Plasma-sprayed TiC protective coatings for fusion devices: Coating fabrication criteria

Plasma-sprayed TiC coatings are of interest as protective coatings for surfaces exposed to high energy fluxes in fusion devices. Thick, dense coatings are required primarily to withstand erosion and sputtering for long times whereas less dense coatings seem preferable for preserving a high thermal shock resistance. This study was carried out to outline the fabrication criteria needed to obtain thick TiC coatings which can withstand severe thermal shocks. TiC coatings with different microstructures (porosities) and thicknesses, plasma-sprayed under atmospheric and inert atmosphere conditions, were exposed to pulsed electron beam thermal shocks. Different microstructures were obtained after spraying TiC powders of various particle size distribution and morphology. The porosity of sprayed coatings ranges from 17% to 29%. The results obtained after thermal exposure indicate that the thermal shock resistance decreases as the TiC coating porosity increases. They also indicate that coatings obtained by spraying a narrow band powder into an inert gas enclosure contain some porosity that could help them to withstand spallation. (orig.)