FABRICATION OF TUNGSTEN COATINGS AND MONOLITHS USING THE VACUUM PLASMA SPRAY PROCESS

Tungsten is used in space nuclear power and propulsion applications fo r heat pipes, nuclear fuel cladding, and radiation shields. In this st udy, heat pipes were fabricated by vacuum plasma spraying tungsten pow der onto tungsten tubes made with the chemical vapor deposition proces s. Five experiments were conducted using a statistical design of exper iment. The varied parameters included electrical current, secondary-to -primary gas flow ratio, and total flow. The coating attributes evalua ted were thickness, porosity, microhardness, surface roughness, and gr ain structure. After the tungsten samples were thermal cycled in a vac uum, the coating qualities were evaluated with respect to the influenc e of the processing parameters. This work presents a parameter-propert y-performance relationship for the process and an optimized coating de sign predicted by the Taguchi analysis.