ALUMINUM METAL MATRIX COMPOSITES TAILORED FOR ANTIFRICTION APPLICATIONS

This paper describes the friction behavior of aluminum metal matrix composites (MMCs) reinforced with kaowool (Al2O3.SiO2) fiber. Composites were produced by squeeze infiltration of fiber pre-forms. A hypoeutectic Al-Si alloy was used as the matrix. Friction measurements were made using a ball-on-disc configuration in which a type 440C stainless steel ball was held against a rotating MMC disc. A polished surface produced by standard metallographic polishing and an etched surface (with protrusions of fibers and eutectic silicon) were used as test surfaces. Wear scars and steel balls (after the wear test) were examined in a scanning electron microscope. When metallographically polished surfaces were used as test specimens, the friction coefficient varied between 0.4 and 0.5; the friction trace was rough with large fluctuations in frictional force. Smearing of aluminum was detected on the steel ball as well as on the wear scar. When etched surfaces were used as test specimens, the friction coefficient was reduced to 0.15 and aluminum transfer to the counterface was completely eliminated. The results of this study indicate that microstructural control coupled with etching can be used to tailor the aluminum MMCs for antifriction applications.