Metastable pressure-enabled binary solid solutions with large lattice distortions: Cr–Sc, Mo–Sc, and W–Sc

It is known that a large size mismatch between constituent atoms prevents the formation of single phase solid solutions; however, pressure presents a novel avenue to beat this immiscibility and even the opportunity to form metastable phases at ambient conditions. Furthermore, the large distortions produced by the size mismatch can have a strong impact on mechanical properties since they impede dislocation motion; therefore, they need to find new motion pathways. Large lattice distortions might also heavily influence the solution energetics of interstitial atoms. In this work, we investigate via density functional theory whether the immiscibility of Cr–Sc, Mo–Sc, and W–Sc systems can be overcome with high-pressure alloying. We have calculated the mixing enthalpy for different compositions and pressures, up to 100 GPa, for hcp and bcc crystal structures, quantified the lattice distortions, and calculated the bulk modulus. We found that some compositions of Mo–Sc and W–Sc alloys are already miscible at pressures of 15–20 GPa and could be experimentally realized as metastable at ambient conditions via a suitable temperature–pressure and quenching protocol.