High-Temperature Oxidation Behavior of a Silico-Aluminized MCrAlY Coating on a Ni-Based Superalloy

In this research, silico-aluminide diffusion coating was applied on a conventional NiCoCrAlY coating that was deposited on Hastelloy-X superalloy via the high-velocity oxy-fuel (HVOF) thermal spraying technique. The slurry method was utilized as the diffusion coating method. Diffusion heat treatment was carried out at 1050 degrees C. High-temperature oxidation behavior of NiCoCrAlY/silico-aluminide coated samples was studied at 1000 degrees C and compared with those of conventional NiCoCrAlY coatings. The coatings were explored using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis before and after oxidation testing. Both coatings followed parabolic kinetics. The silico-aluminide overlay coating outperformed the NiCoCrAlY coating with respective parabolic rate constants of 0.0958 and 0.1702 mu m(2)/h. After 150 h of oxidation, the silico-aluminized overlay coating maintained a single layer of alumina, while a double-layered oxide consisting of spinel and aluminum oxide was observed in the case of conventional NiCoCrAlY coating, reflecting higher stability of the NiCoCrAlY/silico-aluminized coating.