Technology  >  Surface Engineering  >  Plasma Spraying

Process Description
Plasma Spray is perhaps the most flexible of all of the thermal spray processes as it can develop sufficient energy to melt any material. Since it uses powder as the coating feedstock, the number of coating materials that can be used in the plasma spray process is almost unlimited. A high frequency arc is ignited between an anode (nozzle) and a cathode (electrode). Process gases (generally mixtures of argon, nitrogen, hydrogen and helium) flowing between them is ionized to become a plume of hot plasma gas with that exceed the surface of the sun of 6,600 C to 16,600 C (12,000 F to 30,000 F). When the coating material is injected into the gas plume, it is melted and propelled towards the target substrate.

The processes gases used, in combination with the current applied to the electrode controls the amount of energy produced by the process. Since the flow of each of the gases and the applied current can be accurately regulated, repeatable and predictable coating results can be obtained. In addition, the point and angle that the material is injected into the plume, as well as the distance of the gun to the target, component can also be controlled. This provides a high degree of flexibility to develop appropriate spray parameters for materials with melting temperatures across a very large range.

The distance of the plasma gun from the target components, gun and component speeds relative to each other, and part cooling (usually with the help of air jets focused on the target substrate) keep the part at a controlled spray temperature that is usually in the range of 38 C to 260 C (100 F to 500 F).

Features of the Atmospheric Plasma Spray Process:
Large choice of coating materials, including metals, alloys, ceramics, cermets, carbides and others.
Coating systems are possible, using layers of different materials.
Produces surfaces for a wide variety of applications, including resistance to many different types or wear and corrosion mechanisms, desirable thermal or electrical characteristics, and surface restoration and dimensional control.
Excellent control of coating thickness and surface characteristics, such as porosity and hardness .
    •   No heat affected zone or component distortion.
    •   High deposition rate.
    •   High bond of the coating to the substrate.
    •   Coating of complex geometries.
    •   Easy masking of areas that should not be coated.
    •   Process can be fully automated.
    •   Coating of internal geometries possible.