Phase stability of B2-ordered ZrTiHfCuNiFe high entropy alloy

Abstract In the present study, bulk equiatomic ZrTiHfCuNiFe HEA rod possessing single B2 phase was successfully synthesized by the copper mold casting. The phase stability of B2-ordered ZrTiHfCuNiFe HEA was systematically investigated in comparison with that of the amorphous phase of the same composition. The characterization of their microstructure and phase evolution after long-term annealing up to 1000 h at temperatures ranging from 500 °C to 850 °C were analyzed. Annealed at 750–850 °C, the HEA casting rod and amorphous ribbon exhibit the same predominant B2 phase and a small amount of second phase at the grain boundaries. While annealed at 600 °C and below even for prolonged annealing time 1000 h, no phase transformation is observed in the HEA casting rod with B2 phase, whereas multiple phases (i.e. (Cu,Ni) 10 (Zr,Hf) 7 , ordered HCP, B2 and FeTi) are formed in the amorphous ribbon. The B2 phase obtained by annealing amorphous ribbon at high temperature does remain its B2 structure when annealed at 600 °C again. These observations clearly indicate that B2 phase in the ZrTiHfCuNiFe HEA exhibits higher thermal stability at 600 °C and below compared with the amorphous phase of the same composition, which may be attributed to the low phase transformation temperature and coordinated long-range sluggish diffusion. The present work provides a new insight into understanding the phase stability of HEA intermetallic compound.