Phase stability enhancement in AlMo0.5NbTa0.5TiZr refractory high entropy alloy through Re addition

In this research, the influence of Re addition on the thermal stability of the AlMo0.5NbTa0.5TiZr refractory high-entropy alloy was investigated. The based alloy (Re-free) has a microstructure consisted of body-centered cubic (BCC) and hexagonal close-packed (HCP) phases. This dual-phase microstructure was thermally instable and decomposed into a multiphase microstructure during aging treatment in the temperature range of 1000–1200 °C. In contrast, the Re-containing alloy exhibited significantly improved phase stability under the similar aging condition. The enhanced phase stability was attributed to the decelerated atomic diffusion, resulting from the addition of Re. While the segregation of Zr and consequent formation of large needle-like HCP precipitates were the major drawbacks in the microstructure of the aged base alloy, those phases were effectively restricted by the addition of Re, so that only spherical fine precipitates appeared in the microstructure of the aged Re-containing alloy. It turned out that the formation of new precipitates in the aged alloys substantially affects the hardness.