Effects of Sc addition on microstructure, phase evolution and mechanical properties of Al_0.2CoCrFeNi high-entropy alloys

l(0.2)CoCrFeNiSc(x) (x=0, 0.1, 0.2 and 0.3, molar fraction) alloys were prepared by arc melting. The effects of Sc addition on the microstructure, phase evolution and mechanical properties of Al0.2CoCrFeNiScx alloys were investigated. The results showed that Sc could refine grain size, change phase type and improve mechanical properties. The grain size of Al0.2CoCrFeNiSc0.3 alloy (8.5 mu m) was reduced by approximately 50.6% compared to that of Al0.2CoCrFeNiSc0.1 alloy (17.2 mu m). The crystal structure evolved from a single FCC phase to a mixed phase including two types of FCC phases and one type of BCC phase. The FCC phase mainly appeared in the regions of (Co, Cr, Fe)- rich dendrites and (Ni, Sc)-rich interdendrites; while the BCC phase was mainly located in the region of (Al, Ni)-rich interdendrites. The yield strength increased from 167 to 717 MPa as the x value in Al0.2CoCrFeNiScx alloy increased from 0 to 0.3, improved by 329.3%, which could be attributed to grain size strengthening, solid solution strengthening and phase evolution.