EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Recent experimental studies report that several body-centered cubic (bcc) refractory high-entropy alloys (HEAs) exhibit transition-induced plasticity (TRIP) by transforming to the hexagonal close-packed (hcp) structure, which would be beneficial for better ductility. On the other hand, there are also the reports of the ω phase precipitates in bcc HEAs, which would cause embrittlement. It is therefore crucial to better understand phase transitions of such HEAs to further improve their mechanical properties. We study thermodynamic and dynamic stability of bcc refractory HEAs based on ab initio simulations. We first demonstrate that, in atomistic simulations, careful analysis for relaxed structures of bcc HEAs is essential. With the developed proper analysis of structural relaxation, the bcc–hcp phase stability is found to be closely connected to the TRIP composition in Ti–Zr–Nb–Hf–Ta-based HEAs observed in experiments. The obtained bcc–hcp equilibrium composition of these HEAs also show a substantial correlation to the valence-electron concentration (VEC). We also show that thermodynamic integration in combination with machine-learning interatomic potentials enables us to accurately compute the vibrational free energies of HEAs even near the melting temperature.