MCrAIY overlay coatings have been widely used in industrial gas turbines to provide good oxidation resistance,corrosion resistance and preserve good mechanical properties of nickel-based superalloys at elevated temperature [1].Generally,MCrAIY coatings are produced by vacuum plasma spraying (VPS) technique.However,the VPS technique is expensive in use,interests have been paid to find a technological altemative [2].Recently,a new thermal spraying process—high-velocity oxygen fuel (HVOF)—was developed and used to produce MCrAIY coatings.HVOF coatings have very low porosity,high hardness,good wear resistance and a strong ability to resist high-temperature corrosion [3].However few researches have been done about the failure mechanisms of the coating prepared by HVOF process.