Tribochemical effects on tribological properties of self-mated zirconia ceramic in HFC-134a gas

Tribochemical effects on the tribological properties of self-mated zirconia ceramic in CF3CH2F (HFC-134a) were investigated using a ball-on-disk type environmental tribometer. The friction chamber of the tribometer was attached to a micro-spot X-ray Photoelectron Spectrometer (XPS) for ensuring that surface analysis be conducted without exposuring the frictional surfaces to air. It was found that HFC-134a gas was an effective lubricant for zirconia ceramic, especially at a pressure higher than 10(3) Pa. The products of tribochemical reactions between zirconia and HFC-134a molecules were detected. The amount and chemical state of the tribochemical products seemed to control the tribological behaviors. Thus, the role of tribochemical products on the tribological properties of zirconia in HFC-134a gas at 10(4) Pa was studied in detail under applied loads of 0.6-5.0 N and sliding speed of 0.04-0.35 m/s. It was found that severe tribochemical reactions occurred at low speeds and high loads. The formation of ZrF4 accelerated the chemical wear of zirconia, and raised the friction. Zirconia ceramic is suitable for use at moderate load and sliding speed under a reactive environment.