ok, this is starting to get way out of my area of expertise (the being having read an article on the potential of space manufacture). I only make comments about Ti and Nb in particular cuz I know a lot more about them due to my research into anodization. I am having trouble thinking of something that would be liquid at the melting temperature of Ti or Nb that would still be liquid at room temperature. Also that liquid is likely to be heavy. This would be a problem if you had closed cell foam. OTOH I guess one is stuck with the use of open cell foam even foaming with gasses (or else the foam would collapse when the gas contracts going to room temperature). Getting back to foaming with liquid I guess one could foam with liquid that solidifies at higher than room temperature. One would need to evacuate it before going to room temp. Could also be tricky in that one would need a liquid that wouldn't like to intermix/alloy with the metal being foamed (and with Ti, the liquid can't have any nitrogen, oxygen or hydrogen in it or the Ti is likely to absorb those elements and become embrittled). At this point I'm mostly just speculating now and am not sure how useful it is.
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