Phase separation and microhardness of rapidly solidified high-entropy CoCrFeNiCux alloys

Abstract The metastable phase separation and physical property of rapidly solidified CoCrFeNiCux (x = 0,1,2) HEAs were investigated by glass fluxing technique. The maximum undercoolings were achieved by 365 K (0.21 TL), 381 K (0.23 TL) and 236 K (0.14 TL) for these alloy melts respectively. Once the Cu element was added into the CoCrFeNi HEA, the metastable phase separation took place and caused the formation of two obvious segregation zones when alloy undercooling exceeded a critical undercooling. The dendritic growth velocity increased with undercooling and declined gradually with the enhancement of Cu content. The microhardness of CoCrFeNi and CoCrFeNiCu HEAs increased with the undercooling owing to the refined microstructures, but that of CoCrFeNiCu2 HEA increased firstly and then declined with its undercooling because of phase separation.