Spray-on Coatings

The high heating rates attainable using tungsten halogen and radiant plasma systems are ideally suited for the fusing of room temperature spray deposited coatings. Typically, these are carbide coatings with metallic binders. Fast fusing times (usually less than a second at temperature) minimize the dissolution of the base material which can substantially decrease the quality of the coating.

ORNL has successfully processed a multitude of carbide coatings onto various steel and aluminum alloys. The coating is applied by spray gun to the part. Once dry, the part is held at a "burn out" temperature until all of the volatiles are eliminated. The part is then rapidly taken to the fusing temperature to fuse the metallic binder. All of this is accomplished in a controlled atmosphere to eliminate oxidation.

One of the uses being explored for these coatings is the rehabilitation of die-casting pins, such as the one in Figure 1. While the finished coating will not be a thick as the "green coating" pictured, the coating may be applied in successive layers to bring the part back within tolerance.

Figure 1. Photograph of a die-pin with a chromium-carbide coating deposited, ready for fusing