Radio‐Frequency Plasma Spraying of Ceramics

This study was aimed at developing a novel spraying process using a radio‐frequency (rf) plasma. Experiments of Al 2 O 3 and ZrO 2 –8 wt% Y 2 O 3 spraying showed that the initial powder size was the most important parameter for depositing dense coatings. The optimum powder sizes of Al 2 O 3 and ZrO 2 –8 wt% Y 2 O 3 were considered to be around 100 and 80 μm, respectively. The use of such large‐size powders compared with those used by conventional dc plasma spraying made it possible to deposit adherent ceramics coatings of 150 to 300 μm on as‐rolled SS304 substrates. It was also shown that low particle velocity of about 10 m/s, which is peculiar to rf plasma spraying, was sufficient for particle deformation, though it imposed a severe limitation on the substrate position. These experimental results have proved that rf plasma spraying is an effective process and must be a strong candidate to open new fields of spraying applications.