Question: How does "cold welding" work?

Andrew Winnard answered on 10 Dec 2015:

This is a great engineering and physics question, which is not my area of exerptise, but I have learned about it just for you 🙂

Metallic surfaces touching in the vacuum can stick to each other and fuse. This is known as the “cold welding” and it seems to be a possible issue in space if it happens where it should not.

Preventing accidental cold-welding:

Materials selection: Contact surfaces could either be made of different materials that do not cold-weld, and/or of materials with low contact adhesion (dissimilar metals). Aerospace & Advanced Composites (AAC) publishes Cold Weld Database listing materials combinations and their adhesion in four categories also for fretting and impact contacts.
Coated surfaces: Selected materials can be coated (painted, anodised, oxidized, chemical film coated,…) to reduce contact adhesion. Coating effectiveness can be reduced through fretting and impact damage.
Reduce contact surface: Either by increasing margin between them, reducing surface size altogether, and/or using non-polished finish low contact area surfaces where possible.
Reduce environmental exposure: Thermally insulate parts exposed to thermal cycling, shield against micrometeorite, radiation damage, stray light induced emissions, electrostatic charge and chemical interaction (e.g. atomic oxygen) that can degrade or damage coating and/or introduce contaminants and expose bare metals prone to cold-welding.