Effect of film adhesion on tribological properties of silver-coated alumina

Abstract

Soft metal films are seen as possible solid lubricants for sliding ceramics in high temperature environments. Ion bombardment of substrate and film can improve film adhesion and tribological properties of metal films deposited on ceramics. To provide a more detailed understanding of the relationship between measured adhesion strength, surface roughness, and wear performance of coatings, thin silver films were vapor deposited on smooth and roughened alumina substrates using 1 keV ion bombardment before and during deposition. A pull-type tester was used to measure the adhesion of films to the substrate. A ball-on-flat test machine was used to evaluate the wear of an uncoated alumina ball sliding on silver-coated substrates. Measurements of film adhesion and sliding wear, and a scanning electron microscopy examination of wear tracks, are reported. Ball wear on roughened surfaces was reduced by a factor of about 3 for poorly adhering coatings, but by a factor of about 130 for well-adhering coatings deposited after argon-oxygen sputter cleaning, compared with bare Al 2O 3. For films with the lowest wear, the silver coating wore off the tips of the asperities,but the film remained almost completely intact. For smooth flats, wear reductions by a factor of about 3 were obtained for well-adherent coatings.