PREDICTION OF AMORPHOUS FORMATION IN BINARY TRANSITION-METAL ALLOYS

An explanation of the formation of an amorphous phase in binary transition metal alloys using two band parameters (H and S) is proposed on the basis of Zunger's orbital electronegativities and the bond orbital model. It is indicated that the formation of the amorphous phase is controlled by the ratio of H to S which expresses the ionic and covalent characters, and the formability increases with increasing ratio H/S. When the ratio H/S of an AB binary alloy exceeds 1.45, the amorphous forming range can be predicted by an energy function constructed from two band parameters and the compositional factor including the valence electron number. With decreasing ratio of H to S, the predicted range of the amorphous phase deviates widely from the experimental result. The disagreement occurs because formation of the amorphous phase is not controlled predominantly by the ratio of ionic character H to covalent character S, and a different picture is required in binary alloys with ratio H/S less than 1.2.