Variation of Vaporized Coating Material in Free Plasma Jet of Plasma Spray-Physical Vapor Deposition Process

摘要

In the Plasma Spray-Physical Vapor Deposition (PS-PVD) process, the vapor atom of feedstock material is one deposition unit of the columnar structure coating. It is reported that the gas phase may be transformed into cluster when the powder feeding rate increases from small to large or the sedimentation distance increases from a certain distance to another distance. In order to understanding the variation of vaporized coating material in free plasma jet, the gaseous material capacity of plasma jet must be fundamentally understood. In this work, the thermal characteristics of plasma were firstly measured by optical emission spectrometry (OES). The results show that the free plasma jet is in the local thermal equilibrium due to a typical electron number density from 2.1 × 10~(15) to 3.1 × 10~(15) cm~(-3). In this condition, the temperature of gaseous zirconia can be equal to the plasma temperature. A model was developed to obtain the vapor pressure of gaseous ZrO_2 molecules as a two dimensional map of jet axis and radial position corresponding to different average plasma temperatures. The overall gaseous material capacity of free plasma jet was further established. At a position of plasma jet, clusters may form when the gaseous material exceeds local maximum gaseous material capacity.