Microstructural changes induced by dry sliding wear of a A357/SiC metal matrix composite

Abstract

The sliding wear behaviour of a commercial (Duralcan) metal matrix composite containing 30 vol.-%SiC particles, and that of the unreinforced A357 matrix alloy were investigated in the load range 6-74 N and a sliding speed of 1 m s⁻¹ against a grey castiron counterface. At the lowest load (6 N) the wear coefficient of the composite (3.1 × 10⁻⁶ mm³ N⁻¹ m⁻¹) was lower than that of the monolithic alloy (169.6 × 10⁻⁶ mm³ N⁻¹ m⁻¹). Between 18 and 40 N the wear performance of the two materials was verysimilar but at the highest load (74 N) the wear coefficient of the composite (176.8 × 10⁻⁶ mm³ N⁻¹ m⁻¹) was much higher thanthat of the monolithic alloy (89 × 10⁻⁶ mm³ N⁻¹ m⁻¹). The maximum depth offriction induced deformation wasfound to beabout three times higher for the composite than the monolithic alloy at a load of 74 N. Detailed TEM was performed on the surface of the composite. The SiC was found to be fragmented. Extensive formation of a alumina was observed, and the presenceof iron oxides indicated transfer from the counterface. Widespread cracking was found at the SiC/matrix and lI. alumina/matrixinterfaces. The matrix had developed a fine subgrain structure with little evidence of the Mg₂Si which was present in the startingstructure.