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 undercooled Re-W alloys in a tremendously wide range of compositions (from 34 to 82 at. % W). The melting temperature of the $A15$ 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 \ensuremath{\beta} phase of this element. The metastable liquid-$A15$ phase diagram, that fits well the experimental results, is computed by the Calphad method assuming a two sublattice description of the $A15$ structure to simulate order-disorder phenomena.