Microstructure and mechanical behaviors of CoFeNiMnTi x Al 1-x high entropy alloys

In this study, the microstructure and mechanical properties of CoFeNiMnTixAl1-x (where the molar ratio (x) is 0, 0.1, 0.3, 0.5, 0.8, and 1) high entropy alloys (HEAs) were investigated. The body-centered cubic (BCC) phase, face-centered cubic (FCC) phase, and Laves phase were found in the alloy system. With an increase in the Ti content and a decrease in the Al content, the structure changes of the alloys from BCC to BCC + FCC to BCC + FCC + Laves, and then to Laves + FCC phases. The FCC phase is located at the BCC grain boundary. The CoFeNiMnTi0.5Al0.5 HEA with a BCC + FCC duplex phase structure shows the optimal performance of both strength and ductility. The yield strength, fracture strength, and fracture strain can reach 1052.8 MPa, 2402.4 MPa, and 20.5%, respectively. The hardness reaches HV518.7. Nanoindentation experiments show that the BCC phase is harder than the FCC phase in the CoFeNiMnTi0.5Al0.5 HEA. Furthermore, the deformation behaviors of the FCC phase and BCC phase are studied by measuring the first pop-in behavior.