800oC-stable D022 superlattice in a NiCrFe-based medium entropy alloy

The metastable-stable transition and rapid coarsening of metastable D022 phase remains its Achilles hell, restricting the application of D022-strengthened alloys at service temperatures higher than 650°C. Hence, it is crucial to improve thermal stability of D022 phase. In this work, we report an 800°C-stable D022-Ni3(W0.24Ti0.38Ta0.19Nb0.19) superlattice in the Ni58Cr23Fe10W5Ti2Ta1Nb1 MEA. Experimental results and theoretical analysis showed that the exceptional thermal stability is due to Nb-sublattice occupying elements, low diffusivity of W, and extremely small lattice misfit between the D022 phase and FCC matrix. These findings shed lights on developing high-performance D022-hardened alloys capable of operating at temperatures above 650°C.