Friction and wear behavior of aluminum-graphite composites as a function of interface and fiber direction

Abstract

The friction and wear behavior of aluminum-graphite fiber composites was examined as a function of the interfacial reaction zone. Sliding wear tests were performed on three different fiber orientations on a standard pin-on-disk tribology machine. The counterface was made of gray cast iron with a surface hardness of 92 HRB. The wear rate and friction coefficient were found to decrease exponentially with sliding time and eventually reached a steady state condition. This was attributed to the development of a lubricating transfer film on the sliding surface. The wear mechanism was investigated through the use of scanning electron microscopy analysis. A wear model was developed for specimens worn with fibers parallel to the sliding direction. This model incorporates three dominant wear mechanisms: (1) matrix removal by delamination, (2) fiber wear due to plowing and (3) fiber pull-out. The model was evaluated numerically and was found to agree with the experimental data. The model predicts that whenever fiber pull-out is a contributing mechanism in the wear, the wear rate is an exponential function of the normal load. In contrast, the wear rate of composites is proportional to the normal load in the absence of fiber pull-out.