Process Description
Controlled environment spray technology takes everything we know about plasma spray one major step further. The spray gun is operated in a chamber within a completely controlled environment. This yields coatings exhibiting unique properties not possible in standard atmospheric environments. The environment can be in the range from near vacuum (as low as 50 mbar) to elevated pressures (as high as 4 bar). Chamber spraying may be chosen to prevent contamination of the coating material and/or substrate, or because a reaction of the coating material with a specifically introduced substance is desired.

Schematic cross-section of a typical controlled atmosphere plasma spray gun

Several advantages result. Coatings are very dense, extremely well bonded, free of contamination and metallic coatings are free of oxides. Non-metallic coatings, such as ceramics sprayed in chambers backfilled with non-reactive atmospheres, are very pure. Furthermore, coatings of refractory metals, such as tungsten, can successfully be applied. The distance between the gun and the workpiece is much less critical than in atmospheric spray conditions, so part manipulation is simplified. Spray processing times can be greatly reduced because the plasma plume retains a uniform cross section and "spot diameters" can be very large. Also, the lack of atmosphere to cool the coating particles means that coating solidification takes place more slowly. There are virtually none of the interlayer "splats" exhibited by atmospheric plasma coatings and the coatings exhibit a more crystalline structure that approaches that of cast materials.

A unique feature of the controlled atmosphere spray process is the ability to use Reverse Transferred Arc (RTA) to metallurgically clean the workpiece while in the chamber, with the coating process following immediately thereafter. This greatly enhances coating bond strengths.

Schematic cross-section of a typical plasma spray gun

Features of the ChamPro® Controlled Atmosphere Plasma Spray Process:
• Produces extremely clean coatings that are nearly fully dense
• Rapid processing times
• Spraying of refractory metals is possible
• Very thick coatings are possible
• Creation of near-net shapes is possible
• Superior control of coating thickness and surface characteristics
• Flexible system configurations:
• High volume, continuous operation system configurations using one or more load lock systems and transfer chambers
• Batch processing system configurations using robotics and other unique manipulation methods
• High deposition rate
• High bond of the coating to the substrate
• In-chamber final cleaning using Reverse Transferred Arc (RTA) process
• Coating of complex geometries
• Process can be fully automated