UNDERCOOLING-INDUCED METASTABLE A-15 PHASE IN THE RE-W SYSTEM FROM DROP-TUBE PROCESSING

An A15 metastable phase is involved in the solidification path of unde rcooled Re-W alloys in a tremendously wide range of compositions (from 34 to 82 at. % W). The melting temperature of the A 15 phase reaches 3250 K at 75 at. % W. First-principles calculations were performed to determine the structural stability of the A15 phase in this system. A value of 3200 K is deduced for the melting temperature of the A15-(W) which thus appears to be the true beta phase of this element. The meta stable liquid-A15 phase diagram, that fits well the experimental resul ts, is computed by the Calphad method assuming a two sublattice descri ption of the A15 structure to simulate order-disorder phenomena.