Microscopic mechanism of the effect of composition and topological orders of metal glasses on plastic shear resistance

Abstract

Singularities (minima) in the critical stress of catastrophic plastic shear are observed in the course of variation of composition and topological orders in metal glasses Fe85−xCoxB15 (x=15, 17, 19, 21, 25, 30, 40, 50, 64 at. %) due to a change in the chemical composition. The minima are observed for x=21 and 40 at. %, which is close to the rational ratios 3:1 and 1:1 of atomic concentrations of Fe and Co, that are regarded as stoichiometric ratios for the formation of nanoclusters with a high average binding energy. The change in the atomic structure of cluster boundaries is considered as a microscopic mechanism of the effect of composition and topological orders on the resistance to plastic shear. The difference in the concentrations of coinciding sites at cluster boundaries is estimated for metal glasses of stoichiometric and nonstoichiometric compositions.