Phase diagram and lattice instability in tungsten-rhenium alloys

Tungsten has been suggested as a material in applications where it is irradiated by neutrons and undergoes transmutation to rhenium. Pure W has the bcc 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 unstable at high Re concentrations. Through a detailed calculation of the phonon spectrum, we find that bcc W1-cRec does not become dynamically unstable until c greater than or similar to 0.7, i.e., well above the equilibrium solubility 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 bcc lattice collapses due to a dynamical instability. (C) 2000 Published by Elsevier Science B.V. All rights reserved.