Polymorphic Metals: Low Temp & Reversion Possibilities

[Uranium235]

Hello everyone!
I would like to know if there exists any metals with a relatively low temperature at which polymorphous takes place (say lower than 400C). Also, would the metals revert back to their previous crystalline structure if cooled down in a short period of time?

Thank you very much!

 

[Borek]

http://en.wikipedia.org/wiki/Tin_pest

This is probably not exactly what you are looking for, but as close as I can think of.