On Earth when two pieces of metal comes into direct contact with each other, nothing amazing happens. In a complete vacuum condition the two metals fused permanently, how and why?
$\begingroup$ The Feynman quote on the Wikipedia page for cold welding pretty much explains it. $\endgroup$– ACuriousMind ♦Apr 7, 2015 at 14:42
$\begingroup$ What is your source? I suppose that it happens if the two metal surfaces are without oxide films. So even in vacuum the surfaces have to be clean from oxidation. $\endgroup$– HolgerFiedlerApr 7, 2015 at 14:53
$\begingroup$ I was browsing a children magazine about astronomy and chanced upon an interesting article mentioning this phenomenon. $\endgroup$– user6760Apr 7, 2015 at 15:01
$\begingroup$ Related: physics.stackexchange.com/q/87107/2451 $\endgroup$– Qmechanic ♦Apr 7, 2015 at 15:12
In theory, yes – it’s an effect called ‘cold welding’ by which the metallic bonds that hold atoms together in each object effectively ‘bridge the gap’ between them to create a single solid object. In practice, this rarely happens on Earth because most metals form a protective oxide layer where their surface is exposed to the atmosphere. Slight bumps and irregularities in metallic surfaces also prevent this from happening. Even when metals are taken into space, the oxide layer remains – but, of course, if you deliberately polished it off then, yes, the two metals would fuse together, and that’s something satellite and spacecraft designers need to bear in mind.