Tribological behavior and tribochemical reactions of alumina in HFC-134a environment

The tribological behavior of alumina (Al2O3) in CF3CH2F (HFC-134a) gas at pressures between 170 Pa and 105 Pa were investigated using a ball-on-disk type tribometer. For comparison, the friction test was also carried out in a vacuum (10−5 Pa) under the same experimental conditions. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ions Mass Spectrometry (TOF-SIMS) were used to identify the formation of tribochemical products. found that the friction and wear properties of Al2O3 were strongly dependent on the pressure of HFC-134a gas. A higher pressure correlated to a lower friction coefficient. When the pressure exceeded 103 Pa, the wear strikingly decreased. The results of XPS and TOF-SIMS analyses identified that tribochemical films, mainly composed of fluorine-containing organic compounds and Al-oxyfluorides, were produced on the frictional surfaces. In addition, it was found that the amount of the fluorides correlated well to the friction and wear properties, that is, the more the fluorides were, the lower were the friction and wear. The results of research indicate that HFC-134a gas has a good lubricating effect for Al2O3 ceramic, which is attributed to the formation of the tribofilms at the frictional interface.