Theoretical and experimental studies of devitrification pathways in the Zr_2Cu_(1-x)Pd_x metallic glass system

摘要

Using a model amorphous alloy series, Zr_2Cu_(1-x)Pd_x (x = 0, 0.25, 0.5, 0.75 and 1), we demonstrate that ab initio calculations can predict likely metastable phase formation during devitrification by comparing these with time-resolved X-ray scattering studies. All compositions share the same equilibrium C11_b phase, yet they follow different devitrification pathways. Only x = 0.5 leads to a metastable C16 phase formation. This corresponds precisely to calculations showing the C16 phase is closest in energy to the stable C11_b phase. The competition is shown to be dominated by electronic structure rather than size effects, with the favored composition for the C16 phase forming a pseudo-gap at the Fermi energy. All Pd-containing compounds devitrify first into a quasicrystalline phase. Zr_2Cu_(1-x)Pd_x compounds based on the NiTi_2 O_h~5 structure are higher in energy relative to the C16 and C11_b structures for all compositions, and the calculations show no increase in stability with Pd concentration.