Phase diagram and lattice instability in tungsten-rhenium alloys

Tungsten has been suggested as a material in applications where it is irrad iated by neutrons and undergoes transmutation to rhenium. Pure W has the bc c lattice structure. According to the equilibrium phase diagram about 30 at .% Re can go into a bcc W-Re solid solution. However, ab initio electronic structure calculations show that the bcc lattice becomes dynamically unstab le at high Re concentrations. Through a detailed calculation of the phonon spectrum, we find that bcc W1-cRec does not become dynamically unstable unt il c greater than or similar to 0.7, i.e., well above the equilibrium solub ility limit of Re in bcc W. Concentration fluctuations of Re in irradiated W will therefore not lead to any significant number of regions where the bc c lattice collapses due to a dynamical instability. (C) 2000 Published by E lsevier Science B.V. All rights reserved.