Cold Welding

Cold welding is a phenomenon that can occur in a vacuum environment, in which clean metallic surfaces brought into direct contact can bond together due to the absence of intervening gas or contaminant layers. Without adsorbed gases or surface oxides, intimate atomic contact allows the materials to adhere strongly, effectively forming a solid bond without the application of heat.

To mitigate cold welding in spacecraft, bearings, gears, and rotary joints are commonly manufactured from dissimilar or non-metallic materials, such as ceramics, or are treated with surface coatings and solid lubricants. In some cases, moving components are enclosed in pressurised or sealed assemblies to prevent direct metal-to-metal contact in vacuum.

Cold welding is most likely to occur between similar, ductile metals under load and relative motion, and is a significant design consideration for long-life spacecraft mechanisms.