Influence of heat exposure time on isothermal degradation of plasma sprayed CoNiCrAlY coatings

In this work, the thermal degradation behavior of selected CoNiCrAlY coatings has been studied. Emphasis was placed upon the change of oxygen content, porosity, surface roughness, and oxidation behavior. The results show that the isothermal degradation of coatings was considerably influenced by the heat exposure time and powder particle distribution. The values of oxygen content, surface roughness, and TGO scales converge sharply into the stable extremes at the initial stage of heat exposure. The particle size has an effect on the oxygen content in as-sprayed coatings. After heat exposure, the difference of the oxygen content on coating deposited using between the smaller and larger particle was decreased. The cross-sectional porosity decreased at Stage I_P, increased at Stage II_P, and then decreased again. These could be due to the sintering effect at Stage I_P. The surface roughness decreased up to Stage I_R, but over Stage I_R, surface roughness was kept in relatively fixed value or increased slightly. The TGO thickness growth rate and parabolic oxidation rate constant are influenced by the surface roughness of coatings.