Inelastic neutron scattering study of the hydrogenated (Zr55Cu30Ni5Al10)99Y1bulk metallic glass

Abstract

The lattice dynamics of both as-charged and room-temperature-aged, hydrogenated bulk metallic glasses (BMGs) with the stoichiometry of (Zr${}_{55}$Cu${}_{30}$Ni${}_{5}$Al${}_{10}$)${}_{99}$Y${}_{1}$ have been investigated by inelastic neutron scattering at 4 K. The vibrational density of states of dissolved hydrogen atoms in the as-charged BMG shows a broad band maximized at \ensuremath{\sim}135 meV. Three months of room-temperature aging caused this band to narrow somewhat, losing intensity at both lower and higher energies. The results suggest that hydrogen atoms preferably occupy the interstitial tetrahedral-like $t$ sites comprised of four Zr atoms, with a local atomic arrangement similar to that of \ensuremath{\delta}-zirconium hydride. At higher hydrogen loadings, hydrogen atoms can also occupy octahedral-like and/or more Zr-deficient tetrahedral-like $o$ sites. The spectral differences between the as-charged and aged specimens and accompanying Vickers hardness measurements suggested that around two-thirds of the hydrogen atoms in the as-charged specimen were trapped in the strongly binding $t$ sites and relatively immobile at room temperature, while the remaining one-third occupied the more weakly binding o-sites and disappeared from the specimen upon aging. These latter sites most likely play a crucial role in the diffusion of hydrogen in BMGs at room temperature.