First-principles prediction of superplastic transition-metal alloys

Superplastic transition metal alloys and compounds are predicted from first principles calculations. Provided a suitable tuning of the alloying is done, materials with vanishingly low shear modulus C^' have recently been identified among the $3d$, $4d$, and $5d$ elements if the valence electron average number is close to 4.24 (i.e., Ti-Ta-Nb-V-Zr-O and Ti-Nb-Ta-Zr-O alloys). The vanishingly low C^' elastic constant of these bcc alloys is, according to the joint experimental and theoretical studies [T. Saito et al., Science 300, 464 (2003)], the crucial material parameter that is responsible for the superplasticity. We predict here, using first principles calculations, that superplastic alloys should also be found for alloys with drastically different valence electron concentrations, i.e., for W-Re-, W-Tc-, Mo-Re-, Mo-Tc-, and Fe-Co-based alloys.