Shear band deformation and fatigue striations during three-point bending fatigue crack growth in brittle metallic glass

Shear band plays a key role in fatigue damage and fracture behaviors in metallic glass (MG). The effect of the shear band on fatigue crack growth of a brittle Ti-32.8 Zr30.2Ni5.3Cu9Be22.7 (ZT3) MG with superior fatigue resistance was investigated by three-point bending fatigue testing in this work. The fatigue crack growth process is classified into three stages based on the shear band feature and crack profile. It is found that the crack path is straight and smooth with no or several shear bands near it in the former stage of fatigue crack growth, but transformed to be staircase-like with extensive shear-band proliferation in the latter stage. The transformation of crack growth path is mainly determined by three factors, i.e., the inclined shear band with respect to mode I crack plane direction, maximum energy release rate along the mode I crack plane direction and the asymmetric shear-band attribution on two sides of mode I crack plane direction. On the other hand, the fatigue fracture surface shows three regions with different fatigue striation features, which match well with three stages on the sample surface. The shear band theory including shear-band formation, propagation and cracking is utilized to well interpret the mechanism of fatigue striation formation. The present findings reveal the relation between shear band and fatigue crack growth and may provide instructions for future design of MGs with excellent fatigue resistance through controlling shear banding behavior.