Phase diagram and lattice instability in tungsten–rhenium alloys

Abstract 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≳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.