Lubricious silver tantalate films for extreme temperature applications

Silver tantalate was investigated as a potential lubricious material for moving assemblies in high temperature tribological applications. Three different approaches were explored for the creation of such materials on Inconel substrates: (1) powders produced using a solid state which were burnished on the surface; (2) monolithic silver tantalate thin films deposited by magnetron sputtering; and, (3) an adaptive tantalum nitride/silver nanocomposite sputter-deposited coating that forms a lubricious silver tantalate oxide on its surface when operated at elevated temperatures. Dry sliding wear tests of the coatings against Si3N4 counterfaces revealed friction coefficients in the 0.06–0.15 range at T ~ 750 °C. Reduced friction coefficients were found in nanocomposite materials that contained primarily a AgTaO3 phase with a small amount of segregated Ag phase, as suggested by structural characterization using X-ray diffraction. Furthermore, cross-sectional transmission electron microscopy techniques determined that the reduced coefficient of friction at T ~ 750 °C was primarily the result of the formation of a lubricious AgTaO3 phase that reconstructs during the wear process into a mechanically mixed layer of AgTaO3, Ta2O5, and Ag nanoparticles.