Effect of Mo-doping on the stability of D022 superlattice and mechanical properties in the Ni2.1CoCrFeNb0.2 high entropy alloy

Abstract

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 Ni2.1CoCrFeNb0.2 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 Ni2.1CoCrFeNb0.2 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.