Mechanical Behaviors of Crystalline-Amorphous Nanolaminates

Amorphous alloys (also referred to as metallic glasses) demonstrate superior mechanical strength, elastic limit and wear resistance. However, macroscopically the ductility of amorphous alloys is very limited, hindering their applications as structural materials. After plastic yielding, formation and rapid propagation of shear bands leads to shear localization and softening before catastrophic failure. By introduction of crystalline phases into amorphous matrix, metallic glass composites show improved ductility and plasticity. This thesis focuses on the deformation behaviors of metallic glass composites at nanoscale: crystalline/amorphous multilayered thin films. Systematic nanoindentation tests reveal the unusual size dependent strengthening mechanisms. Furthermore, tensile tests of crystalline/amorphous multilayers on polymer substrate demonstrate that ductile dimples can be achieved in metallic glass after fracture by optimizing size and interface. Nanoscratch tests show that instability of metallic glasses arising from shear band formation can be inhibited by the constraint of crystalline phases, and the friction behavior of crystalline/amorphous multilayers depends on layer thickness. In addition, via in situ micropillar compression technique, strategies to suppress shear instability of metallic glasses are demonstrated. This research provides valuable insight to enhance plasticity of metallic glasses through size and interface