Tin-copper alloy bearing surfaces obtained from an air compressor were examined using visual, metallographic and scanning electron microscopy techniques to determine the cause of surface degradation. The degradation consisted of pitting, grooving and metal loss that resulted in a frosted surface appearance.
There was no evidence of corrosion or mechanical damage identified. Recrystallization of the bearing contact surfaces in the degraded regions, coupled with the surface pitting and grooving, indicating the degradation resulted from electric discharge damage. The image above (55x) shows pitting features in the frosted areas.