Fretting

A special case of adhesive wear that can occur when two machine parts are in contact. Fretting can arise wherever there is the potential for small amplitude motion between loose-fitting parts, such as at loosely fitting impellers, beneath loose-fitting bearings, and between impeller wear rings and the impeller hub. It can also occur whenever a softer material, such as an elastomeric O-ring, rubs against a hard shaft or sleeve. Fretting can be identified by a red powdery oxide that forms along the fretted surface.