Dry sliding wear of Al/Saffil/C hybrid metal matrix composites

Tribological behaviour of Al/Saffil/C hybrid composites with various amounts of graphite and alumina fibres, produced by the squeeze casting method, was studied. Preforms with about 6.5–15.0% (all the percentages v/v) of Al2O3 fibres (Saffil) and 1.5–12.0% of graphite were infiltrated under the pressure of 75 MPa. The effects of the applied load, form of graphite, and the reinforcement volume fraction on dry sliding friction were investigated using reciprocating movement. Comparison of the wear losses for the monolithic Al–Si7 matrix and its composites revealed that alumina fibres improved this property but addition of graphite improved seizure resistance. The composites reinforced with graphite fibres were less sensitive to the applied load than both the matrix and the composites reinforced with graphite flakes. During microscopic observation crushed graphite fibres and segments of alumina fibres embedded in the matrix on the wear surface were frequently observed. In the case of the composite with flake graphite, weak layers of the matrix broke and delaminated above a graphite pocket. This produced cavities of graphite, which were subsequently mixed with debris and, as the wear test was continued, these holes joined together along the direction of the counterpart movement.