Galling
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Galling can occur when metal parts, such as the threads of nuts and bolts, are forced together and rubbing generates friction among the asperities (high spots) on the surface. The friction causes heat, which is mainly isolated to these asperities. The asperities weld together but further displacement causes these tiny welds to break, which makes the surface even rougher, creating more opportunity for friction. Galling should not be confused with cold welding.
