Published jointly by the Minerals, Metals & Materials Society and ASM International
Metallurgical and Materials Transactions A, Physical Metallurgy and Materials Science vol:33 issue:12 pages:3847-3859
Fretting tests under dry unlubricated conditions (22 degreesC to 25 degreesC, 50 to 55 pct RH) were performed on monolithic TiB2, TiB2-based cermet with a Ni-3(Al,Ti) binder, sialon-TiB2, and ZrO2-TiB2 composites to assess their relative wear performance against bearing-grade steel. Based on the measured friction and wear data, the relative ranking of the investigated fretting couples is established. The fretting wear of all investigated tribocouples was found to fall in the tribochemical wear regime. The extent of the tribochemical reaction was observed to be strongly dependent on the chemical solubility of TiB2 and the binder phases in steel at the tribocontacts and was accompanied by tribo-oxidation. For the monolithic TiB2 and TiB2-based cermet materials, however, abrasion and adhesive wear, in addition to the tribochemical reactions, are found to be the cause for the high volumetric wear loss of these tribosystems. On the other hand, mild abrasion coupled with reduced tribochemical reactions is observed to play a major role in the low wear loss of the ZrO2-TiB2/steel fretting couple. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis of the tribochemical layer formed in the monolithic TiB2/steel tribocouple revealed the formation of mixed oxides containing predominantly TiO2 (anatase), B2O3, and Fe2O3. Based on the thermodynamic calculations and the experimental observations, a tribochemical wear model is proposed to explain the observed tribological behavior of the investigated tribosystems.