Accurate complex-stacking-fault Gibbs energy in Ni3Al at high temperatures

TL;DR

This paper calculates the temperature-dependent Gibbs energy of complex stacking faults in Ni3Al using an advanced ab initio framework, revealing significant anharmonic effects and implications for understanding its high-temperature deformation behavior.

Contribution

It introduces a comprehensive ab initio method to evaluate high-temperature Gibbs energies of planar defects, including anharmonic and magnetic effects, for Ni3Al.

Findings

CSF energy decreases with temperature, especially above 1200K

Anharmonic contributions significantly affect defect energies

Higher energy barriers for cross-slip at elevated temperatures

Abstract

To gain a deeper insight into the anomalous yield behavior of Ni3Al, it is essential to obtain temperature-dependent formation Gibbs energies of the relevant planar defects. Here, the Gibbs energy of the complex stacking fault (CSF) is evaluated using a recently proposed ab initio framework [Acta Materialia, 255 (2023) 118986], accounting for all thermal contributions - including anharmonicity and paramagnetism - up to the melting point. The CSF energy shows a moderate decrease from 300K to about 1200 K, followed by a stronger drop. We demonstrate the necessity to carefully consider the individual thermal excitations. We also propose a way to analyze the origin of the significant anharmonic contribution to the CSF energy through atomic pair distributions at the CSF plane. With the newly available high-temperature CSF data, an increasing energy barrier for the cross-slip process in Ni3Al with increasing temperature is unveiled, necessitating the refinement of existing analytical models.