Friction–wear behavior and tribochemical reactions of different ceramics in HFC-134a gas

The friction and wear properties of the ionic ceramics Al2O3 and ZrO2, and the covalent ceramics Si3N4 and SiC rubbing against an Al2O3 ball in vacuum (10−5 Pa) and in CF3CH2F (HFC-134a) gas at 104 Pa were investigated using a ball-on-disk type tribometer. Without exposure to air, the surface composition and chemical state of the wear tracks and debris on the disks were determined with X-ray photoelectron spectroscopy (XPS). It is found that HFC-134a gas significantly reduces the friction and wear of all the ceramic couples, and that the ionic ceramic pairs show lower friction and wear. On the other hand, metal fluorides and/or fluorine-containing organic compounds are detected on the sliding surfaces. The differences in the friction–wear behavior of the ceramics rubbing in HFC-134a gas may be due to the products of tribochemical reactions, which are dependent on the bond type of the ceramics.