2, Herbert Gleiter Institute of Nanoscience, Nanjing, , China
Plastic deformation of metallic glasses is mostly localized in plate-like mesoscopic defects, so-called shear bands. Their propagation often initiates catastrophic failure. Yet, small compositional variations (“minor alloying”) as well as structural heterogeneities can affect their propagation revealing different interaction mechanisms that are summarized in a qualitative mechanism map that categorizes the various processes that may occur in the course of the interaction between shear bands and structural heterogeneities.
Although the occurrence of shear bands is well known and often determines the mechanical performance of the material, their actual physical properties remain fairly unknown. Here, experimental data on the rate of atomic diffusion within shear bands have been obtained using the radiotracer method on post-deformed specimens. Additionally, novel TEM-based methods served to experimentally determine the local specific volume as well as the local degree of medium-range order and the local chemical composition quantitatively. Moreover, local strain fields at shear bands have also been analyzed and the impact of shear deformation and relaxation on the low-temperature heat capacity anomaly known as the “Boson peak” has been addressed, revealing complex dependencies on time, temperature and strain. Relaxation experiments showed an unexpected temporal evolution of the shear bands, including so-called cross-over behavior. The experimental results are discussed with respect to the underlying mechanism during the early stages of shear band activation and their temporal evolution as well as on the properties characterizing these “defects” in deformed metallic glasses.