Effects of annealing on the microstructural evolution and phase transition in an AlCrCuFeNi₂ high-entropy alloy

An AlCrCuFeNi₂ high entropy alloy (HEA) was prepared by arc melting, followed by annealing at different temperatures. The elemental distributions, phase formation, morphology and microstructural evolution of the HEA in both the as-cast state and annealed state were investigated. The results indicate that the HEA undergoes elements segregation, precipitation and spinodal decomposition. The as-cast alloy consists of Cr-Fe-Ni rich FCC dendritic (DR) phase and BCC interdendritic (ID) phase. Spherical Fe-Cr rich BCC precipitates were found to disperse in Al-Ni rich B2 (ordered BCC) matrix. After heat treatments, the distribution of elements clearly changes, along with changes of the constituent phase and morphology. After annealing at 600°C, the DR region remains Cr-Fe-Ni rich phase, while some spherical precipitates transform into the needle-like structure within the ID region. The L1₂ (ordered FCC) nanorod-shaped phase ((Ni,Cu)₃Al) and plate-like Al-Ni rich phase form within the DR region when annealing up to 900°C. The L1₂ phase almost dissolves in the FCC matrix due to the order-disorder transition and an obvious coarsening of the Fe-Cr rich phase occurs after annealing at 1100°C. The segregation of Cu atoms at the interface between DR and ID regions is found at the as-cast state, while a uniform distribution of Cu atoms in DR and ID regions was observed after annealing at 1100°C.