Effects of Environment on Friction and Wear of Al-Si Alloy Impregnated Graphite Composite

Abstract

Pin-on-disk-type wear experiments for an Al-Si alloy impregnated graphite composite (pin) in contact with a bearing steel (disk) were conducted at 100N normal load (100 Newtons) in air, argon, and deionized water to investigate the effects of environment on the tribological characteristics of the composite. The friction and wear behavior and the pin-lifting phenomenon due to wear particle ingress into the contact surfaces were continuously measured during the experiments. At low relative humidity (RH) levels, the friction coefficients in air and argon are high (0.32 to 0.39) and decrease with increasing RH to values around 0.2. The friction coefficients in air have reached a minimum of 0.15 to 0.17 between 50 and 70% RH and increased slightly at 80% RH. The friction coefficients in argon are constant at about 0.2 between 10 and 80% RH. Because of the lubricating action of a water film, the friction coefficient in deionized water is slightly lower (0.1 to 0.17) than that in air. The mean wear rate of 10−4 to 8 × 10−4 mm 3 /mm (specific wear rate; w s = 10 −6 to 8 × 10− 6 mm 2 /N) is very high in a severe wear regime at RH levels lower than 10% in air, decreases with increasing RH to a minimum in the middle RH range (30 to 60%), and increases slightly at RH levels higher than 70%. Although the mean contact pressure is very high (31.8 MPa), mild wear with the rates of 10−8 to 10−7 mm 3 /mm (w s = 10−10 to 10−9 mm 2 /N) occurs in the middle RH range. The same change in wear with RH as that in air is found in argon but the wear rate in argon is slightly lower than the wear rate in air. The height of the pin-lifting, having a wear reduction effect, is greater in argon than in air over almost the whole RH range. The wear rate in deionized water is nearly equal to the rate at 70% RH in air and argon. Presented at the STLE/ASME Tribology Conference in Ponte Vedra Beach, Florida October 26-29, 2003 Review led by Somuri Prasad