Effect of testing environments on friction and bidirectional material transfer during dry sliding of 3004 aluminum against h13 steel

Dry sliding experiments of3004 aluminum pins against HI3 steel disks were performed at a load of 98 mN, sliding speed of 1 m/s and fixed sliding distance of 600 meters under vacuum and air with different relative humidities. Friction, microscopy and energy-dispersive X-ray studies showed that friction and wear increase with relative humidity and that material transfer occurs from the pin to the disk and vice-versa. The increase of friction and wear with relative humidity is believed to be due to the formation of oxide particles acting as hard third bodies ploughing into both contacting surfaces. Since oxidation is suppressed in vacuum, the relatively low wear in vacuum (compared with regular air ambients) is explained by the absence of such hard oxide particles.