MCrAlY coatings and thermal barrier coatings (TBC) are commonly used in gas turbines to prolong the life of structural parts. The atmospheric plasma spray (APS) process yields coatings with a typical splat-on-splat structure which oxidizes at intersplat boundaries during high-temperature exposure. A study was performed to establish the influence of intersplat oxidation on Al depletion. It was found that the β-depletion based life may be overestimated by a factor of 1.8–18 if intersplat oxidation is not considered. Two different mechanisms of intersplat oxidation were observed: At high temperature (1050 °C), a fraction of the intersplat boundaries remained in contact with the coating surface and oxidized with the same kinetics as the surface oxides. At lower temperature (900 °C), intersplat oxidation occurred by considerable slower growth rates than surface oxidation. The mechanisms behind intersplat oxide growth was further studied by O diffusion calculations.

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