| Plasma spraying is the process of injecting particles into a hot plasma plume where they are heated and propelled towards a substrate forming a coating. The effects of major operating parameters such as current, gas flow rates, gas chemical composition and powder feed rates, on the torch and coating behavior will be discussed. Torch characteristics studied include energy efficiencies, arc voltage drops, plasma jet geometry and fluctuations, and particle trajectories and velocities. Coating characteristics include deposition efficiency, spray pattern, porosity, and trapped unmelted particles.; Design of experiment techniques are used to evaluate statistical significance of operating parameters on the torch and coating response. A high shutter speed CCD camera is used to capture images of the fluctuating plasma jet. This camera used in conjunction with two pulsed nitrogen lasers is used to obtain double exposed images of particles traveling within a plasma jet. Dividing the separation distance of the double exposed particles by the gated laser pulse time difference leads to the evaluation of particle velocities. Image analysis is used to evaluate both the jet geometry and particle velocity as well as to evaluate the coating cross section images.; Several new torch designs have been developed and tested based on results and observations of operating a standard commercial torch. One torch design in particular, the "anti-vortex" torch, is shown to be effective in counteracting the negative influences of vortex arc gas flow on the powder trajectory. |
