Shock Induced Order-disorder Transformation in Ni3Al

TL;DR

This paper models the shock-induced order-disorder transition in Ni3Al using a first-principles-based EOS, revealing a transition at 205 GPa and a high melting point, with implications for high-pressure metallurgy and Earth sciences.

Contribution

It introduces a cluster expansion and CVM-based EOS model to analyze phase transitions in Ni3Al under shock compression, highlighting configurational effects over electronic excitations.

Findings

Order-disorder transition at 205 GPa and 3750K.

High melting temperature of 6955K at the same pressure.

Configurational contributions dominate over electronic excitations.

Abstract

The Hugoniot of Ni3Al with L12 structure is calculated with an equation of state (EOS) based on a cluster expansion and variation method from first principles. It is found that an order-disorder transition occurs at a shock pressure of 205GPa, corresponding to 3750K in temperature. On the other hand, an unexpected high melting temperature about 6955K is obtained at the same pressure, which is completely different from the case at ambient pressure where the melting point is slightly lower than the order-disorder transition temperature, implying the high pressure phase diagram has its own characteristics. The present work also demonstrates the configurational contribution is more important than electronic excitations in alloys and mineral crystals within a large range of temperature, and an EOS model based on CVM is necessary for high pressure metallurgy and theoretical Earth model.