Visual, metallographic and scanning electron microscopy techniques were used to determine the cause of surface degradation on a Tin-copper alloy bearing from an air compressor. 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.