Effects of heat treatment on the precipitation behaviors and mechanical properties of Nb-doped CrMnFeCoNi0.8 high-entropy alloy

In this work, the CrMnFeCoNi0·8Nb0.2 high-entropy alloys (HEAs) were fabricated through vacuum induction melting and subsequently annealed at various temperatures (namely, 900 °C, 1000 °C, and 1100 °C). The microstructure and mechanical properties of the HEAs following heat treatment were investigated systematically. It reveals that the annealed alloys demonstrate the coexistence of the face-centered cubic (FCC) matrix phases and Laves phases, wherein partial dissolution of primary NbCo2 phases into the matrix while the remaining part precipitation as secondary phases. The alloy annealed at 1000 °C exhibits a ductility of 13.2%, along with high yield strength of 497.8 MPa, ultimate tensile strength of 851.1 MPa and hardness of 393.9 HV. The high strength of the alloy primarily originates from the hetero-deformation induced (HDI) strengthening of the eutectic-like structure, while additional strengthening is provided by precipitation strengthening caused by nano-sized second precipitates and solution strengthening.