The effects of annealing on severely cold-rolled equiatomic HfNbTiZr high entropy alloy.

• The precipitation hardening effect is pronounced when specimens are aged. • HCP precipitates can form when specimens are aged. • The hardness of the specimens increases as the recrystallization temperature increases. • Hall-Petch relation of HfNbTiZr RHEA is established. In this study, the effects of annealing on mechanical properties and phase evolution of 80% cold-rolled equiatomic HfNbTiZr high entropy alloy (HEA) are studied. A single BCC-phase solid solution is identified in the as cold-rolled and the recrystallized state at above 700°C, and its hardness increases as the annealing temperature increases. However, the HEA still follows the Hall–Petch equation according to tensile tests. When the HfNbTiZr HEA is annealed at 450°C, hardness would increase, while the hardening effect on 550°C annealed specimens is not so pronounced. The age hardening effect is mainly associated with the formation of HCP precipitates. [ABSTRACT FROM AUTHOR]