Characterization of Plasma Jet in Plasma Spray-Physical Vapor Deposition of YSZ Using a <80 kW Shrouded Torch Based on Optical Emission Spectroscopy

During plasma spray-physical vapor deposition (PS-PVD) of yttria-stabilized zirconia (YSZ) coatings, evaporation of the YSZ powder is essential, but quite difficult when using a commercial <80 kW plasma torch. In this study, a shrouded plasma torch was examined to improve the YSZ evaporation. The plasma characteristics were diagnosed using optical emission spectroscopy. Results showed that the electron number density in the plasma jet was maintained at an order of magnitude of 10¹⁴ cm⁻³, indicating local thermal equilibrium of the plasma jet. Compared with a conventional torch, the shrouded torch resulted in much higher plasma temperature and much lower electron number density. With the shrouded torch, more energy of the plasma was transferred to the YSZ material, leading to more evaporation of the YSZ powder and thereby a much higher deposition rate of the YSZ coating. These results show that use of a shrouded torch is a simple and effective approach to improve the evaporation of feedstock material during PS-PVD.