Doctoral Dissertations

Date of Award

5-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Peter K. Liaw

Committee Members

Yanfei Gao, Hairong Qi, Mariya Zhuravleva

Abstract

Bulk metallic glasses (BMGs) attract more and more attention for their great mechanical properties, such as high strength, good corrosion resistance, etc. However, even though extensive studies have been made, their deformation mechanisms are still not well understood. Their limited plasticity and catastrophic failure after yielding severely prevent their broad applications in industry and daily life. To improve their plasticity, some work has been done through miscellaneous processing methods, e.g., thin-film coating, surface treatment, and ion irradiation. The present work also focuses on the plastic deformation of BMGs, and is expected to deepen the fundamental understanding of the deformation mechanisms through the study of several methods, which could improve their plasticity, namely, geometrical constraint, pre-fatigue, and laser-induced constraint. To characterize the improvement, compression, four-point bending fatigue, and nanoindentation experiments were conducted. Moreover, recent work suggests that BMGs also show serrated flows in certain regimes of temperatures and strain rates, which is similar to the Portevin–Le Chatelier effect (PLC) in traditional alloys. Thus, the serrated flow can be used as a probe for studying the deformation process. Through the investigations of serration behavior, it's expected that the details of deformation dynamics can be extracted. The thermograph study and synchrotron X-ray diffraction were also utilized to investigate the shear-band dynamics and structural changes. Serration characteristics were analyzed statistically and a slip avalanche model was successfully applied on BMGs.

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