A study on the severely cold-rolled and annealed quaternary equiatomic derivatives from quinary HfNbTaTiZr refractory high entropy alloy

Abstract

The malleability, phase stability and grain growth kinetics of the quaternary equiatomic derivatives from quinary HfNbTaTiZr refractory high entropy alloy cold-rolled with 80% thickness reduction and annealed under different conditions were investigated. By excluding the poor malleability of the HfTaTiZr and NbTaTiZr alloys and the appearance of two phase in the HfNbTaZr alloy, the grain growth kinetics of the HfNbTiZr and HfNbTaTi alloys were further studied. The grain growth exponent n, kinetic constant k and activation energy for grain growth QG of the HfNbTiZr and HfNbTaTi alloys are calculated. The kinetic constant can be expressed by the Arrhenius equation with QG, which is attributed to the diffusion coefficient. It is demonstrated that the alloying element Ta with the lowest self-diffusion coefficient among these five elements would remarkably decelerate grain boundary migration, thereby hindering grain growth and increasing QG value.