Microwave-Driven Plasma Spraying

A new method of producing a hot plasma/gas stream for "plasma spraying powdered materials is proposed. The method uses microwaves to produce and heat the plasma. The objective of the program is to experimentally demonstrate the new method and establish scaling to commercially interesting powers. The project consists of modifying apparatus supplied by PSI for plasma spraying, then measuring the output flow temperature and velocities and testing the ability to spray materials. Microwave driven plasma spraying offers several advantages over conventional arc-driven plasma sprayers. Microwave discharges require no electrodes, thus eliminating the problems of wear associated with these elements. The discharges are also more stable, potentially improving the quality of the sprayed coating and reducing operating noise. In addition, a variety of gases, including inexpensive nitrogen, can be used as the working fluid. Ohmic and thermal losses are low, resulting in potentially high efficiencies. The discharge can operate at higher pressures at high temperatures, resulting in the high velocities of HVOF but at the high temperatures of plasma devices. This results in higher quality coatings of high melting temperature materials, such as ceramics. This capability offers significant improvement over the current state-of-the-art plasma spray technology.