2015 年 33 巻 2 号 p. 30s-33s
Alumina (Al2O3) coatings by two types of plasma spraying method (APS: atmospheric plasma spraying and LPS: low pressure plasma spraying) were observed at the view point of coating structure in order to confirm superiority for electric isolation application. A breakdown voltage of dielectric layer is due to interlamellar gap continuous across Al2O3 coatings. The micron size evaluation of this gap was confirmed by macroscopic structure observation. The cross-sectional macroscopic structure was examined by copper electrolytic plating for visualization and by a scanning electron microscopy (SEM). Furthermore, dielectric volume resistivity was dominantly derived from microscopic structure and crystallinity of the coatings. The cross-sectional microscopic structure of the coatings was observed by a field emission SEM (FE-SEM). The crystallographic analyses were performed by electron back scatter diffraction (EBSD). As an evaluation result, there are no differences in macroscopic structures with gap of coatings between two spraying methods. The Al2O3 particles partially melted in spraying and made cracks in solidifying. The gap was derived from the cracking of molten particles and also exhibited the same structures between two spraying methods. Coating electric properties had no significant differences between two spraying methods. In this study, the factors which so significant differences were not observed in electric properties each spraying methods are investigated macroscopically and microscopically.
