Nanoscale strain mapping of metallic glass composites

Metallic glasses (MGs) are an exciting class of materials. In contrast to commonly known crystalline metals, they show a disordered structure. MGs show attractive properties making them ideal high- performance materials. Still, a major drawback of MGs is their low ductility due to localized deformation in the form of shear bands. This can lead to a sudden catastrophic fracture as observed for window-glass. Recently, it was shown that MGs containing ordered crystals show improved properties. Hence, different MG composites (MGCs) have been designed recently with enhanced plastic deformability. Experimental studies of samples after fracture show a larger number of shorter shear bands compared to MGs without crystals. Possible reasons have been found in computer simulations revealing a strong effect of the crystals on the deformation localization. It is the aim of the present project to directly observe the fundamental deformation mechanisms at the nanoscale in MGCs. To reach this challenging goal, tailored MGCs with crystals of different sizes will be synthesized using specialized casting facilities. This includes MGCs with crystals that can show a structural transformation upon deformation, thus further improving their properties. Using modern equipment, it is possible to deform nanosized samples in a transmission electron microscope, while directly observing the deformation mechanisms with nanometer resolution. In addition, the present work will develop new techniques based on diffraction with a nanosized electron beam to obtain information on the local strain and structure in the MGCs with an unprecedented spatial resolution. It is expected that the crystals have a large effect on the local strain and therefore on the deformation localization in the MGCs. The knowledge of the quantitative strains at the nanoscale will allow the comparison with computer simulations and thus facilitate the understanding and design of new composites showing improved properties. Finally, MG nanocomposites will be generated through controlled annealing of MGs with tailored structural heterogeneities. It is envisioned that the proper combination of treatments can, based on a fundamental understanding of the underlying processes and structural modifications, yield novel composites with unseen properties.