Hierarchical phase separation of equiatomic CoCuFeNiTi high-entropy alloy during spark plasma sintering

Recently, multi-component multi-principal element alloys or high-entropy alloys have generated interesting scientific curiosity. Many of these single-phase solid solutions are found to undergo fascinating phase transformation, leading to formation of dual or even multiphase microstructure. In the present investigation, a nanoscale phase separation of equiatomic mechanically alloyed CoCuFeNiTi FCC phase is reported with detailed microstructural characterization at all length scales. The single-phase FCC alloy is found to first undergo phase separation to BCC (Ti) solid solution and FCC (Co, Cu, Ni)-rich solid solution, which again separates into two new FCC phases: (Cu, Ni) and (Co, Fe) solid solutions. The microstructural analyses using SEM, TEM and 3DAPT indicate phase separation at even atomic level. This phase separation is further probed using SAXS and SANS techniques, providing the length scales of phase separation. Interestingly, the scattering results corroborate found the results from microstructural investigations. The microstructural evolution has been modeled using phase-field model, showing similar phase separation.