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.