Enhanced strength-ductility balance of the (CoCrFeNiMn)95.2Al3.2Ti1.6 high-entropy alloy by co-precipitation of the B2 and sigma phases

Abstract

The present work investigated the effect of the co-precipitation of the B2 and σ phases on the mechanical properties of the (CoCrFeNiMn)95.2Al3.2Ti1.6 high entropy alloy subjected to two-step annealing. The single-step annealed sample at 900 °C only showed B2 precipitates. Further annealing at 650 and 750 °C led to the co-precipitation of σ and B2 particles. The sizes and fractions of σ and B2 particles increased with increasing annealing temperature. The sample subjected to the second annealing at 750 °C, with large sizes and fractions of co-precipitated σ and B2 particles, exhibited high strength with maintaining moderate ductility (YS: 561 MPa, UTS: 1005 MPa, TE: 26%). The superior mechanical properties of the sample subjected to the second annealing at 750 °C could be owing to the co-precipitation hardening, back stress strengthening, joint activation of dislocation plasticity and deformation twinning. The present work offers a novel microstructure design to optimize the strength–ductility balance of high-entropy alloys via the co-precipitation of σ and B2 particles.