Microstructure and Compressive Deformation Behavior of As-Cast CrFeCoNiCux High Entropy Alloys

In this work, the microstructure, compressive strength, strain rate sensitivity and deformation behaviors of CrFeCoNi (denoted as Cu0) and CrFeCoNiCu0.6 (denoted as Cu0.6) alloys were thoroughly investigated. Experimental results revealed that in the case of Cu addition, a net-work Cu-rich face-centered cubic phase (FCC2) was formed within the face-centered cubic matrix (FCC1). Compared with the Cu-free alloy, the grain size of the Cu-containing alloy was significantly refined, and the lattices of its component phases expanded. Compared with Cu-free HEA, the compressive yield strength of Cu0.6 alloy was almost double, and had higher positive strain sensitivity parameter (m). The work-hardening rate of the two alloys had the same changing trend, in which first dropping sharply, then remaining stable, and finally gradual increasing. Except for grain breakage and dislocation entanglement, hindrance of FCC1/FCC2 interface to dislocation slip contributed to the gradual increase of work hardening rate of Cu0.6 alloy. Under the action of compression stress, the long-strip grains of both alloys would rotate perpendicular to the compression axis and are accompanied by necking and tearing. With the increase of compression strain, the high-density dislocation would be rearranged to form a dislocation wall, and then transformed into a sub-grain. In addition, the high strain rate led to the formation of a network dislocation structure in the deformed FCC2 phase.