Deposition of Silicon-Enriched Nickel Aluminide Coatings on Internally Cooled Airfoils

摘要

We have shown that formation ofrnnickel aluminide coatings enriched with silicon is possible when using HC1 gas activation. The aluminum and silicon donating materials are provided as solids, which do not melt during the high-temperature diffusion process. By adjusting the Al:Si donator ratio, it is possible to deposit Ni-Al-Si coatings in a single-step process. A two-step process involving first aluminizing and then siliconizing leads to a depletion of aluminum and replacement by nickel silicides. Internal coating of complex structures (e.g., cooling channels of airfoils) is possible in principle. However, coating thickness and silicon content are significantly lower compared to external surfaces. Silicon-enriched layers normally lead to superior surface protection against hot corrosion when compared to simple nickel aluminide diffusion coatings. Further investiga-rntions will focus on optimization of internal coating by varying pressure parameters and donator mixtures.