Containerless Processing of Undercooled Melts

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Abstract
Containerless drop tube processing allows for significant levels of liquid undercooling through control of parameters such as sample size, surface coating and cooling rate. A laboratory scale (3m) drop tube has been developed which allows the under-cooling and solidification behavior of powder samples to be eval-uated under low gravity free fall conditions. The level of undercooling obtained in an InSb-Sb eutectic alloy has been eval-uated by comparing the eutectic spacing in drop tube samples with a spacing/undercooling relationship established using thermal analysis techniques. Undercoolings of 0.17 and 0.23 Te were produced by processing under vacuum and He gas conditions respec-tively. Alternatively, the formation of an amorphous phase in a Ni-Nb eutectic alloy indicates that undercooling levels of approximately 500°C were obtained by drop tube processing. The influence of droplet size and gas environment on undercooling behavior in the Ni-Nb eutectic was evaluated through their effect on the amorphous/crystalline phase ratio. To supplement the structural analysis, heat flow modeling has been developed to describe the undercooling history during drop tube processing and the model has been tested experimentally.

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