Strengthening and deformation mechanism of high-strength CrMnFeCoNi high entropy alloy prepared by powder metallurgy

Multiphase CrMnFeCoNi high-entropy alloys (HEAs) were prepared by a powder metallurgy process combining mechanical alloying (MA) and vacuum hot-pressing sintering (HPS). The single-phase face-centered cubic (FCC) HEA powder prepared by MA was sintered into a bulk HEA specimen containing FCC phase matrix along with precipitated M23C6 phase and nanoscale σ phase particles. When the sintering temperature was 1223 K, the ultimate strength reaches 1300 ± 11.6 MPa, and the elongation exceeds 4% ± 0.6%. Microstructural characterization reveals that the formation of nanoscale particles and deformation twins play critical roles in improving the strain hardening (SH) ability. Prolonging the MA time promoted the formation of the precipitated phase and enhanced the SH ability by increasing the number of precipitated particles. The SH capacity increases significantly with increasing sintering temperature, which is attributed to a significant enhancement in the twinning capacity due to grain growth and the reduced number of σ phase particles. Through systematic studies, the planar glide of dislocations was found to be the main mode of deformation, while deformation twinning appeared as an auxiliary deformation mode when the twinning stress was reached. Although the formation of precipitates leads to grain boundary and precipitation strengthening effects, crack initiation is more prominent owing to increased grain boundary brittleness around the precipitated M23C6 phase. The prominence of crack initiation is a contradiction that must be reconciled with regard to precipitation strengthening. This work serves as a useful reference for the preparation of high-strength HEA parts by powder metallurgy.