Effect of Normal Loads on Tribological Properties of Bronze-Graphite Composite under Seawater Condition

A bronze 663-11.7 wt% nickel-coated graphite composite was prepared by using a powder metallurgy route. Ttribological tests were carried out to investigate the effect of normal loads on a composite with a pin-on-disc tribotester at a constant sliding speed (0.083 m/s) in seawater. The nickel-coated graphite could smear out from the matrix and acted as a solid lubricant during the sliding process. When the normal load exceeded 110 N, the friction coefficient of the composite decreased, whereas the specific wear rate of the composite increased. The obtained results indicated that 110 N was a critical threshold of applied load at which there was a transition of friction and wear regimes of the bronze-nickel-coated graphite composite. When the applied load was <110 N, the wear mechanism of the composite was abrasive wear. However, the wear mechanism was abrasive wear and severe delamination when the normal load exceeded 110 N.