Two types of coatings, NiCrAlY and NiCrAlY/YSZ, were fabricated on the surface of M247 alloy by the atmospheric plasma spraying (APS) technique. Under pure Na₂SO₄ and 25 wt.% NaCl-containing mixed salt deposits at 900 °C in air, the M247 alloy underwent rapid catastrophic corrosion. The non-protective corrosion products formed on the surface included NiO and (Ni,Co)Cr₂O₄ spinel. The hot corrosion of M247 under the pure Na₂SO₄ salt deposit followed a basic fluxing mechanism, whereas under the NaCl-containing mixed salt deposit, it was dominated by an active oxidation mechanism. During hot corrosion, the NiCrAlY coating developed a continuous, dense, and highly protective α-Al₂O₃ oxide scale on its surface, endowing it with superior hot corrosion resistance. The thermal barrier coating of NiCrAlY/YSZ exhibited the best hot corrosion resistance, attributed to the physical barrier and thermal barrier effects of the outer YSZ ceramic layer.

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.