Atmospheric Plasma Spraying (APS) of Thin Coatings

Atmospheric Plasma Spraying (APS) is a thermal spray process performed in an open-air environment. It is used to protect components against wear, corrosion, and high temperatures.

How the Process Works

• • Plasma generation: An electric arc is created between the cathode and anode inside the plasma torch.

• • Gas supply: Process gases—argon, hydrogen, nitrogen, or helium—are passed through the arc.

• • Ionisation: The gas is converted into high-temperature plasma, reaching up to 15,000°C.

• • Feedstock injection: The coating material in powder form is injected into the plasma jet.

• • Melting: The powder particles melt almost instantly and are accelerated by the gas stream.

• • Coating formation: The molten particles strike the substrate, flatten, and rapidly solidify.

Advantages of APS

• • Wide range of materials: The process can melt virtually any high-melting-point material, including ceramics.

• • Extremely high temperature: Silicon, zirconium, and chromium oxides can be processed with ease.

• • Minimal substrate heating: The component itself is rarely heated above 150°C.

• • No thermal distortion: Low substrate temperatures minimise the risk of component warping.

• • Adjustable thickness: Coatings ranging from several tens of micrometres to several millimetres can be applied.

Disadvantages and Limitations

• • Porosity: Typical coating porosity ranges from 1% to 5%.

• • Oxidation: Processing in an open atmosphere may cause partial oxidation of metallic materials.

• • Adhesion: The bond with the substrate is primarily mechanical and is generally weaker than that achieved using vacuum-based processes.

• • Noise and radiation: The process requires effective sound insulation and protection against ultraviolet radiation.

Applications

• • Aerospace: Applying thermal barrier coatings (TBCs) to turbine blades.

• • Medical technology: Applying biocompatible hydroxyapatite coatings to implants.

• • Automotive industry: Protecting piston rings and exhaust-system components.

• • Power generation: Insulating components that operate in aggressive environments.