Editing Galling (section)

{{short description|Form of wear caused by adhesion between sliding surfaces}}
{{about|adhesion between metal surfaces|the botanical concept|bark-galling}}
{{Multiple issues|
{{Refimprove|date=November 2011}}
{{Original research|date=November 2011}}
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[[File:External Thread Galling.png|thumb|Galled threads on an [[National Pipe Thread|NPT]] fitting. (Zoom in on threads for better view)]]
[[File:Galling lump.jpg|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.]]
[[File:MildAdh Web.jpg|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 material transfer and flattening damage of the sheet's surface. This is the first stage of material transfer and galling build-up.]]
[[File:Abrassiv Web.jpg|thumb|250px|The damage on the metal sheet illustrates continuous lines or stripes, indicating a breakthrough of the oxide surface-layer.]]
[[File:SevereAdh Web.jpg|thumb|250px|The damage on the metal sheet or characteristic pattern illustrates an "uneven surface," a change in the sheet material's plastic behavior and involves a larger deformed volume compared to mere flattening of the surface oxides.]]

'''Galling''' is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together.<ref>{{cite journal | last1=Budinksi | first1=Kenneth | last2=Budinski | first2=Steven | title=Interpretation of galling tests. | url=https://www.sciencedirect.com/science/article/pii/S0043164815000290 | journal=Wear | year=2015 | volume=332 | issue=1 | pages=1185–1192 | doi=10.1016/j.wear.2015.01.022 | url-access=subscription }}</ref> Galling is caused by a combination of [[friction]] and [[adhesion]] between the surfaces, followed by slipping and tearing of [[crystal structure]] beneath the surface.<ref>{{cite journal | last1=Dohda | first1=Kuniaki | title=Galling phenomena in metal forming. | journal=Friction | year=2021 | volume=9 | issue=4 | pages=665–685 | doi=10.1007/s40544-020-0430-z | s2cid=228815215 | doi-access=free }}</ref> This will generally leave some material stuck or even [[friction welding|friction welded]] to the adjacent surface, whereas the galled material will appear worn, chipped, or even gouged and may have balled-up or torn lumps of material stuck to its surface.

Galling is most commonly found in [[metal]] surfaces that are in sliding contact with each other. It is especially common where there is inadequate [[lubrication]] between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, [[aluminium]] will gall very easily, whereas annealed (softened) [[steel]] is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.

Galling is a common problem in most applications where metals slide in contact with other metals. This can happen regardless of whether the metals are the same or different. [[Alloy]]s such as [[brass]] and [[bronze]] are often chosen for [[bearing (mechanical)|bearings]], [[bushing (bearing)|bushings]], and other sliding applications because of their resistance to galling as well as other forms of [[Abrasion (mechanical)|mechanical abrasion]].