Dry Sliding Wear Behavior of Cu-Graphite Composite within a Wide Range of Sliding Velocity

Dry sliding test was carried out to investigate the effect of sliding velocity on the wear behavior of Cu-graphite composite. The friction coefficient of the composite maintained at about 0.15 when sliding velocity below 0.5 m/s, while it increased gradually when sliding velocity exceeded 1.0 m/s. It was found that the composite showed two distinct wear mechanisms, namely mild adhesive wear and severe delamination wear. In the mild wear regime, transference from the composite to the steel surface was found at the initial stage of sliding test. The transfer occurred in a manner of "layer-by-layer", due to the solid lubrication of graphite particles. Therefore, the transferred material on the surface of counterpart had a multilayer structure. Wear particles detached from transferred layer as a result of cyclic load, and their dimension varied with increasing sliding velocity. Generally, the wear particles had a multilayer structure in this regime. As the velocity increased the shear stress in subsurface increased considerably. This led the initiation and extension of the cracks at the interface between matrix and graphite particle. Consequently the wear mechanism changed to severe delamination wear. The wear particles in this regime had large block morphology.