Undercooling of bulk high temperature metals in the 100 meter drop tube

The 100-meter drop tube at NASA Marshall Space Flight Center provides an excellent opportunity to study the effects of containerless, microgravity processing in metals and alloys. In a series of experiments high melting temperature pure metals were melted in an electron beam furnace and dropped in vacuum. Sample sizes ranged from 0.175 to 1.2 grams. Large undercoolings on the order of 18 percent of the melting temperature were observed in Ti, Zr, Nb, Mo, Rh, Ta, and Pt. Undercoolings of 5 to 18 percent T(m) were observed in Ru and Ir. These undercooling results are consistent, repeatable, and occur in a high percentage of experiments. The experimental technique will be presented as well as the resultant microstructures of undercooled drops. The data will be discussed with respect to nucleation theory.