Effect of Mo-doping on the stability of D0₂₂ superlattice and mechanical properties in the Ni_2.1CoCrFeNb_0.2 high entropy alloy

High entropy alloys (HEAs) with D0₂₂ superlattice have shown excellent yield strength. However, long-time annealing leads to the decrease of strength due to the coarsening of D0₂₂ superlattice. Therefore, stabilizing the D0₂₂ phase of HEAs is of critical importance. Here, we report that a minor addition of Mo significantly enhances the phase stability of D0₂₂ phase and mechanical performance of Ni_2.1CoCrFeNb_0.2 HEAs. Experimental results show that the Mo-doping slows down the coarsening of D0₂₂ phase significantly by decreasing the diffusivity and reducing the lattice misfit between precipitates and matrix. Due to the enhanced coarsening resistance of D0₂₂ phase, the Mo-doped Ni_2.1CoCrFeNb_0.2 HEA shows good strength and ductility after long-term aging. These insights provide some guidelines for the design of precipitation-hardened alloys for high-temperature application.