Effect of temperature on tribological performance of a silicon nitride ball material with a linear perfluoropolyalkylether

The effect of temperature in rolling contact performance of a hot isostatic ally pressed (HIP) silicon nitride ball material with a linear perfluoropol yalkylether (PFPAE) was studied using a ball-on-rod type rolling contact fa tigue tester. The test temperature ranged from ambient to 343 degreesC for a period of 24 h at a stress of 5.5 GPa using thin dense chrome (TDC)-coate d T-15 bearing races. The lubricant and its decomposition products, specifi cally acid fluoride and acids, attacked Si3N4 balls at all test temperature s resulting in corrosion pitting. The presence of metal fluoride on all the Si3N4 transferred from the races, was detected by X-ray photon spectroscop y (XPS). The thickness of the oxide layer formed on the balls, as determine d by Auger electron spectroscopy (AES) increased with temperature. The chan ges in physical properties of post-test lubricant showed that me lubricant was stable at temperatures up to 288 degreesC. The change in viscosity was constant up to 288 degreesC and with a significant change above 288 degrees C. The FTIR analysis of 316 and 343 degreesC post-test lubricant showed the presence of carboxylic acid. The total acid number (TAN) increased linearl y up to 288 degreesC and accelerated at 316 and 343 degreesC. The study ind icates that the use of Si3N4 balls with a linear PFPAE results in an incomp etent tribe system.