Abstract: Engineering alloys with complex components are typically subjected to localized chemical fluctuations, especially at interfaces. However, how such chemical heterogeneity would influence interfacial dynamics under external stimulations remains largely unclear. Here, using state-of-the-art electron microscopy and density functional theory calculations, we reveal the sequential formation of stacking faults (SFs), hexagonal close-packed (HCP) structure, and topologically close-packed (TCP) phase induced by the chemical heterogeneity at γ/γ’ interfaces in Ni-based single crystal superalloys. Constituent elements like Re, Mo, and Cr exhibit strong co-segregation tendencies at (111)_γ/γ’ interfaces, leading to the preferential nucleation of interfacial SFs and their subsequent transformation into HCP structure. Solute-segregation mediated solute enrichment and ordering within such interfacial HCP structure are shown to template the nucleation of TCP phases via the shuffle of certain atoms. These findings unveil the critical role of interfacial chemical fluctuations on structural degradation of Ni-based superalloys, offering insight into the design of novel superalloys towards superior properties.

Key words: Interfacial chemical fluctuation, Planar defects, Topologically close-packed phase, Solid-state phase transformations, Ni-based superalloys