Comprehensive study on the microstructure evolution and oxidation resistance performance of NiCoCrAlYTa coating during isothermal oxidation at High temperature

The microstructural evolution and high temperature oxidation resistance performance of NiCoCrAlYTa coating were investigated via isothermal oxidation at 1100 degrees C and 1150 degrees C for up to 200 h. The results reveal that the microstructure of oxides scale formed at higher temperature gradually evolve from a dense alumina layer to a mixed oxide layer, consisting of alpha-Al2O3 and considerable amount of NiAl2O4 spinel, NiO as well as abundant amount of (Y, Ta)-enriched oxides, which not only caused the formation of defects, such as voids and cracks, but also developed a rumpling of coating surface, accelerating the aggregation and growth of cracks. And serious internal oxidation was also detected as the oxidation time increased, which was discussed and explained from the aspect of interdiffusion behavior. At high temperature of 1100 degrees C and 1150 degrees C, the oxidation kinetics curve deviated from parabolic law, indicating the oxidation resistance property of NiCoCrAlYTa coating compromised under these severe conditions. Based on the result of calculated diffusion activation energy, the failure mechanism of NiCoCrAlYTa coating is largely dependent on the exposure temperature. During the growth of oxides scale, the external diffusion of cations is the mainly process, accompanied with the internal diffusion of oxygen to a certain degree. The results could provide comprehensive understanding of the microstructural evolution during oxidation, which was essential for controlling oxides scale growth and improving the durability of NiCoCrAlYTa coating.