Yield and deformation of metallic glasses strengthened by post-extrusion addition of second phase particles

Abstract

The stress-strain behavior of metallic glasses with second phase particles was studied using a combination of scanning electron microscopy and bending tests on hairpin configurated specimens. Young's modulus and the friction stress in shear bands were derived from an analysis of the force on the platens as a function of platen distance. The addition of second phase particles of WC or TiC to the NI 75Si 8B 17 matrix increased Young's modulus and yield stress, and extended the range of plastic deformation. Young's modulus increased with the volume fraction of second phase particles in good agreement with the rule of mixture. Dispersions of WC of about 7%, almost doubled the yield strength. The increase in yield stress was analyzed with the one parameter work hardening theory of Ashby. The value derived for the friction stress agreed well with the value derived from analysis of bending in the plastic hinge regime and with previous measurements of the slip distribution in shear bands. It is argued that the friction stress is closely linked to the proportional limit; i.e. the stress level at which local rearrangements first take place in a metallic glass.