Plastic deformation mechanism of CoCrxNi medium entropy alloys

The mechanical properties of multi-principal element alloys show a big difference with or without Cr additions. In this work, the roles of Cr on the mechanical properties, especially the plastic deformation mechanism of CoCr_xNi alloys are systematically investigated. The results indicate the strength and ductility of CoCr_xNi alloys are improved simultaneously with the increase of Cr. Deformation twin bands are significantly thinner. The first principle calculations indicate the average SFE is lower and energetic fluctuation is larger for CoCrNi than that of CoNi, which may contribute to the more nucleation of nano-twins with the increase of Cr. Meanwhile, a transition of dislocation pattern from dislocation cells to slip bands is observed. Not only the formation of nano-twins, but also the dislocation patterns are the reason for the excellent plasticity and work hardening ability of CoCrNi alloy.