Evidences of transitory metastable phases in refractory metals solidified from highly undercooled liquids in a drop tube

Brightness traces of the solidification of highly undercooled Ta and Re droplets processed in an ultrahigh vacuum drop tube give evidence of two successive phase transformations. First-principles calculations of the structural stability of these metals are developed in order to appreciate the possibilities of obtaining alternative phases. Some prototype transition metal crystal structures were examined and the fcc phase for the Re and the A15 phase for Ta are possible candidates for the observed metastable phases. Good agreement is obtained between theoretical calculations and experimental measurements of their respective melting temperatures.