Structural stability and thermal expansion of TiTaNbMoZr refractory high entropy alloy

Abstract

A near-equiatomic TiTaNbMoZr refractory high entropy alloy (RHEA) was prepared by vacuum arc melting. It consists of two BCC solid solution phases (predominant and minor phase are named as B-major and B minor, respectively) at room temperature. Structural stability and thermal expansion were investigated using in-situ synchrotron XRD and dilatometry. B-major phase is observed until 1273 K, whereas B-minor phase is present up to 1173 K. Above 1173 K, the formation of B ' phase is observed. The mean lattice coefficient of thermal expansion (alpha(l)m) and the mean dilatometric coefficient of thermal expansion (alpha(m)(dil)) are derived in the range of 323-1173 K and 323-1273 K, respectively. alpha lm increases linearly in the range of (8.1-8.8)x 10(-6) K-1 and the mean alpha(m)(dil) varies from 7.5 x 10(-6) K-1 to 10.9 x 10(-6) K-1. Dilatometric strain and lattice strain are found to be identical up to 1000 K. However, beyond 1000 K, the dilatometric strain increases considerably in comparison to the lattice strain due to the generation of temperature-induced point defects (vacancies). The present work demonstrates that the TiTaNbMoZr RHEA exhibits structural (phase) stability up to 1173 K and thermal stability up to 1000 K. (C) 2021 Elsevier B.V. All rights reserved.