Effects of sliding speed on tribological behaviors and tribochemical reactions of alumina in HFC-134a gas

The effects of sliding speed on tribological behaviors of alumina (Al2O3) friction pairs in 1,1,1,2-tetrafluoroethane (HFC-134a) gas at 5.2×103 Pa were investigated by using a ball-on-disk tribometer. Wear tracks on the disk specimens were analyzed in situ by X-ray photoelectron spectroscopy (XPS) to identify tribochemical products. It was found that friction and wear properties of Al2O3 in HFC-134a strongly depended on sliding speed. The friction coefficient sharply increased when the speed exceeded 0.15 m/s. For the disk specimens, no obvious wears were observed. The specific wear rate of the ball showed a maximum value when speed was 0.15 m/s. The results of XPS analysis identified that tribochemical films, mainly composed of fluorinated compounds, were formed on the tracks. In addition, it was also found that the sliding speed affected the amount of the formed fluorinated compounds. More AlF3 was formed under lower speed and relative more organic compounds were formed under higher speed. The reason for sliding speed affecting the friction and wear properties of Al2O3 is that the different products formed by tribochemical reactions.