Dynamic deformation behavior and microstructure evolution of CoCrNiMox medium entropy alloys

Abstract In this work, the dynamic response at a similar high strain rate of a series of Mo-doped CoCrNi medium entropy alloys, i.e., CoCrNiMox (x = 0, 0.1, 0.2), was investigated via a split Hopkinson pressure bar (SHPB). We found that with the Mo amount increasing from 0 to 0.2, the yield strength nearly doubles, from ∼450 to ∼800 MPa, under such a high strain rate. Detailed microscopy investigations revealed that the strengthening from solid solution and precipitation, together with the high work hardening rate via micro-banding and nano-twinning/stacking faulting, contribute to strength increment and better work hardening ability. After dynamic compression, the sample with the more Mo was found to have the higher dislocation density and the more frequent nanotwin/stacking fault events. This suggests that Mo plays a critical role in both dislocation accumulation (planar slip) and dislocation dissociation (stacking fault energy) during the ultra-fast plastic flow, which endows the Mo0.2 alloy a potential for application in impact protection.