CHARACTERIZATION OF A SPUTTERED AMORPHOUS W-C-CO COATING ANNEALED IN AIR

In order to evaluate the suitability of sputtered amorphous W-C-Co films for applications where temperatures as high as several hundred degrees Celsius may be reached, a film deposited from a WC-15 wt.%Co target was annealed in air at increasing temperature. Besides the structure morphology and chemical composition of the film, the hardness and the scratch test adhesion were also studied. Oxidation began at 500-degrees-C with the formation of WO3 and CoWO4. At higher temperatures these oxides developed in layers, the external layer being CoWO4 and the internal layer WO3. These layers spall off at very low scratch loads. However, the remaining W-C-Co coating continues to be very adherent to the substrate. Only for a 700-degrees-C annealing temperature, when crystallization of the remaining W-C-Co film occurred, was cohesive failure of the W-C-Co layer observed.