Adhesion and wear studies of magnetron sputtered NbN films

NbN films were deposited on MS, SS and HSS substrates by reactive DC magnetron sputtering. Effects of N2 flow and substrate biasing were studied on the deposition rate, crystal structure, surface hardness, adhesion and tribology. Scratch test was carried out for adhesion evaluation. Online recording of friction, depth of indentation and acoustic emission was carried out. Critical loads for cohesive and adhesive failures were observed. Tribological evaluation was performed on wear and friction machine with reciprocating ball-on-plate configuration at 3and 6 N loads and at 5 and 15 Hz frequencies against hard chrome steel balls of 12.7 mm diameter. Coatings deposited at N2/Ar flow ratio of 0.20–0.30 and at substrate bias voltage of −50 to −75 V showed higher hardness, better adhesion and low coefficient of friction.