FRICTION BEHAVIOR OF CERAMIC FIBER-REINFORCED ALUMINUM METAL-MATRIX COMPOSITES AGAINST A 440C STEEL COUNTERFACE

This paper describes the friction behavior of kaowool (Al2O3 . SiO2) and saffil (Al2O3) fiber-reinforced aluminum metal-matrix composites (MMCs) prepared by the squeeze infiltration technique. A hypoeutectic Al-Si alloy was used as the matrix. Friction measurements were made using a ball-on-disc configuration, in which a 440C stainless steel ball was held against a rotating MMC disc. Wear tracks on MMC discs and material transfer to the steel counterface were examined using a scanning electron microscope equipped with an energy dispersive X-ray spectroscope. There were no significant differences in the friction behavior of the three MMCs and the unreinforced alloy when metallograpbically polished samples were used as test specimens. In all four cases, the friction trace was rough with large fluctuations in friction force; the coefficients of friction varied between 0.4 and 0.6. When the surface of the MMC was etched, the friction coefficient dropped to a low value of 0.18 and the stick-slip type behavior disappeared. With increase in normal load (and sliding distance), the stick-slip type behavior, characteristic of polished surfaces, reappeared. The transition from smooth to stick-slip type behavior is correlated to the microstructure and surface topography of the MMC. Factors influencing the transfer of aluminum (from the MMC disc) to steel are discussed.