Shear-band cavities and strain hardening in a metallic glass revealed with phase-contrast x-ray tomography

Using high-energy x-ray tomography we show that deformed Zr-based metallic-glass samples contain large amounts of shear-band cavities (internal cracks). Since the investigated samples were unloaded prior to fracture, the three-dimensionally reconstructed samples can be used to determine the true load-bearing area, which leads to the conclusion that the samples have hardened considerably during deformation. We propose how such apparent strain hardening can be caused by a change in friction condition between the detached surfaces instead of searching for an intrinsic hardening mechanism. These results indicate the importance of knowing the true load-bearing area for correct flow-stress determinations of metallic glasses.