Tribological Characteristics of Particle and Chopped Fiber-Reinforced Al-Si Alloy Matrix Composites

Abstract

Reciprocating friction and wear tests of Al-Si alloy matrix composites in contact with bearing steel were conducted in air and lubricating oil to evaluate the friction and wear characteristics of the composites. In air, the coefficient of kinetic friction (μk) of the composites increases with load due to an increase in the real area of contact surfaces by metal-to-metal contact. In oil, the μk is constant above 50 N and drops with decreasing load. A parallel alumina fiber-reinforced composite to rubbing surface (PFRC) and a normal alumina fiber-reinforced composite (NFRC) exhibit good factional performance in air and oil. The frictional performance of a hollow silica particle-reinforced composite (SPRC) is the worst in air and oil because of the frictional resistance by fractured silica spheres and fragments. The wear rate (wL) of the composites in air increases with load and is much higher than that in oil. This indicates that the composites vs. the steel should not be operated under the unlubricated condition. The wL of the composites in oil also increases with load. The wL of the SPRC is as low as that of PFRC at low loads because there is still some load carrying ability of unexposed silica spheres right under the surface. It, however, increases at high loads by abrasive wear of the crushed and fractured silica fragments. Because of the better load carrying capacity of normal fibers, the NFRC exhibits better anti-wear properties than the PFRC in oil. This also indicates that the fiber orientation effect is a necessary but not sufficient factor in determining the overall behavior of the MMC vs. steel tribosystem, because the wear rate (wU) of the steel mating surface caused by the NFRC and PFRC exceeds that by the SPRC under abrasive wear conditions at high loads.