Influence of WC/C target composition and bias potential on the structure-mechanical properties of non-reactively sputtered WC coatings

Physical vapor deposited WC based coatings strongly vary in their microstructure ranging from multi-phased columnar-crystalline up to nanocomposite coatings in relation to the usage of reactive or non-reactive carbon sources. Within this study, we investigated in detail the influence of additional carbon implemented into WC based target mmaterials as well as bias potential on the structure-mechanical properties of non-reactively sputtered WC coatings. Providing additional graphitic carbon within WC targets promotes the formation of nanocrystalline morphologies. Increasing bias potentials dominate the transition from a nanocrystalline to a columnar-crystalline morphology obtaining also a mixed state in between. The change in morphology is accompanied by a large modification in mechanical properties with hardness values ranging from 27 to 39 GPa, respectively. In addition, high adatom mobility – caused by bias potentials up to −200 V – predominates the phase formation of crystalline WC coatings changing from face-centered cubic (fcc)-WCx to competing W2C based structures. The W—C phase formation is furthermore examined using DFT calculations.