High temperatures tribological properties of Ta-Ag films deposited at various working pressures and sputtering powers

The tribological performances of Ta-Ag films are greatly influenced by their composition and depositing parameters. In this study, Ta-Ag films were deposited on carbon steel substrate by DC magnetron sputtering. To adjust microstructures of the films, the sputtering pressures were controlled between 0.2 Pa and 0.6 Pa, and the sputtering powers of silver target were varied from 10 W to 25 W. The result was shown that the α-Ta phase (bcc) was obtained at lower pressure and higher sputtering power of Ag. And the contents of Ag in the films increase as the sputtering power of Ag increases. The high silver contents in the deposited films at 0.4 Pa (24.66 wt% and 31.10 wt% for Ta-Ag15 and Ta-Ag25 films, respectively) contribute to a low friction at RT, while the tribo-chemical reaction products on the frictional surface are responsible for the friction reduction at high temperatures. Low friction coefficient (~0.2) was presented for the Ta-Ag25 film when rubbing against Si3N4 ball at RT, 200 °C and 700 °C.