Alumina coatings deposited with reactive DC magnetron sputtering in a CO2/O2 gas mixture

Reactive DC magnetron sputtering was applied for the deposition of amorphous alumina coatings. Transparent coatings with a thickness of up to 2 μm were deposited on hardened high-speed steel, silicon (wafer material) and Si3N4 ceramics with typical growth rates in the region of 0.35 μm/h. The chemical composition of the coatings is comparable to alumina coatings deposited with reactive pulsed magnetron sputtering. The coatings were characterized by depth-sensing indentation measurements and by friction experiments before and after thermal treatments. The hardness and elastic modulus of the as-deposited coatings amount to 10–15 and 250–350 GPa, respectively. After annealing at 500 °C under atmospheric conditions, an increase in the hardness and the elastic modulus was observed. The friction coefficient of the coatings before and after thermal treatment against sintered tungsten carbide/cobalt balls amounts to 0.3–0.4.