Behavior of Ceramic Thermal Spray Coatings under Plasma Exposure

This study investigates plasma erosion mechanisms in alumina and yttria coatings produced by air plasma spraying. Plasma exposure tests were conducted in ICP etchers using CF₄, Ar, and O₂ as process gases. Etching rates were calculated based on height differences between masked and unmasked areas and coating cross-sections, surface morphologies, and phase distributions were analyzed. In the Al₂O₃ layers, erosion increased with increasing CF₄ concentration and fluoridation of the coating surface was confirmed, suggesting that chemical erosion is the dominant mechanism. Although fluoridation occurred on Y₂O₃ surfaces as well, the amount of erosion in CF₄ was the same as in the Ar environment. It is thus assumed that the fluoride formed on Y₂O₃ surfaces is very stable and that physical erosion due to ion sputtering is the dominant mechanism.