Anelasticity-induced increase of the Al-centered local symmetry in the metallic glass La50Ni15Al35.

The mechanism of anelastic deformation of metallic glasses is a fundamental issue of materials physics. A critical step toward atomic level understanding is the identification of measurable atomic level structural parameters that respond to anelastic deformation. We demonstrate that the electric-field-gradient tensor measured by means of (27)Al nuclear magnetic resonance in glassy La50Ni15Al35 is such a parameter and it reveals that anelasticity induces atomic processes that lead to increases of local site symmetry at Al sites. Such atomic processes could play an important role in the reversible slow ß process.

Bonding characters of Al-containing bulk metallic glasses studied by 27Al NMR.

We report very small (27)Al metallic shifts in a series of Cu-Zr-Al bulk metallic glasses. This observation and the Korringa type of spin-lattice relaxation behavior suggest that s-character wavefunctions weakly participate in bonding and opens the possibility of enhanced covalency (pd hybridization) with increasing Al concentration, in good agreement with elastic constants and hardness measurements. Moreover, ab initio calculations show that this bonding character originates from the strong Al 3p band and Zr 4d band hybridization since their atomic energy levels are closer to each other while the Al 3s band is localized far below the Fermi level. This study might provide a chemical view for understanding flow and fracture mechanisms of these bulk glass-forming alloys.