Study of High Temperature Oxidation Properties of Al2O3-SiO2 Ceramic Coatings on Nickel Superalloy

High-temperature ceramic coating on superalloy surface is a good method to improve high temperature performance of metal. Alumina-silica composite ceramic coatings were obtained on nickel superalloy substrates with the molar ratio of mullite by a sot-gel coating process according to hydrolytic condensation of organic alkoxide of aluminum and silicon elements. The oxidation behavior of the coatings was investigated by 1000 and 1200 degrees C heat treatment in the air for 20 h and by 20 times circular oxidation tests at 800 degrees C. The microstructure and states of coatings on the surface and section of nickel superalloy were observed by scanning electron microscope (SEM). The structural change of gels was analyzed by Fourier transform infrared (FT-IR) spectroscopy. The results show that there is an adhesive layer between the coating and the alloy substrate. Moreover, the disjuncting layer became blurred after long period of high temperature treatment. Alumina-silica composite ceramic coatings demonstrate excellent long-term performance at a high temperature of 1000 degrees C and repetitious thermal cyclic oxidation at 800 degrees C.