SLIDING BEHAVIOR OF SELECTED ALUMINUM-ALLOYS

This project was undertaken to achieve three principal objectives: to improve understanding of the behavior of selected aluminum-based beari ng materials used in sliding applications, to develop improved guideli nes for the design of such bearings, and to respond to increasing envi ronmental concerns about the use of lead in bearing materials. Unlubri cated sliding tests have been conducted using disks of Al-Sn and AI-Pb binary alloys as well as multicomponent alloys produced with the aid of an MHD (magnetohydrodynamic) technique at the Institute for Solid S tate Physics, Chernogolovka, Russia. For comparison, commercial alloys produced by Glacier Vandervell Inc. have also been tested. The counte rface in each case was a hardened 52100 ball. Sliding speeds were kept low (15-30 mm s(-1)) to limit frictional temperature increases. Norma l loads ranged from 0.8 to 1.2 kgf. Earlier results on Pb-Sn and babbi tt alloys demonstrated that the environment strongly affects the frict ion coefficient, the smoothness of sliding and the hardness and hardne ss gradient at the surface. Therefore we have performed tests in vacuu m (as a reference condition) and in air. A range of complementary tech niques (optical and electron microscopy, X-ray fluorescence analysis u sing energy dispersive spectroscopy (EDS), microhardness) was used for structural and chemical characterization of debris and of surface and near-surface material. In all cases, sliding in vacuum was smooth and the wear rates were low. In fact, the rate of production of debris du ring the vacuum tests was negligible. However, the friction coefficien t, the fluctuations in friction and the wear rate were all much higher for tests in air. The reasons for this behavior are associated with d ramatic differences in structure and composition which develop near th e surface of the bearing material. The effects of environment are larg er than those associated with changes in composition for the alloys st udied. (C) 1997 Elsevier Science S.A.