Study on High Temperature Properties of Yttrium-Modified Aluminide Coating on K444 Alloy by Chemical Vapor Deposition

This work aims to explore a method of improving the high-temperature oxidation resistance and thermal corrosion resistance of a hollow blade of gas turbine. The yttrium-modified aluminide coating was prepared on the surface of nickel-based superalloy K444 by chemical vapor deposition (CVD). The microstructure, high temperature oxidation resistance, and thermal corrosion resistance of the modified aluminide coating deposited at 950 °C, 1000 °C, and 1050 °C were compared. The microstructure and morphology of the coatings were observed and analyzed by XRD, SEM, and EDS. The results showed that adding yttrium and changing the deposition temperature had no effect on the double-layer structure (outer layer and diffusion layer) of the coating. Compared with adding yttrium, the deposition temperature had a greater effect on the coating thickness. When the deposition temperature was 1050 °C and the deposition time was 2 h, the thickness of the yttrium-modified aluminide coating increased by 33% compared to that of a single aluminide coating. The high temperature oxidation resistance and thermal corrosion resistance of the three groups of yttrium-modified aluminide coatings are better than that of the single aluminide coating. The resistance to high temperature oxidation and hot corrosion of the yttrium-modified aluminide coating deposited at 1050 °C was better than that of yttrium-modified aluminide coating deposited at 1000 °C, and both were better than that of the modified coating deposited at 950 °C. The higher the deposition temperature, the higher the yttrium content of the coating, the faster the film-forming speed of α-Al2O3, and the better the high temperature oxidation resistance and thermal corrosion resistance of the coating.