Inelastic neutron scattering study of the hydrogenated (Zr55Cu30

Andrew Chihpin Chuang

¹

,

Terrence J. Udovic

²

,

Peter K. Liaw

³

et al.

Abstract

The lattice dynamics of both as-charged and room-temperature-aged, hydrogenated bulk metallic glasses (BMG's) 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 (DOS) of dissolved hydrogen atoms in the as-charged BMG shows a broad band maximized at ~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 δ-zirconium hydride. At higher hydrogen loadings, hydrogen atoms can also occupy octahedral-like and/or more Zrdeficient tetrahedral-like o-sites. The spectral differences between the as-charged and aged specimens and accompanying Vicker's 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 BMG's at room temperature.

Effect of Hydrogen Charging on Pop-in Behavior of a Zr-Based Metallic Glass

“…In the beginning of hydrogen charging, the favored or so-called trapping sites for hydrogen are those with high local potential energies, such as sites with large free volume [35], or geometrically unfavored motifs (GUMs) [36]. Hydrogen also has been found to fill interstitial sites of loosely packed Zr-rich tetrahedral-like sites (t-sites) [3,34,37,38]. These trapping sites are stabilized by the hydrogen [39], lowering the local potential energy and generally resulting in an increase in the local activation energies for atomic rearrangements, thereby restricting deformation [11].…”

Effectiveness of hydrogen microalloying in bulk metallic glass design

“…In fact, the base metals of the two BMGs studied feature different mixing enthalpies with hydrogen, where the mixing enthalpy of the Zr-H bonding pair (À69 kJ/mol [25]) is 2.5 times larger than that of Pd-H (À27 kJ/mol [25]). The strong bonding between incorporated hydrogen and the base element Zr has been verified by means of inelastic neutron scattering [46]. For small concentrations (of similar range as investigated here) the hydrogen atoms occupy tetrahedral-like sites comprised of four Zr atoms.…”