Abstract: A plasma spray apparatus for applying a coating to an article, wherein the apparatus includes a cup shaped plasma nozzle and a main gas nozzle coaxially surrounding the exterior of the plasma nozzle forming a passage between the main gas nozzle and the plasma nozzle through which the main gas containing powder particles is caused to coaxially flow, and a converging/diverging nozzle positioned at the exit of the plasma nozzle and main gas nozzle, having an entry chamber into which the plasma gas and the main gas with powder particles entrained therein flow and combine to establish a gas mixture, the gas mixture accelerating through the extended bore of the converging/diverging nozzle to a sonic or supersonic velocity so that upon impact onto the surface of the article a cohesively bonded coating will form and build-up.

Abstract: A method of operation of a plasma torch and the plasma apparatus to produce a hot gas jet stream directed towards a workpiece to be coated by first injecting a cold high pressure carrier gas containing a powder material into a cold main high pressure gas flow and then directing this combined high pressure gas flow coaxially around a plasma exiting from an operating plasma generator and converging directly into the hot plasma effluent, thereby mixing with the hot plasma effluent to form a gas stream with a net temperature based on the enthalpy of the plasma stream and the temperature and volume of the cold high pressure converging gas, establishing a net temperature of the gas stream at a temperature such that the powdered material will not melt or soften, and projecting the powder particles at high velocity onto a workpiece surface.

Abstract: A method of operation of a plasma torch. A cold high pressure carrier gas containing a powder material is injected into a cold main high pressure gas flow and then this combined flow is directed coaxially around a plasma exiting from an operating plasma generator and converging into the hot plasma effluent, mixing with the effluent to form a gas stream with a net temperature, based on the enthalpy of the plasma stream and the temperature and volume of the cold high pressure converging gas, such that the powdered material will not melt. The combined flow with entrained is directed through a supersonic nozzle accelerating the flow to supersonic velocites sufficient that the particles striking the workpiece achieve kinetic energy transformation into elastic deformation of the particles as they impact the workpiece forming a cohesive coating.