Crack-resistant sigma/FCC interfaces in the Fe40Mn40Co10Cr10 high entropy alloy with the dispersed sigma-phase

Abstract

We report the role of morphology and size of the a-phase on mechanical properties of the Fe40Mn40Co10Cr10 non-equiatomic high entropy alloy. The dispersed and fine sigma-precipitates formed after cold-rolling and annealing at 700 degrees C for 1 h lead to an increase in strength without severe ductility loss compared to the material without the sigma-phase. However, the coarsened and connected sigma-phase formed after prolonged annealing at 700 degrees C for 100 h results in early failure due to the activation of microcracks along sigma/sigma interfaces. The sigma/FCC interface could act as strong obstacles for dislocation motion and could effectively relieve the stress concentration by activating deformation twins or dislocations. The sigma/FCC interfaces are excellent in terms of hardening, accommodation of plastic deformation, and stress relaxation leading to the observed crack resistance. Therefore, we suggest that increasing sigma/FCC interfaces by controlling size and dispersion of the sigma-phase is essential to develop HEAs with an excellent strength-ductility combination and damage tolerance.