Anomalous microstructure and excellent mechanical behaviors of (CoCrFeNi)6-x-yCrxAly high-entropy alloy induced by Cr and Al addition

Abstract

The (CoCrFeNi)6-x-yCrxAly (x = 0.5, y = 0; x = 1, y = 0; and x = 1, y = 1) high-entropy alloys were prepared, and the microstructure and mechanical behaviors were investigated. The crystal structure changed from a sole face-centered-cubic (FCC) structure to a dual-phase structure of FCC plus body-centered-cubic (BCC) structure with the increasing of Cr content. By controlling the addition of Al and Cr elements, the crystalline structure changed to a BCC structure, which was composed of two ordered BCC phase. One is (Al, Ni)-enriched, and the other is (Co, Fe, Cr)-enriched. The increment of the BCC/B2 phase could significantly enhance the hardness and yield strength with a slight sacrifice to ductility. The nanoindentation tests showed that with the increasing of the Al and Cr content, the nano-hardness increased from 4.58 GPa to 8.95 GPa, and the elastic modulus increased from 200.83 GPa to 233.76 GPa, respectively. Based on the nanoindentation results, the H/Er and H3/Er2 values were calculated, which could be used to estimate the wear resistance. Both the H/Er ratio and H3/Er2 ratio showed an increase trend with the addition of Cr and Al elements, which demonstrated that the anti-wear ability was enhanced. The compression tests indicated that the (CoCrFeNi)4Cr1Al1 alloy demonstrated excellent comprehensive compression properties, whose yield strength and fracture strain is 1653 MPa and 29.5%, respectively. Furthermore, the strengthening mechanism has been discussed. In comparison with the solid solution strengthening, the second phase strengthening is dominant.