Trace B doping Fe50Mn30Co10Cr10 high entropy alloy: Mechanical response and multi-microstructure evolution under TWIP and TRIP effects

Face-centered cubic (FCC) high entropy alloy has attracted extensive attention because of its excellent mechanical response, while its poor strength limits its application in practical engineering. In this work, the Fe50Mn30Co10Cr10 alloy doped with 30 ppm B atoms and proper thermo-mechanical processing (cold rolling and annealing) has achieved excellent synthetic strength and plasticity. It was found that the grain refinement strengthening introduced by B doping and the strong dislocation strengthening of inhomogeneity structure produced by the annealing treatment contribute to enhanced yield strength. The multiple structure evolution during the deformation process contribute to the excellent ductility. With the increase of tensile strain, dislocations, FCC deformation twins, strain-induced close packed hexagonal structure (HCP) phase, HCP deformation twins and reverse FCC phase appear successively, implying an interesting mechanism that the FCC and HCP phases bear plastic deformation by twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects successively. FCC twinning, FCC-*HCP phase transformation, HCP twinning, HCP-*FCC reverse transformation occurred successively, which simultaneously leads to the high plasticity of the alloy. Interstitial atoms doping combined with the TWIP and TRIP effects can lead to the overall improvement of the yield strength and plasticity of the alloy, which provides a feasible way for the subsequent design of high-strength plastic alloys.