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

Abstract

The effect of temperature in rolling contact performance of a hot isostatically pressed (HIP) silicon nitride ball material with a linear perfluoropolyalkylether (PFPAE) was studied using a ball-on-rod type rolling contact fatigue tester. The test temperature ranged from ambient to 343 °C for a period of 24 h at a stress of 5.5 GPa using thin dense chrome (TDC)-coated T-15 bearing races. The lubricant and its decomposition products, specifically acid fluoride and acids, attacked Si₃N₄ balls at all test temperatures resulting in corrosion pitting. The presence of metal fluoride on all the Si₃N₄, transferred from the races, was detected by X-ray photon spectroscopy (XPS). The thickness of the oxide layer formed on the balls, as determined by Auger electron spectroscopy (AES) increased with temperature. The changes in physical properties of post-test lubricant showed that the lubricant was stable at temperatures up to 288 °C. The change in viscosity was constant up to 288 °C and with a significant change above 288 °C. The FTIR analysis of 316 and 343 °C post-test lubricant showed the presence of carboxylic acid. The total acid number (TAN) increased linearly up to 288 °C and accelerated at 316 and 343 °C. The study indicates that the use of Si₃N₄ balls with a linear PFPAE results in an incompetent tribo system.