The effects of deposition conditions on hydrogenation, hardness and elastic modulus of W-C:H coatings

The additions of C2H2, CH4 and H2 in hybrid PVD-PECVD of W-C:H coatings deposited using High Power Impulse Magnetron Sputtering (HiPIMS) and High Target Utilization Sputtering (HiTUS) were investigated to determine their effects on the content and chemical composition of the amorphous carbon-based boundary phase and mechanical properties of the coatings. Substantial differences were observed: CH4 always produced higher concentrations of hydrogen and lower concentrations of carbon than C2H2 and HiPIMS resulted in higher contents of amorphous carbon-based boundary phase and higher levels of its hydrogenation than HiTUS. The detrimental effects of higher carbon and hydrogen contents in the boundary phase on hardness and indentation modulus were attributed to the consumption of CC bonds by CH bonds during hydrogenation and reduction of cross-linking of the polymeric network in the boundary phase. The HiPIMS W-C:H coatings deposited with acetylene and hydrogen exhibited medium (∼20 GPa) hardness and elastic modulus (200–220 GPa) with HIT/EIT > 0.1 suggesting improved toughness and wear resistance. These properties were attributed to the optimum combination of hydrogenation, hybridization and cross linking in the carbon-based boundary phase.