Engine Bearing Overlays: The Effect of Overlay Composition on Diffusion and Post-Diffusion Bearing Performance

At engine temperature the loss of tin and copper from the overlay of lead-tin overlay plated crankshaft bearings can result in a corrosion prone overlay and a reduction in bearing life. A nickel barrier between the overlay and the lining offers only a partial solution to the problem.

New data for the effect on diffusion rate of the original tin and copper contents of lead-tin-copper overlays have been obtained. Interactions between the tin and copper have a major effect on diffusion rate, as do the choice of barrier and its quality. The mechanisms operating during diffusion are illustrated by x-ray maps obtained on the scanning electron microscope.

Data for the post-diffusion corrosion and cavitation erosion resistance of overlays have been obtained. The results demonstrate the importance of heat-treatment at engine temperature prior to the assessment of overlay performance.