Unconventional energetics of small vacancy clusters in BCC high-entropy alloy Nb0.75ZrTiV0.5

The stability of small vacancy clusters including divacancy, trivacancy and tetravacancy has been stud-ied in body-centered cubic high-entropy alloy Nb0.75ZrTiV0.5 in structures of random solid solution and short-range order by first-principles calculations and molecular dynamics simulations. Different from con-ventional body-centered cubic metals, the tightly bound configurations have a lower structural stability and are not preferred energetically in the studied high-entropy alloy. Instability of vacancy configurations leads to vacancy-atom exchanges that favor less compact configurations. The formation energy of small vacancy clusters is much smaller than its constituent elements of Nb and V due to the large structural adjustment induced by severe local lattice distortion. The difference in local lattice distortion and elemen-tal arrangement in the vacancy neighborhood leads to significant site-to-site variation in vacancy cluster energy and configuration. The formation energy has a strong correlation with the local energy state of the vacancy configuration and the extent of structural relaxation. Compared to random solid solution, the structure of short-range order has a higher stability for the most compact cluster configurations and tends to have higher vacancy cluster formation energy. According to classical molecular dynamics simu-lations of cluster diffusion at high temperature, the studied high-entropy alloy has a higher probability of cluster dissociation compared to Nb and V. The unconventional energetics of small vacancy clusters is expected to have a profound impact on their generation, diffusion, dissociation, coalescence, as well as the defect microstructure evolution during irradiation.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The stability of small vacancy clusters in a high-entropy alloy Nb0.75ZrTiV0.5 with body-centered cubic structure was investigated using first-principles calculations and molecular dynamics simulations. The tightly bound configurations were found to have lower structural stability and were not energetically preferred in the studied alloy. The instability of these configurations led to vacancy-atom exchanges that favored less compact configurations. The formation energy of small vacancy clusters was much smaller than that of its constituent elements due to the large structural adjustment induced by severe local lattice distortion. The difference in local lattice distortion and elemental arrangement in the vacancy neighborhood resulted in significant site-to-site variation in vacancy cluster energy and configuration. The unconventional energetics of small vacancy clusters are expected to have a profound impact on their behavior and the defect microstructure evolution during irradiation.