A METALLOGRAPHIC STUDY OF WEAR IN PLANAR-RANDOM FIBER-REINFORCED COMPOSITES WITH AN ALUMINUM ZINC COPPER ALLOY MATRIX

Dry wear tests carried out on planar-random metal matrix composites with an aluminium-zinc alloy matrix and delta-alumina fibre reinforcement showed large differences in wear rates depending on the predominant orientation of the fibres relative to the sliding surfaces. The surfaces and sections through the surfaces of the wear pins were examined by scanning electron microscopy to determine the causes of this behaviour. Comparison of images obtained in secondary electron contrast with those obtained in backscattered electron contrast allowed a correlation between wear rates and structures of the surface and subsurface layers developed during wear testing. It was found that the presence of fibres reduced the amount of subsurface plastic deformation, but the large reduction in wear rate compared with the unreinforced matrix alloy was principally due to the presence of hard particles of delta-alumina fibres embedded in the surface. The orientation dependence came about because any alumina fibres lying parallel to the surface were easily pulled out and lost whilst those lying normal to the surface were broken off in small pieces and incorporated in the surface layer of deformed matrix metal, oxides and other debris.