Formation and evolution of metastable BCC phase during solidification of CoCrFeNi high-entropy alloy

The formation and evolution of metastable BCC phase during the solidification of CoCrFeNi HEA is studied by molecular dynamics (MD) method. It is found that the primary phase is mainly combined by stable FCC atoms under the cooling rate of 0.5 K/ps, while few metastable BCC atoms are observed during the nucleation and growth process. Under the cooling rate of 0.5 K/ps, the metastable FCC nuclei inside with bulk BCC structures and HCP twinning planes are formed during the primary nucleation and the metastable BCC phases gradually transform into stable FCC phase during the growth of nuclei, and few BCC phases is retained in the solidified solids. It is also found that the volume fraction of metastable BCC phases decreases with the reduction of cooling rate, and the formation and evolution of metastable BCC phases in CoCrFeNi HEA are different from that in some conventional metals and alloys.