Mechanical properties and fracture mechanism of as-cast MnFeCoCuNi high-entropy alloys

MnFeCoCuNix high-entropy alloys (HEAs) with different Ni contents were fabricated by vacuum induction melting. XRD and SEM−EDS were used to analyze the phase constitution and structure, and the tensile properties of the samples were determined using a universal tensile tester. The results show that the HEAs consist of a dual-phase structure, in which FCC1 phase is rich in Fe and Co, while the FCC2 phase has high contents of Cu and Mn. As Ni content increases, the segregation of Cu decreases, accompanied by the decrease of FCC2 phase. Moreover, the tensile strength of the HEAs increases first and then decreases, and the elongation increases slightly. This is attributed to the combined effect of interface strengthening and solid solution strengthening. The in-situ stretched MnFeCoCuNi0.5 alloy shows obvious neck shrinkage during the tensile fracture process. In the initial deformation stage, the slip lines show different morphologies in the dual-phase structure. However, in the later stage, the surface slip lines become longer and denser due to the redistribution of atoms and the re-separation of the dissolved phase.