PlasmaSpray

Plasma spray is a thermal spray coating process in which fine powder particles are heated to a molten or semi-molten state in a high-temperature plasma jet and then propelled onto a prepared substrate to form a coating. The technique can deposit ceramics, metals, and composite materials, yielding coatings with a range of thicknesses and properties.

In operation, a plasma torch generates a high-velocity plasma jet by ionizing a gas, typically argon with hydrogen or nitrogen. Feedstock powders are injected into the plasma, melted, and accelerated toward the substrate where they flatten, rapidly cool, and bond to create a coating. Key process variables include stand-off distance, particle size, feed rate, plasma gas composition, and torch power, all of which influence coating density, porosity, and adhesion.

Materials commonly applied by plasma spray include Al2O3 and ZrO2-based ceramics, cemented carbides, nickel- or cobalt-based alloys, and metal matrix composites such as WC-Co. Yttria-stabilized zirconia (YSZ) is widely used for thermal barrier coatings, while metallic and cermet coatings provide wear and corrosion protection. The porosity and microstructure can be tailored for specific functions, and coatings can be thick, meeting applications that require robust protective layers.

Variants of plasma spray include atmospheric plasma spray (APS), vacuum plasma spray (VPS), low-pressure plasma spray (LPPS), and suspension plasma spray (SPS), the latter enabling finer microstructures by using submicron or suspension feeds.

Applications span aerospace and power generation (turbine blades, combustion chambers), automotive and industrial machinery, and biomedical implants. Advantages include material versatility, potential for thick coatings, and strong adhesion, while limitations involve surface roughness, porosity control, possible oxidation, residual stresses, and equipment costs.