Effect of substrate bias voltage on the composition, microstructure and mechanical properties of W-B-C coatings

Commercial ceramic protective coatings usually exhibit high hardness, but low ductility impairs their performance and application-oriented properties. Accordingly, a state-of-the-art magnetron sputtered W-B-C coating can be a promising coating for the tooling industry due to its hard yet tough characteristics. In the present study, we have employed substrate biasing to enhance the delivered energy to the growing film and have investigated the effect of bias voltage on the structural and mechanical behavior of W-B-C coatings. The investigations revealed that increasing the substrate bias voltage enhanced the re-sputtering of B and C atoms and subsequently varied the chemical composition of the coatings and significantly decreased the growth rate. It also enhanced the crystallinity of the coatings. We demonstrate how the bias voltage led to an unusual transition from a featureless to a columnar microstructure. Furthermore, it was observed that as the substrate bias voltage increased from 0 V to −125 V, the compositional and structural changes resulted in a slight decrease of the hardness, while a further increase in the bias voltage to −200 V enhanced the hardness. This increase was attributed to the suppression of dislocation movement and grain boundary deformation processes by solute segregation and by lattice defects.