High temperature tribological properties of YSZ/AgTaO3 sol-gel nanocomposite coatings

Composite coatings whereby soft and lubricious phases were embedded in a hard matrix displayed considerable enhancement in their mechanical and tribological properties that include frictional response, wear resistance, and material toughness. In the current study, composite coatings of a yttria-stabilized zirconia (YSZ) matrix embedded with different contents of AgTaO3 particles (0-30 wt%) were prepared by a sol-gel process and subsequently deposited on Inconel 718 substrates using the spin coating technique. X-ray diffraction (XRD) measurements indicated the presence of YSZ in the cubic phase and of AgTaO3 The tribological properties of the coatings were evaluated at 25 and 650 degrees C against an alumina (Al2O3) ball using a 2 N load. AgTaO3 was found to significantly enhance the coatings' wear and friction properties especially at 650 degrees C. The addition of this high temperature solid lubricant was found to decrease the steady state friction coefficient from 0.65 to 0.18 and the wear rate from 7 x 10(-5) mm(3)/nm to 6 x 10(-6) mm(3)/nm for YSZ-30 wt%AgTaO3. Scanning electron microscopy (SEM) provided information about the surface topography and the elemental composition of the coatings before and after wear testing. SEM images suggested that an increase in AgTaO3 content resulted in the formation of a continuous film of this solid lubricant over an underlying YSZ-based coating. This continuous film provided better wear protection to the composite coating. These observations provide insights useful for developing composite coatings using the sol gel method and that display tunable tribological properties depending on the intended applications.