Response of large-deformation behavior to strain rates in a bulk-metallic glass by hydrogen

Abstract

Through optimizing the technology and regulating the composition, a Zr-based bulk-metallic glass (BMG) with super-plasticity at room temperature has been successfully prepared by using copper-mold vacuum suction casting under the gaseous mixture of hydrogen and argon. The as-cast BMG sample was then processed into compression specimens with an aspect ratio of 2:1, i.e., with a size of 1 × 1 × 2 mm3. The effect of strain rates on super-plastic deformation behaviors in the BMG under uniaxial compression was systematically studied within a strain rate range from 4.2 × 10−4 s−1 to 6.0 × 10−5 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 BMG fabricated under the gaseous mixture of hydrogen and argon exhibits the super-plasticity, i.e., hydrogen addition can increase the plastic deformability of bulk-metallic glass dramatically. With the reduction of strain rate, compressive strength, elastic modulus, disproportionate stress, plastic strain, true yield stress, end stress, stress peak interval, stress fluctuation and shear band sliding interval increase, while yield strength and elastic strain reduce. The smaller the strain rate is, the higher the shear band intensity in the deformed side surfaces can be found. After yielding, the image strain-hardening is very obvious, while the real strain-softening and strain-hardening appear alternately.