Doctoral Dissertations

Date of Award

5-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Wojciech Dmowski

Committee Members

Takeshi Egami, Yanfei Gao, Peter K. Liaw, Dayakar Penumadu

Abstract

Metallic glasses have liquid-like structure without well-defined topological defects like dislocations in metals and alloys. The unique disordered structure of metallic glasses leads to unique mechanical properties, such as inhomogeneous deformation at low temperature and homogeneous deformation at high temperature, and brittle behavior induced by annealing. This dissertation address three critical issues related to the mechanical behavior of metallic glasses:

  1. Identification of deformation defects in metallic glasses. We have conducted high energy X-ray diffraction experiment — using anisotropic pair distribution function — to characterize the size and density of defects in metallic glasses activated by external stresses. Our results based on the characterization method reveal the microscopic origin of ductility in some metallic glasses.
  2. Identification of two local stress relaxation modes that control macroscopic mechanical properties in metallic glasses. Using the defect characterization method we developed, we revealed two different local stress relaxation modes in defect regions, which are responsible for inhomogeneous and homogeneous deformation respectively.
  3. We developed structural rejuvenation method to improve and recover the compressive plasticity. The microscopic mechanism of structural rejuvenation was unveiled by structural study and molecular dynamics simulation.

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