Temperature-dependent plasticity and fracture mechanism under shear loading in metallic glass

Abstract

The fracture surface morphology under shear loading is important for understanding the plasticity and the deformation mechanism of metallic glasses (MGs). However, it is difficult to carry out the shear fracture test for most MGs by conventional test methods due to their limited glass forming ability. In this work, through a unique anti-symmetrical four-point bend method, the shear fracture test is carried out under a quasi-static loading at a wide temperature range from 220 K (0.31Tg, Tg: glass transition temperature) to 620 K (0.88Tg) for a Zr-based MG. Basing on the examination on the fracture surface morphologies, we found three different fracture mechanisms with temperature: at lower temperatures (220 ~ 260 K, 0.31 ~ 0.37 Tg), both flower-like and shear-driven vein patterns appear on the fracture surface, which displays a mix of shear- and dilatation- dominated fracture; at intermediate temperatures (300 ~ 570 K, 0.42 ~ 0.80 Tg), the shear-driven vein patterns dominate on the fracture surface, indicating the shear-dominated fracture; at higher temperatures (600 ~ 620 K, >0.80 Tg), a mass of melt droplets indicate the transition from inhomogeneous to homogeneous deformation. From the Weibull statistical analysis on the main fracture features at intermediate temperatures, we found that the size of shear-driven vein patterns increases and the data distribution is sparser with the temperature increasing. The temperature dependence of fracture surface morphology as well as the relationship between the fracture surface feature and the microstructural evolution in MG were also interpreted from the shear transformation zone theory.