 2019 J. Willard Gibbs Phase Equilibria Award ‘‘for outstanding and pioneering contributions in the application of first-principles, quantum–mechanical calculations to the modeling of phase equilibria and thermodynamic behavior of alloys.’’ It has been expanded from its original presentation. & P. E. A. Turchi [email protected] V. Drchal [email protected] J. Kudrnovsky [email protected] A. Perron [email protected] 1
Lawrence Livermore National Laboratory, Livermore, CA 94550
2
Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Praha 8, Czech Republic
seven alloys, and explanation is found in their electronic structure properties. Short-range order results, thermodynamics analysis, and bcc-based phase diagrams are also presented. Keywords ab initio methods metallic alloys phase diagram stability
1 Introduction Much attention has been paid to alloys made of refractory transition metals (TM) of groups 5 (V, Nb, Ta) and 6 (Cr, Mo, W) of the periodic table (also referred to as columns VA and VIA in the old IUPAC labels), and in particular, Nb, Mo, Ta, and W that display high melting points. In this manuscript, the alloy notation is based on the group and period of the elements, i.e., V-Nb, V-Ta, V-Cr, V-Mo, V-W, Nb-Ta, Nb-Cr, Nb-Mo, Nb-W, Ta-Cr, Ta-Mo, Ta-W, Cr-Mo, Cr-W, and Mo-W. These alloys show excellent strength at elevated temperature and therefore have been found useful for high-temperature space and nuclear applications, among other applications. According to the fifteen reported phase diagrams,[1] most substitutional alloys should display complete solubility in the solid phase with a bcc (or a) crystalline structure before melting, except for the existence of a Laves ph
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