Nanoindentation avalanches and dislocation structures in HfNbTiZr high entropy alloy

High temperature nanoindentation was performed on a refractory HfNbTiZr high-entropy alloy to probe the unique dislocation behaviors. Anomalous nanoindenation avalanche occurs once the load reaches a critical value of 10 mN and exceeds the elastic limit of the alloy. The depth of the plastic zone under indentation is much deeper in the sample with avalanches, and continues to deepen with the increase of testing temperature. A large fraction of mixed dislocations is formed after nanoindentation, instead of forming the long screw dislocations as in common refractory metals. Nanoindentation avalanche is induced by the sudden movement of a group of usually sluggish dislocations, which have a low mobility due to local chemical fluctuations and large lattice distortions. These results manifest a weak temperature-dependence of dislocation mobility in body-centered cubic high-entropy alloy.