MICROSTRUCTURAL CHANGES INDUCED BY DRY SLIDING WEAR OF A A357 SIC METAL-MATRIX COMPOSITE/

The sliding wear behaviour of a commercial (Duralcan) metal matrix com posite containing 30 vol.-%SiC particles, and that of the unreinforced A357 matrix alloy were investigated in the load range 6-74 N and a sl iding speed of 1 m s(-1) against a grey cast iron counterface. At the lowest load (6 N) the wear coefficient of the composite (3.1 x 10(-6) mm(3) N-1 m(-1)) was lower than that of the monolithic alloy (169.6 x 10(-6) mm(3) N-1 m(-1)). Between 18 and 40 N the wear performance of t he two materials was very similar but at the highest load (74 N) the w ear coefficient of the composite (176.8 x 10(-6) mm(3) N-1 m(-1)) was much higher than that of the monolithic alloy (89 x 10(-6) mm(3) N-1 m (-1)). The maximum depth of friction induced deformation was found to be about three times higher for the composite than the monolithic allo y 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 alpha alumina was observed, and the presence of iron oxides indicated transfer from the counterface. Widespread cracking was found at the Si C/matrix and alpha alumina/matrix interfaces. The matrix had developed a fine subgrain structure with little evidence of the Mg2Si which was present in the starting structure.