Local structure of Al- and Fe-based metallic glasses

The local atomic structures of Fe- and Al-based amorphous metallic glasses have been investigated by the pair density function (PDF) analysis of neutron diffraction data. In the Fe system, chemical substitution at the transition metal ion sites induces significant changes of the local structural environment. With the substitution of Nb for Zr and Mn for Fe, a pre-peak in the structure function is observed that is indicative of short-range chemical rearrangement. This is accompanied by a reduction of volume in real space and a contraction of interatomic pair correlations that could in turn be associated with stronger glass forming ability. In the Al-Ni-Nd system, using the isotope difference neutron PDF technique, the local environments for Ni and Nd were separately determined. The Ni ions tend to form strong interactions with Al with significant shortening of the bond length and weaker interactions with Nd. The local Ni-Al cluster is almost spherical with a coordination close to twelve nearest neighbours, while Ni-Ni chemical short-range ordering is quite strong as indicated by the change of amplitude of the pre-peak with the isotopic substitution. On the other hand, the local Nd environment is more disordered with two separate Nd-Al coordination environments and weaker clustering.