Plasmaspraying

Plasmaspraying, or plasma spraying, is a thermal spray coating process in which powdered coating material is injected into a high-temperature plasma jet and propelled toward a substrate. The powder is heated to a molten or semi-molten state and impacts the surface, where it flattens and rapidly solidifies to form a lamellar coating that mechanically bonds to the substrate and to itself. The coating stack is typically deposited in layers and can vary in porosity and density depending on process parameters.

A plasma torch generates the jet by ionizing gas, usually with inert or reducing gas combinations. The powder is delivered by carrier gas through a converging nozzle and sprayed at a distance from the surface known as spray distance. The process can be performed in atmospheric or low-pressure conditions (APS or LPPS). Material options include ceramics (e.g., Al2O3, Cr2O3, ZrO2), ceramic-metal composites (cermets such as WC-Co), and metal or alloy coatings (nickel, cobalt, aluminum, titanium alloys). Common applications include thermal barrier coatings for turbines, wear-resistant coatings for cutting tools and machinery, corrosion-resistant coatings for aggressive environments, and biomedical coatings in implants.

Advantages include the ability to coat complex shapes, relatively high deposition rates, and a broad range of materials; coatings can achieve high hardness and wear resistance and improved thermal insulation in the case of thermal barrier coatings. Limitations include coating porosity and oxide content, residual stresses, potential for feedstock oxidation, and variability in adhesion depending on substrate preparation and spray parameters. Surface pretreatment such as grit blasting improves bonding. Typical coating thickness ranges from tens to hundreds of micrometers, though thicker coatings are possible.