Abstract
Structural analyses of conventional amorphous alloy Zr-Ni and metallic glass Zr-Al-Ni have been studied in combination of measurements by neutron diffraction and x-ray diffraction, and their structural models have been built with the reverse-Monte Carlo method by Fukunage et al. The structural models provided us some important results. Firstly, the density of icosahedron-like polyhedra increases in the metallic glass in comparison with the conventional amorphous alloy. Secondly, the structures of amorphous alloys which include the conventional amorphous alloys as well as the metallic glasses would be characterized by the three distinct polyhedra, that is, the icosahedron-like polyhedra (I), the trigonal prism-like polyhedra (P) and the polyhedra (W) which do not belong to either. As mentioned above, the ‘ I ’ polyhedra are commonly found in the metallic glasses. The ‘ P ’ polyhedra resemble the local atomic configurations of the primary crystalline phase precipitated in the amorphous matrix. Thus, the glass formability has been determined by the competition between ‘ I ’ and ‘ P ’. The ‘ W ’ polyhedra appear in the metallic glass with increase in the fraction of ‘ I ’. They show large coordination numbers more than 13. Taking into consideration of the atomic sizes of the constituents, W is a polyhedron consisting of weakly bonded atoms in comparison with I and P. A spatial distribution of W controls the inhomogeneity of the metallic glass and is profoundly related with the fragility and other physical properties.
