Solidification of undercooled refractory metals and alloys by containerless processing

The increase in the specific requirements on materials in the high technology field is expected to give a growing importance to the outstanding properties of refractory metals. Complementary to the floating zone melting technique for directional solidification at slow velocity, containerless processing may help in defining novel complex alloys under conditions of non-equilibrium thermodynamics. Interest of such a processing can be discussed through the undercooling experiments realized so far with the 48 m high Grenoble drop-tube. Experience has been focused on nucleation in pure metals and phase selection phenomena in Re-(W, Ta, Nb, Mo) alloys, leading to an insight into the so-called rhenium effect. Systems characterised by the presence of a miscibility gap in the solid state (e.g. Zr-Ta) have been also considered. Attracting perspectives are open for advanced Nb-based alloys as well as for alloys combining refractory b.c.c. metals with noble metals (Pt or Ir).