اهتراء المعادن بالاحتكاك

thumb|Galling on the threads not protected by PTFE tape on a NPT fitting (zoom in on first few threads for better view). thumb|250px|An electron microscope image shows transferred sheet-material accumulated on a tool surface during sliding contact under controlled laboratory conditions. The outgrowth of material or localized, roughening and creation of protrusions on the tool surface is commonly referred to as a lump. thumb|250px|The damage on the metal sheet, wear mode, or characteristic pattern shows no breakthrough of the oxide surface layer, which indicates a small amount of adhesive mater