Using Nb-Ni μ phase first principles results to calculate finite temperature thermodynamic properties in the Bragg-Williams approximation
Résumé
First-principles (FP) calculations of total energies for 32 different configurations of the μ phase in the binary system Nb-Ni is used with the compound energy formalism (CEF) to model finite temperatures thermodynamic properties. A comparison with Connolly Williams Method-Cluster Variation Method (CWM-CVM)calculations indicates that the CEF describes temperature dependent site occupancies as well as the CWM-CVM approximation within the temperature range of interest for applications. This result seems to indicate that the Bragg-Williams-Gorski Approximation (BWGA) used by the CEF is sufficient to describe the μ phase. A phase diagram is also calculated using the description of the μ phase derived in the present work together with an available Calphad assessment for the other phases of this system. CEF and CVM description of the single phase properties as a function of composition and temperature are striking similar. This approach allows a great improvement of the description of the thermodynamical properties as a function of composition compared to the calphad procedure generally used up to now. It is expected that the CEF description of the μ phase derived from first-principles energetics will yield more reliable extrapolations into higher-order systems.
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