The Effect of Anion Vacancies on the Tribological Properties of Rutile (TiO2-x), Part II: Experimental Evidence

Publisher Website
Google Scholar
Abstract
Friction and wear tests were completed with the (001) and (110) planes of single crystal rutile (TiO 2-x ) specimens sliding against selected ceramic counterfaces, in well-defined crystallographic directions. The purpose of the experiments was to investigate the environmental influences on anion vacancy formation, as related to a recent hypothesis connecting oxygen substoichiometry with predictable variations in the tribological properties of rutile. The data were obtained with two, entirely different test machines operating at various loads, speeds, temperatures, sliding directions and durations, as well as test specimen atmospheres. The results independently confirmed the predicted, anion vacancy-controlled formation of certain low and high lattice (strain) energy crystallographic shear systems (i.e., Magnèli phases) and that their generation is overwhelmingly environment-dependent. The stoichiometry-controlled lattice energy of these rutile phases influences the surface and bulk shear strength (τS) of the oxide single crystal. τS values were calculated for the (001)[110] surface as a function of rutile stoichiometry. The τS of (001)[110] rutile at an estimated stoichiometry of TiO 1.93–1.98 was as low as 8 MPa, equivalent to the τS of run-in MoS2 films in high vacuum.