Title

Bulk Metallic Glasses Structure and Properties Investigated by Scanning Probe Microscopy

Date of Award

Spring 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering & Materials Science (ENAS)

First Advisor

Schwarz, Udo

Abstract

Bulk metallic glasses (BMGs) have been intensively investigated because of their special mechanical properties as amorphous materials and their unique glass transition state. However, the atomic structural origin of their properties has not been unequivocally understood. To explain their properties, structural models of BMGs have been proposed but not yet confirmed due to the relatively macro-scale of characterization and properties measurements. Scanning probe microscopy, as one of the most advanced techniques to characterize nano to sub-nano features, possesses the potential of direct observation on the atomic structure once given a clean atomically flat surface of BMG. In this thesis, novel imprinting methods of metallic glasses that can produce atomically flat surfaces with nano to sub-nano features will be discussed. The atomic-scale imprinting is first realized via thermoplastic forming of BMGs and is then developed by magnetron sputtering of general metallic glasses. The capability of nano-imprinting at a sub-nano scale enriches the range of applications of BMGs and brings a new way to directly characterize the relaxation and crystallization performance. BMGs imprinted with sub-nano features are investigated through heat treatments with and without constraints. It can be observed from sub-angstrom to tens of nanometers surface morphology changes on the imprinted BMG when there are no surface constraints during heat treatments. But clear imprinted features can be found through crystallization takes place while the imprinted BMG is heated as pressed with molds. To realize the potential of direct characterization of the atomic structure by scanning probe microscopy, an in-situ pressing chamber is designed to facilitate thermoplastic forming in ultra-high vacuum and is attached to the main characterization system for further research.

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