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 ®nd that bcc W1ÿcRec does not become dynamically unstable until cJ 0:7, i.e., well above the equilibrium solubility limit of Re in bcc W. Concentration ¯uctuations of Re in irradiated W will therefore not lead to any signi®cant number of regions where the bcc lattice collapses due to a dynamical instability. Ó 2000 Published by Elsevier Science B.V. All rights reserved.