TRIP-TWIP effect in deformation mechanisms of Co–Cr–Ni medium entropy via molecular dynamics simulations

Recently, Co–Cr–Ni medium-entropy alloys (MEAs) have garnered significant attention in the materials field owing to exceptional properties. However, the various mechanisms of transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects with variation of chemical compositions, strain rates, temperature and grain size in polycrystalline Co–Cr–Ni MEAs remains challenging. By utilizing molecular dynamics simulations, the uniaxial tensile deformation of polycrystalline Co–Cr–Ni MEAs, including equiatomic CoCrNi, and non-equiatomic Co10(CrNi)90, Cr10(CoNi)90 and Ni10(CoCr)90, has been investigated. The influence of strain rates and deformation temperatures on the mechanical properties and deformation mechanisms of CoCrNi MEA has also been explored under uniaxial tensile loading. Further, dislocation multiplication, slip motion, microstructure evolution, and their interplay with tensile deformation under different conditions have also been studied. Additionally, the relationship between different grain sizes and the flow stress of polycrystalline CoCrNi MEA has also been discussed. The findings reveal that Co10(CrNi)90 MEA exhibits highest yield stress, Young's modulus, and flow stress. While CoCrNi MEA and Cr10(CoNi)90 MEA with equiatomic ratios display similar mechanical properties, Ni10(CoCr)90 MEA demonstrates superior ductility owing to the strong TWIP and TRIP effects. Besides, strain rate, deformation temperature, and grain size all have significant impacts on the deformation mechanisms of polycrystalline CoCrNi MEA.