An Al plus Y coating process for improvement of the high-temperature oxidation resistance of a TiAl alloy

An Al + Y codeposition by a single EB-PVD process has been developed to imp rove the high-temperature oxidation resistance of a TiAl alloy. The Al + Y codeposited TiAl alloy with various ratios of Al and Y evaporation sources was evaluated by isothermal and cyclic-oxidation tests. The coating layer h as a composition gradient because of the difference in vapor pressure betwe en Y and Al. The oxidation resistance can be extensively improved by the fo rmation of an Al + Y codeposition layer and it depends on the ratio of the source material of Al and Y. The best oxidation resistance was obtained fro m the Al + Y codeposited TiAl alloy with a ratio of Al:2Y. With the proper ratio of Al. Y, the Al + Y codeposition coating forms Two layers of the oxi des during high-temperature oxidation + the outer (Y, Al) O layer and the i nner Al2O3 layer, containing small amounts of Y oxide. These oxide layers, which have a fine grain size, act as a diffusion barrier, thus suppressing the rate of inward diffusion of O and may readily relieve thermal stresses.