Effect of Ru on Interfacial Re Segregation and Low-Cycle Fatigue Behavior of NiAlRe and NiAlReRu Model Superalloys

The effects of Ru on Re segregation and low-cycle fatigue (LCF) behavior were investigated in two model single-crystal superalloys, Ni-8.5Al-4Re and Ni-8.5Al-4Re-2Ru (wt.%). Microstructural morphology, elemental distribution, fatigue deformation behavior, and dislocation structures were systematically compared, and density functional theory (DFT) calculations were performed to examine the associated atomic and electronic effects. The results show that Re segregates at the γ′/γ interface in both alloys, whereas the addition of 2 wt.% Ru reduces the extent of interfacial Re segregation. The Gibbsian interfacial excess of Re decreases from 18.19 ± 1.75 to 11.42 ± 0.01 atom nm−2, while the maximum interfacial Re concentration ratio decreases from 1.36 ± 0.01 to 1.17 ± 0.02 after Ru addition. DFT calculations further show that Re increases the unstable stacking-fault energy of the γ′/γ interface by 10.34% relative to the unalloyed interface, whereas the corresponding increase is 5.05% in the Re–Ru co-doped system. Fatigue-deformed NiAlRe exhibits interfacial dislocation networks along the γ′/γ interfaces, whereas more extensive dislocation penetration into the γ′ precipitates is observed in NiAlReRu. At a strain amplitude of 0.6%, the Ru-containing alloy exhibits a lower cyclic stress response and more pronounced crack initiation and coalescence. These results show that Ru modifies the interfacial segregation behavior of Re and is associated with changes in the post-fatigue dislocation structures and high-temperature LCF response of the model superalloys.