Growth stress and interdiffusion analysis of NiCoCrAlYTa coating during oxidation

Abstract

The NiCoCrAlYTa coating deposited on Ni-based superalloy using arc ion plating (AIP) technology was subjected to isothermal oxidation in air at 1050°C for up to 200 h. The microstructure, oxides scale thickness, growth stress and interface diffusion behaviour were characterized by using scanning electron microscopy, X-ray diffraction, electron probe micro-analyser and photo-stimulated luminescence piezo-spectroscopy. The results revealed that the microstructure of oxides scale was predominantly composed of α-Al₂O₃ with (Y, Ta)-rich oxides and Cr₂O₃ irregularly distributed during the oxidation process. The oxides scale thickness of NiCoCrAlYTa coating conformed to parabolic law, which indicated the coating had good oxidation resistance. Also, the relationship between the thickness and growth stress, as well as the oxidation time, was studied based on the Clark oxidation theory and Wagner oxidation model, developing a methodology to measure the high-temperature stress in NiCoCrAlYTa coating. The theoretical calculation value of the stress was basically consistent with the value of the experiment, which could effectively predict the growth stress in the coating and help understand the failure mechanism of NiCoCrAlYTa coating during the service life. In the oxidation process, the interdiffusion behaviour occurred at the interface between the oxides scale and the NiCoCrAlYTa coating was also discussed. The diffusion coefficient of typical elements was calculated by using Boltzmann–Matano method, which was helpful to analyse the inner oxidation of the NiCoCrAlYTa coating, providing in-depth understanding of the oxidation behaviour.