Structural behaviour of sputtered W-C-Co coatings at increasing temperatures

Abstract

In order to evaluate the thermal resistance of sputtered W-C-Co coatings, a structural study was carried out on amorphous and crystalline coatings according to their cobalt content after having been annealed at increasing temperatures up to 800 °C. All the films were stable up to 700°C, at which temperature the amorphous films began to crystallize as α-W2C; for higher temperatures the α-W2C carbide evolves to M6C, the extent of which increases the higher the cobalt content; for low cobalt content films WC carbide was also formed. Crystalline films have similar structural transformations, although the M6C phase is almost non-existent and α-W2C and WC can occur with preferential orientations. In all cases, the films after annealing were carbon-deficient in relation to the results obtained for the as-deposited conditions; in spite of the fact that the phases detected after crystallization are also carbon-deficient, these results are not consistent which implies that some free carbon should exist in the annealed films.