Initially, the Atmosphere and Temperature Controlled (A.T.C.) Plasma Spraying Process was developed to successfully deposit oxygen-sensitive materials on heat-sensitive substrates. The development of the three following industrial applications will be considered:
- double coatings onto small complex geometrical shapes
- freestanding B4C louvers to protect the walls of a chamber containing a high-powered laser
- large freestanding manufactured pieces, as for example, the ceramic carriers for an X-ray telescope.
The first application is a classical use of the A.T.C. process: a ceramic deposition was obtained using a ternary Ar/H2/He plasma gas mixture on a heat-sensitive substrate with rapid cooling using liquid CO2. This cooling process was required to maintain the substrate surface temperature at 35 C in order to avoid a difference of thermal dilation between the substrate and the coating. Particular care was given to the programming of the displacement of the robot for spraying and cooling because of the complex geometrical shape of the substrate.
The two other applications use the plasma forming technique to obtain freestanding workpieces. In the first case, the production of B4C ultra high-density workpieces required a high powered Ar/H2 plasma in an oxygen free enclosure. Consequently, to limit thermal stresses, a rapid liquid argon cooling process was required. In the second case, the same technique was used to produce 600 mm wide Al2O3-TiO2 freestanding workpieces that were the lightest and stiffest possible. Here, the cooling was done with liquid CO2 while the plasma spraying conditions were also with Ar/H2 gas.