Tungsten carbide phase transformation during the plasma spray process

Abstract

Tungsten carbide coatings applied by the plasma spray process have been widely used in wear applications. In the W–C–Co ternary system, tungsten carbide can either be present as WC or W2C. Frequently WC transforms into W2C during the plasma spray process. In this study, tungsten carbide/17% cobalt coatings were applied by both the air plasma and the vacuum plasma spray processes using different power levels and plasma gases. The W2C phase was found by X-ray diffraction techniques in the air plasma sprayed coatings. Decarburizing of the WC in the presence of the oxygen took place in the plasma. In this study air plasma sprayed coating hardness and microstructure are superior to those of the vacuum plasma sprayed ones. However the vacuum plasma coatings were found to be more wear and impact resistance than the air plasma coatings. This performance difference may be attributed to the presence of hard and brittle W2C phase in the air plasma sprayed tungsten carbide coatings.