Pressure-induced fcc to hcp transition in Ni-based high entropy solid solution alloys

Abstract

A phase transition from the fcc to a hexagonal close-packed (hcp) structure was found in NiCoCrFe starting at 13.5 GPa and the hcp structure is quenchable to ambient pressure. Only a very small amount (<5%) of hcp phase was found in the NiCoCr ternary system up to pressure of 45 GPa and no obvious hcp phase was found in NiCoCrFePd system till to 74 GPa. Ab initio Gibbs free energy calculations indicated that pressure acts as the driving force to overcome the energy barrier for the fcc to hcp phase transformation in NiCoCrFe solid solution alloy.