Wait, if you are in a vacuum and thus there is no oxidation layer, can't you just press two (identical) metals together and they will be joined because the electrons don't know which of the two objects they're in?
If you get your two surfaces very very close, sure. The problem is most non-ground metal is going to have a surface finish that is too rough for this to work.
You could squeeze things together, but this depends on part geometry.
Sure but the surfaces have to be perfectly flat to where you measure the roughness in angstroms. Not something you can perform by hand or with mechanical polishing.
