Carbide precipitation strengthening in fine-grained carbon-doped FeCoCrNiMn high entropy alloy

Nano-sized carbides in carbon-doped high entropy alloys (HEAs) can induce remarkable precipitation strengthening, but the precipitation behavior and its effects on mechanical properties has not been clarified. In this study, a heavy-carbon doped equiatomic FeCoCrNiMn HEA with 1.3 at.% C addition (FeCoCrNiMn-1.3C) was prepared to provide an insight into the effect of carbides precipitation on the strength of the HEA. The results showed that FeCoCrNiMn-1.3C HEA exhibited a single FCC structure after homogenization treatment at 1220 °C for 6 h and the subsequent severe cold rolling (SCR) with 95% reduction. It was found that nano-sized M₂₃C₆ carbides can precipitate and exist stably in the SCRed FeCoCrNiMn-1.3C HEA during annealing at 700–1000 °C. These nano-sized M₂₃C₆ precipitations can substantially inhibit the recrystallized grain growth of FCC matrix in the SCRed FeCoCrNiMn HEA during annealing. The average grain size of the SCRed HEA can be maintained at 2.4 μm even after annealing at 1000 °C for 1 h due to the M₂₃C₆ precipitations inhibition on grain growth. The yield strength of ∼1040 MPa with total elongation of ∼12% has been achieved in FeCoCrNiMn-1.3C HEA after annealing at 700 °C for 1 h. Grain refinement and precipitation strengthening are the two major strengthening mechanisms of the present annealed FeCoCrNiMn-1.3C HEAs.