Effect of aspect-ratio alterations on plastic-deformation-behavior of a large-plastic bulk metallic glass

Abstract

Because very limited plastic strain can be developed in bulk metallic glasses (BMGs) before failure under uniaxial loading, the plastic-flow behavior is difficult to investigate. In present paper, through optimizing preparation processes and regulating alloy composition, we prepared a 3 mm-in-diameter Zr-based BMG rod with superplasticity at room temperature by using copper-mold vacuum suction casting. The effect of specimen’s aspect ratios on room-temperature superplastic deformation behavior in the BMG under uniaxial compression was studied at a strain rate of 4.2 × 10−4 s−1. The results showed that there is no sign of fracturing after the BMG specimens have suffered from a nominal strain of 85.5%, i.e., a true strain of 193.1%, indicating the superplasticity of the BMG. With the increase of aspect ratio, compressive strength, plastic strain, true yield stress, end stress and stress fluctuation increase, while elastic modulus, disproportionate stress, stress peak interval, yield strength, elastic strain and shear band sliding interval reduce. The higher the aspect ratios, the larger the densities of shear bands in the deformed side surfaces. During the plastic flow, the pseudo strain-hardening effect becomes more obvious with the increasing aspect ratios, while the real strain-softening effect becomes more serious with the descending aspect ratios.