Order-disorder Effects on Equation of State in FCC Ni-Al Alloys

TL;DR

This study investigates how order-disorder phenomena influence the equation of state properties in Ni-Al alloys using the cluster variation method, revealing a unique 'W shape' variation linked to configurational effects.

Contribution

It introduces a novel analysis of order-disorder effects on EOS properties in Ni-Al alloys using ab initio based CVM, highlighting the impact of configurational ordering on thermodynamic behavior.

Findings

Thermal expansion, heat capacity, and Gruneisen parameter show a 'W shape' variation with composition.

Order-disorder effects can influence local fractures in alloys and crystals.

Inverse Hessian matrix elements dominate the observed property variations.

Abstract

Order-disorder effects on equation of state (EOS) properties of substitutional binary alloys are investigated with the cluster variation method (CVM) based on ab initio effective cluster interactions (ECI). Calculations are applied to the fcc based Ni-Al system. Various related quantities are shown to vary with concentration around stoichiometry with a surprising "W shape", such as the thermal expansion coefficient, the heat capacity and the Gruneisen parameter, due to configurational ordering effects. Analysis shows that this feature originates from the dominated behavior of some elements of the inverse of Hessian matrix. For the first time we point out that the strong compositional variation of these properties might be partially responsible for local fractures in alloys and mineral crystals under heating, highlighting the importance of subtle thermodynamic behavior of order-disorder systems.