Effect of high Co content doping on Na2SO4-induced hot corrosion behavior of aluminide coating on Mo-rich Ni3Al-based single-crystal superalloy at 900 °C

A combined approach of electroless plating and vapor phase aluminizing was employed to deposit aluminized coatings with varying Co contents onto the surface of an Mo-rich Ni 3 Al-based single-crystal superalloy. The hot corrosion behavior of these coatings was comparatively investigated during exposure to 100 wt.% Na 2 SO 4 molten salt at 900 °C, revealing the underlying mechanisms. The results demonstrated that Co doping significantly enhanced the coating’s resistance to sulfur-induced hot corrosion. This improvement progressed with increasing Co content. Furthermore, Co doping effectively suppressed the outward diffusion of Mo from the alloy substrate. Notably, when the deposited Co layer thickness reached 5 μm, Mo diffusion was effectively confined within the interdiffusion zone. During the hot corrosion stage, the majority of Mo remained suppressed within the substrate core. This substantial reduction in Mo outward diffusion significantly improved the coating’s resistance to sulfur-induced hot corrosion. For coatings containing higher Co levels, a multi-layered structure formed within the surface oxide scale during hot corrosion: the outermost layer consisted of CoAl 2 O 4 , followed by an intermediate layer of Al 2 O 3 , and an inner layer comprising a mixture of CoAl 2 O 4 and Al 2 O 3 phases. This multi-layered configuration contributed to maintaining the integrity of the oxide scale and effectively suppressed the progression of hot corrosion.