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

The metastable-stable transition and rapid coarsening of metastable D0(22) phase remains its Achilles hell, restricting the application of D0(22)-strengthened alloys at service temperatures higher than 650(degrees)C. Hence, it is crucial to improve thermal stability of D022 phase. In this work, we report an 800(degrees)C-stable D0(22)-Ni-3(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 D0(22) phase and FCC matrix. These findings shed lights on developing high-performance D0(22)-hardened alloys capable of operating at temperatures above 650(degrees)C. GRAPHICAL ABSTRACT