By looking at the process, we begin to understand the factors that affect galling:
Heat certainly promotes galling. During movement the adhesion scales with heat and in-service, heat increases the creep penetration of those high points. This leads to additional potential initiation sites for galling. Whether it’s during movement or in-service, nothing ever gets hot enough to actually melt the metal. There’s never any liquid phase.
Ductility also promotes galling. It takes energy to create a new surface because at some level you have break the internal bonds. This is related to a material’s surface energy. So, in brittle fracture, energy goes to creating the new surface. In ductile fracture, however, energy also goes into deforming the material and is stored as heat. And, again, that higher localized heat increases adhesion.
Oxide layers are a little trickier. They certainly inhibit galling and cold welding, by physically getting in the way of the underlying bulk metals. They are also typically brittle, thereby providing an energy storage mechanism. However, in some cases the volume change and debris can effectively promote galling by reducing clearances and increasing initiation sites.
Now that we know more about the galling phenomenon and process, we can begin to look for solution paths.
One solution that we all employ is lubrication. Liquid and grease-based lubricants form a film thicker than the asperities, preventing metal-to-metal contact. However, these lubricants evaporate slowly over time, reducing their effectiveness.