Shear banding mode transformation induced strong strain delocalization in amorphous CuTa alloy with nanolayered structure

Metallic glasses possess ultra-high strength but negligible plasticity due to the shear banding induced strong strain localization. A feasible route to alleviate the strength-plasticity dilemma is to introducing amorphous/amorphous interfaces (A/AIs) to suppress the strain localization. However, the existing studies are mainly focused on the heterogeneous A/AIs that are made by different material systems in different constituent layers. In this paper, a new route has been proposed to suppress the shear banding induced strain localization of amorphous materials by introducing a high density of homogeneous A/AIs in an amorphous CuTa alloy. The homogeneous A/AIs are produced by varying the elemental concentration of Cu and Ta in the neighboring CuTa layers to form a CuTa/CuTa nanolayered glass (NLG) structure. The layer thickness dependent (h varies from 100 to 5 nm) strengthening and shear banding behavior of the CuTa NLGs were systematically investigated by nano/micro-indentations and the development of a theoretical model to quantify the shear banding induced strain localization. The indented deformation was discovered to transform from a few intense clockwise-kinking mediated severe cutting-like shear bands that produce a maximum effective strain of 2.21 at large h to a large amount of slight counter-clockwise-kinking accommodated minor ones with an order of magnitude lower effective strain (0.49) at small h, in which the latter leads to a complete elimination of the macro shear banding in the indented surface. The above shear banding mode transition is attributed to the competition between the flow stress of the layered structure and the intra-layer shear band nucleation stress. The present work provides a simple way for designing strong and ductile amorphous materials by architecting homogeneous A/AIs to achieve strong strain delocalization in nanoscale.