Characterization on microstructure evolution of a bulk nanograined TiZrHfNb refractory high-entropy alloy

A bulk TiZrHfNb nanograined refractory high-entropy alloy (NG-RHEA) with an average grain size of 31.6 nm was prepared by inert gas condensation (IGC) method. In the initial as-IGC sample, it is composed of a body-centered cubic structure and an amorphous phase accounting for about 25%. Then the microstructure was regulated by annealing at 200 °C, 400 °C and 600 °C for 0.5 h. The results show that a dual-phase structure composed of body-centered cubic phase nanograins and amorphous phase was maintained below 400 °C. Significant grain growth was observed when annealed at 600 °C, with obvious phase decomposition detected. The hardness of as-IGC TiZrHfNb NG-RHEA increases from 348 HV to 432 HV after annealed at 400 °C. The relationship between microstructure and hardness was discussed. This work provides insights into the preparation and structure modulation of bulk NG-RHEAs.