TRIBOLOGICAL BEHAVIOR AND SURFACE ANALYSIS OF TRIBODEFORMED AL ALLOY-50 PCT GRAPHITE PARTICLE COMPOSITES

A low-pressure infiltration-casting technique was used to produce Al alloy (2014)-50 vol pct graphite particle composites. The tribological behavior of the worn surfaces of the above composites was investigated. It was found that the coefficient of friction was of the order of 0.2 as compared to over 0.4 for the matrix alloy and stabilized after a running distance of the order of 5 m. In addition, the wear rate for the composite alloys is lower and decreases after sliding distances of the order of 2 m under conditions of 10 N and 0.1 m/s. The reduced friction and wear rate of the composites as compared to the base alloy are presumably due to the formation of a solid lubricating film at the surface. Detailed X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses show that this lubricating film is approximately 10 to 20-nm thick and is composed of a carbonaceous mixture of primarily graphitic carbon plus some carbon oxides and air-deposited hydrocarbons in the film. In addition, some aluminum-containing particles also are present in the film.