| As a new class of materials, metallic glasses (MGs) have stimulate extensive interest in the academic community, because they possess unique disordered atomic structure lacking long range translational symmetry, and thus have excellent mechanical properties. However, their deformation mechanism has not been fully understood. In this thesis, I start with an investigation of the cooling rate effect on the elastic and anelastic properties of MGs; then extend the investigation to the plastic deformation of MGs.;Quasi-static micromechanical study of the cooling-rate effect on Young's moduli and hardness of the as-cast bulks and melt-spun ribbons for a Zr-based MG was carried out. Using the nanoindentation method, Young's moduli of the ribbon samples obtained at higher cooling rates were measured which appeared to be much lower than those of the bulk samples. Through further experiments and finite-element analyses, I have clearly demonstrated that the measured difference in elastic moduli was mainly caused by the sample thickness effect in nanoindentation tests. To overcome this, microcompression were performed on the as-cast and as-spun MG samples, respectively, the results showed that the cooling rate, as ranging from ∼102 to ∼10 6 K/s, essentially has no influence on the Young's modulus and hardness of the MGs.;Then, cooling rate effect on anelastic properties of the Zr-based MGs was investigated using dynamic microcompression test. Theoretical framework based on the energy barrier concept was developed to interpret anelasticity of MG. Using this theoretical model, dynamic test results of micropillars carved out from bulk and ribbon MGs were analyzed, no discernable difference in effective modulus and viscosity can be revealed, indicating that similar content of dense packed clusters and FVZs in the bulk and ribbon MGs.;After that, the shear bands, as the plastic deformation carrier of MGs, were investigated. Important experimental finding and theoretical analysis of the shear-band speed measured in a variety of bulk MGs were presented. Based on carefully designed loading-holding cyclic tests, I revealed that the speed of a shear band correlates with its resultant shear offset. Such a correlation arises as a 'size' effect, which could be rationalized with the energy balance principle. |
