| Abstract Scope |
The structural stability of high entropy alloys can be compromised at intermediate temperatures, where the contribution of entropy is weakened but atomic migration remains active. In order to examine the metastability of refractory high entropy alloys in this temperature regime and shed light on the controlling factors, a series of equiatomic alloys with elements of Nb, Ti, V, Ta, Zr, and Hf are fabricated, which all exhibit a single-phase body-centered-cubic structure at homogenized states. Their phase stabilities are investigated during annealing for up to seven days at 400-700 ºC. Only a small portion of the alloys maintain stable, while majority of them, including all tested quinary alloys, experience decomposition and phase separation. The main features of structural evolution and elemental redistribution are understood by combining first-principles calculations and thermodynamic models. Formation enthalpy, especially lattice distortion energy, plays a critical role, while the impact of mixing entropy is not significant. |