Atmospheric Plasma Spray Process Overview
The standard plasma spray, often called air or atmospheric plasma spray, operates with plasma temperatures in the particle heating zone between roughly 6000 and 15,000 °C (11,000 to 27,000 °F), well above any material’s melting point. Plasma is generated by superheating an inert gas—commonly argon or an argon-hydrogen mixture—via a DC arc. Powder feedstock is introduced with an inert carrier gas and accelerated by the plasma jet toward the target. Cooling or controlling spray rate is necessary to keep substrate temperatures within 95 to 205 °C (200 to 400 °F). Commercial plasma spray guns range from 20 to 200 kW, and spray rates depend heavily on gun design, plasma gases, powder injection, and feedstock characteristics including particle size, distribution, melting point,
morphology, and density.
Components of Atmospheric Plasma System
- Gas supply
- Gas hoses
- Gas regulators for plasma and powder carrier gases
- Gas flow controls, usually rotameters or mass flowmeters/controllers
- Plasma arc spray gun comprising a torch body, anode/nozzle, cathode, gas ring (gas injector), and powder injector
- Electrical controls for arc current and voltage
- Direct-current power supply, typically a constant-current type
- High-frequency RF spark arc ignition source
- Water-cooling circuit
- Feedstock delivery: powder feeder
- Water-cooled power cables
- Hoses/cables
- Safety interlocks and console purging
Coating Characteristics
The plasma arc generates a hot gas jet that entrains, heats, and accelerates powder particles to the substrate, where they flatten, deform, and resolidify into coatings. The high melting and velocity result in coatings with higher density and bonding strength than most flame or electric arc spray coatings. Plasma-sprayed coatings achieve porosity as low as or lower than HVOF and detonation gun coatings—often exceeding 99% density, depending on material and equipment. The coating microstructure quality arises from high particle kinetic energy causing deformation and flow during impact.