セラミック溶射皮膜の微細構造研究

抄録

Ceramic coatings of MgO⋅Al₂O₃ and ZrO₂ (8wt% Y₂O₃) sprayed by water plasma were examined. They showed rough texture with especially large grains, large pores of over 20μm and layered structure resulting from excessive fusion of powder materials. On the other hand, ceramic coatings of the same chemical composition sprayed by gas plasma had relatively homogeneous texture with grains of about 30μm and pores of 5-10μm. Results of thermal spalling tests showed that it was necessary to have a microstructure with fine grains and fine pores distributed homogeneously in order to decrease the exfoliation due to temperature change. Two kinds of powders in the system Al₂O₃-Cr₂O₃ were applied to gas plasma spraying in order to study the effect of powder materials on the properties of sprayed coatings. The sprayed coating with an electrofused powder was a solid solution, while the sprayed coating with a mixed powder of Al₂O₃ and Cr₂O₃ consisted of layered structure of γ-Al₂O₃ and Cr₂O₃ crystals. The solid solution coating seemed to be more resistant to exfoliation, since AE counts of the coating with the electrofused powder at the temperature change were one tenth of those with the mixed powder.