Thermodynamics of the Cr-Ta-W system by combining the ab initio and CALPHAD methods

Larry Kaufman, P. E.A. Turchi, Weiming Huang, Zi Kui Liu

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Abstract

The thermodynamic properties of alloys can be described from the knowledge of the underlying lattice and the atomic numbers of the alloy species by using a first-principles electronic structure approach based on the tight-binding linear muffin-tin orbital method within the coherent potential approximation (TB-LMTO-CPA) and the local density approximation of density functional theory. The generalized perturbation method (GPM) permits direct mapping of the configurational part of the effective one-electron Hamiltonian onto an Ising-like model thus insuring the necessary link between quantum mechanics and statistical thermodynamics. To test the practical application of this approach to multi-component alloys, data assessment has been successfully performed for the Cr-Ta-W alloy system by using the thermodynamic results derived from the TB-LMTO-CPA-GPM and the cluster variation method (CVM) in the tetrahedron approximation for Ta-W alloys as functions of temperature and concentration. These later results predict B2 ordering for the bcc-based Ta-W system with a maximum ordering temperature near 1000 K at 43 at.%. Ta. The output thermodynamics were converted to a Redlich-Kister/Bragg-Williams format with an acceptable level of accuracy. The results were then combined with those of the CALPHAD description of the Cr-W and Cr-Ta systems to calculate isothermal sections of the ternary phase diagram of the Cr-Ta-W system.

Original languageEnglish (US)
Pages (from-to)419-433
Number of pages15
JournalCalphad: Computer Coupling of Phase Diagrams and Thermochemistry
Volume25
Issue number3
DOIs
StatePublished - Sep 2001

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All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Computer Science Applications

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