THE EFFECT OF ANION VACANCIES ON THE TRIBOLOGICAL PROPERTIES OF RUTILE (TIO2-X) .2. EXPERIMENTAL-EVIDENCE

Friction and wear tests were completed with the (001) and (110) planes of single crystal rutile (Tio2-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., Magneli 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 ts of (001)[110] rutile at an estimated stoichiometry of TiO1.93-1.98 was as low as 8 MPa, equivalent to the τs of run-in M0S2 films in high vacuum. © 1990 Taylor & Francis Ltd.