Ab initio prediction of vacancy energetics in HCP Al-Hf-Sc-Ti-Zr high entropy alloys and the subsystems

Abstract

We perform ab initio density-functional-theory (DFT) calculations to investigate the vacancy formation and migration energies in HCP Al-Hf-Sc-Ti-Zr high entropy alloys (HEAs) and their subsystems from binaries to quinaries. For the vacancy formation properties, we utilize the special quasi-random structure approach in conjunction with a statistical analysis, from which temperature-dependent formation Gibbs energies as well as averaged atomic environments can be extracted. We show that the temperature-dependent vacancy formation Gibbs energy due to configurational excitations has a negative configurational entropy contribution. For the vacancy migration barriers, obtained from the nudged elastic band method, we apply the local cluster expansion technique to the kinetically resolved activation barriers to explore extended vacancy migration phase spaces. The local chemical environment effect and general trends in terms of the “high entropy” effect are analyzed.