The roles of loading rate and temperature during shear-band-to-crack transition (SCT) in bulk metallic glasses: A study of quasi-static and dynamic shearing performances at ambient and cryogenic temperatures

The concomitant of relatively ductile-like shear banding and brittle-like fracture in metallic glasses makes their failure origin, i.e., how shear bands developing into cracks, a concerned issue to reveal the unique properties of the amorphous metals. Such shear-band-to-crack transition (SCT) is prominently influenced by loading rate and temperature, whereas their roles are usually ambiguous. In this paper, serial quasi-static and dynamic tests at ambient and cryogenic temperatures were performed to clarify the roles of strain rate and temperature during SCT in a Zr-based bulk metallic glass (BMG) by an electronic testing machine and a modified split Hopkinson pressure bar (SHPB) system, respectively. Strain rates were set from 10⁻³ s⁻¹ to 10³ s⁻¹ and temperatures were set from 173 K to 293 K. In-situ and post-fracture SCT patterns have been captured by high-speed photographing and scan electronic microscopy (SEM), which show a strong relevance to shear-band decohesion. Comparisons between SCT patterns under various loading conditions have clarified that loading rate controls decohesion distribution while temperature controls decohesion resistance. A decohesion-tendency ratio of applied energy to critical decohesion resistance is established from an energy-based view, and rate and temperature dependence of the ratio is discussed to figure out how these two effects determining different decohesion behavior and subsequent SCT patterns in BMGs.