Microstructures and mechanical properties of (CoCrFeMnNi)100-xMox high entropy alloy films

The effects of Mo addition on the microstructures and mechanical properties of CoCrFeMnNi high entropy alloy films (HEAFs) were studied in this work. To achieve this, a series of (CoCrFeMnNi)100-xMox HEAFs was prepared by magnetron co-sputtering. The films were FCC without Mo addition and composed of FCC and HCP structures with minor Mo addition. With the further increase in Mo content, the films transformed to an amorphous structure. Nanoindentation revealed an initial decrease in hardness and then increase with the increasing Mo content. While the initial decrease in hardness could be attributed to the detwinning-induced softening for films with small twin spacing as observed by TEM after micropillar compression, the subsequent increase could be attributed to solid solution strengthening and formation of nanotwins with larger twin spacing and no detwinning observed after compression. Using scratch tests, the Mo-doped HEAFs exhibited a high hardness, good wear resistance and low coefficient of friction. The results of micropillar compression tests showed the increasing compressive yield strength and the decreasing fracture strain with the increasing Mo content. When x = 4.9, the film revealed the optimum mechanical properties with fracture strength of 6.51 GPa and little reduction in ductility.