Study and modelling of nucleation and phase selection phenomena:: Application to refractory metals and alloys from drop-tube processing

The demand for metallic materials for applications at high temperature is constantly rising leading to significantly more consideration of refractory metals. The study of nucleation and phase selection phenomena is of vital importance, especially when cubic and compact metals are alloyed, due to the possible formation of intermetallic compounds. In this perspective, containerless processing under weightlessness conditions is particularly needed as these materials usually feature high melting temperatures and high densities. Since large undercoolings of bulk refractory samples can be obtained only during few seconds, experiments can be undertaken on earth by letting single droplets fall within a high drop-tube facility. In this contribution, we present characteristic studies, already published or in progress, realized in the 48-m high Grenoble drop-tube with the support of the French (C.N.E.S,) and European (E.S.A.) Space Agencies. Technical restrictions are indicated justifying the request for a dedicated containerless apparatus aboard the International Space Station for complementary key experiments on refractory materials.