What is Atmospheric Plasma Spray ?

What is Atmospheric Plasma Spray ?

The conventional plasma spray process is commonly referred to as air or atmospheric plasma spray (APS). Plasma temperatures in the powder heating region range from about 6000 to 15,000 °C (11,000 to 27,000 °F), significantly above the melting point of any known material. To generate the plasma, an inert gas—typically argon or an argon-hydrogen mixture—is superheated by a dc arc. Powder feedstock is introduced via an inert carrier gas and is accelerated toward the workpiece by the plasma jet. Provisions for cooling or regulating the spray rate may be required to maintain substrate temperatures in the 95 to 205 °C (200 to 400 °F) range. Atmospheric plasma spray guns operate in the range of 20 to 200 kW. Accordingly, spray rates greatly depend on gun design, plasma gases, powder injection schemes, and materials properties, particularly particle characteristics such as size, distribution, melting point, morphology, and apparent density.
Components of Atmospheric Plasma System
Coating Characteristics
In plasma sprayed coatings, the hot gas jet created by a plasma arc expands, entrains powder particles, heats the particles, and accelerates them toward the substrate, where they impact, deform, and resolidify to form a coating. The high degree of particle melting and relatively high particle velocity of plasma lead to higher deposit densities and bond strengths compared to most flame and electric arc spray coatings. The low porosity of plasma sprayed coatings can equal that of HVOF and detonation-gun-type coatings, exceeding 99%, depending, of course, on material properties, gun type, and configuration. The high quality of a plasma spray coating microstructure results from the high particle/ droplet kinetic energy, which effectively deforms the impacting particles, and the high degree of heating/melting that facilitates particle deformation and flow.