What Does Galling Mean?
Galling is a type of wear that occurs when materials that are compressed against one another are put into motion that causes friction. When the compressive forces in conjunction with the forces causing the sliding motion are sufficient then friction creates heat sufficient to weld the materials together. This unintentionally removes material from one material and places it onto the other material.
Corrosionpedia Explains Galling
Galling is different than normal abrasive wear. During abrasive wear, material is removed through the forces of compression and translation. When galling occurs, the materials are actually bonded together. If they are able to be separated, at least one of the materials will be damaged during the removal process. The surrounding areas where the heat from friction was insufficient to join the materials together may be subject to abrasive wear.
Galling frequently occurs when fastening threaded objects together. Stainless steel and aluminum fasteners are especially prone to galling. Stainless steel and aluminum form a protective layer that helps to lessen the effects of wear and corrosion on the underlying material. However, this oxide layer will be broken when high compressive forces are introduced and allow the stainless steel or aluminum to more easily bond with the metal it is in contact with. When galling occurs on threaded materials, the threaded components might need to be severed in order to separate the connection.
Galling can be prevented by reducing the amount of friction or the forces involved. Friction can be reduced through the use of a lubricant. Reducing the force can mean lessening the load on the materials. It can also be prevented by reducing the speed at which the materials translate across each other.