MICROSTRUCTURES AND TRIBOLOGICAL CHARACTERISTICS OF ELECTRON-BEAM CO-DEPOSITED AG MO THIN-FILM COATINGS/

The tribological characteristics of surface coatings on a metal substr ate are affected by several factors including the microstructure of th e coatings, the interactions between the coating and metal substrate, and the mechanical properties of the substrate. Techniques are availab le to fabricate different types of metastable film structure to aid in unraveling their influences on tribological behavior. In this study, we investigated the friction and wear properties of thin film coatings consisting of Ag and Mo which were co-deposited by electron-beam evap oration in an ultra high vacuum. Ag and Mo were chosen because the met astable structures, such as extended solid solutions or nano-crystalli ne microstructures, can be formed by co-deposition, although alloys of the two metals cannot exist in thermodynamic equilibrium. Using a Cam eron-Plint high frequency pin-on-plate friction machine, test results show that a co-deposited film having an optimum composition ratio of A g:Mo=69:31 (denoted by Ag69Mo31), and having a thickness of 150 nm, ha s the lowest friction (20%-25% reduction) and improved anti-wear prope rties compared with coatings of other compositions. A bare steel plate after dry sliding of 30 h against a steel sphere shows substantial we ar and plastic deformation. In contrast, the same plate with a thin fi lm coating of Ag69Mo31 shows a much smoother surface. The improved tri bological characteristics may be attributed to the greater wear-resist ant and shearing capabilities of nano-crystalline binary mixtures on i ron surfaces.