Production of High Quality Coatings by Thermal Plasma Processing

By using the plasma spray gun which has high stability, the thermal plasma spraying of refractory materials (i.e. Al_2O_3,TiC and ZrC) at pressure of 200 and 760 Torr is studied. The spray gun consists of the local wall constricted type d. c. plasma jet generator and the feed ring to inject coating materials into plasma jet. To characterize the sprayed coatings, SEM and X-ray diffractometer are used. According to the present results, it is found that sprayed coatings at pressure of 200 Torr are denser than that of 760 Torr, and also found that adhesion of sprayed coatings at pressure of 200 Torr to substrate is stronger than that of 760 Torr. Besides these, the thickness of Al_2O_3 coating is about 20μm for spraying time 60sec. Therefore, we have confirmed that low pressure plasma spraying is one of the most available methods to produce high quality coatings of refractory materials.