Fracture behavior of Zr55Cu30Al10Ni5 bulk metallic glass under quasi-static and dynamic compression

Fracture behavior of Zr55Cu30Al10Ni5 bulk metallic glass was investigated under quasi-static compression at strain rate of 10(-4)/s using an Instron testing machine and dynamic split Hopkinson bar (SHPB) compression with strain rate of about 1900-4300/s. Pronounced strain softening, especially past the peak stress, was observed under SHPB tests and compared with the distinct flow serrations under quasi-static tests. Scanning electron microscope revealed that the angle between the loading axis and major shear plane is less than 45 degrees, deviating from the maximum shear stress plane. Microscopically, unlike the ordinary veinlike pattern found in quasi-static compression, the elongated veinlike pattern was observed at the onset position of rapid shearing under dynamic test. A closely arrayed dendritelike structure dominated the dynamic fracture, consequently, and should be the major pattern representing the rapid shear band propagation. In addition, a transition state from veinlike to dendritelike pattern was observed at the final instantaneous fracture region in quasi-static tests. Evidence revealed the characteristic dimension of dynamic fracture surface complies with Taylor's meniscus instability criterion. The roles of free volume and adiabatic heating on the fracture strength and stress concentration on the fracture morphology are also discussed.