The role of products of tribochemical reactions on the friction and wear properties of alumina/silicon carbide couple sliding in HFC-134a gas

By using a ball-on-disk type tribometer installed in a high vacuum chamber, tribological behaviour of a silicon carbide (SiC) disk sliding against an alumina (Al2O3) ball in CF3CH2F (HFC-134a) gas at pressures between 170 and 105 Pa were investigated. For comparison, friction tests were also carried out in a vacuum (10−5 Pa) under the same experimental conditions. Surface analysis of the wear tracks on the disks was conducted using X-ray photoelectron spectroscopy (XPS) without exposure to air. It was found that there was a significant pressure influence on both the tribological properties and products of tribochemical reactions. When the pressure increased from vacuum to 105 Pa, the friction and wear dramatically decreased, whereas the amount of carbon-containing compounds and fluorides on the wear track rapidly increased. The more vigorous the tribochemical reaction was, the lower were the wear rates, however, friction coefficient was dependent on the composition of the products of the tribochemical reactions. The metal fluorides, organic compounds formed were effective for reducing friction. On the contrary, the –Si–Fx containing compounds formed resulted in an increase in friction.