Structural and chemical disorder enhance point defect diffusion and atomic transport in Ni3Al-based γ′ phase

The ordered L1(2) gamma' Ni3Al intermetallic inclusions are routinely used as strengthening constituents in Ni-based superalloys and recent high-entropy alloys. As there are different metallic elements relative to the alloy matrix, the composition of gamma' phase inclusions usually suffers some variations. In this work, we studied the elemental partition and its influence on atomic transport properties in a model (NiCo)(3)Al gamma' phase with chemical and structural disorder. Combining the Monte Carlo and molecular static techniques, we first determined the elemental distribution in such compositionally-complexed gamma' phase. The results suggest that Co tends to segregate, which profoundly influences defect energetics and diffusion properties. By modeling thermally activated diffusion by molecular dynamics, we found that chemical disorder induced by Co can enhance vacancy diffusion while significantly suppress diffusion via interstitial atom migration, as compared to the stoichiometric gamma' Ni3Al. We further reveal that these observations are closely related to the defect energetics in these systems. Our results explain the effects of disorder, long-and short-range orders on the diffusion properties in multicomponent intermetallic alloys, which helps to understand the stability and, thus, gamma'-phase-assisted strengthening at different conditions including annealing and irradiation. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study focuses on the effect of elemental distribution in intermetallic compounds and the influence of chemical disorder induced by cobalt on diffusion properties, revealing that cobalt segregation affects defect energetics and diffusion properties.