Nanomechanical studies of metallic glasses at ambient and elevated temperatures

Bulk metallic glasses, though attractive for use in structural applications for their high strength and elastic limit, display several unacceptable features upon deformation, including quasi-brittle failure along shear bands, extremely limited tensile ductility, and propensity for fatigue under cyclic loading. Though researchers have studied metallic glasses for the last fifty years, several fundamental aspects of the mechanical deformation process in these materials have not been conclusively established. In this thesis, new instrumentation and techniques were developed to study the deformation mechanism of metallic glasses, enabling a focused, high-resolution method for probing nanomechanical behavior. A nanoindenter capable of sub-nanometer and sub-microNewton resolution was outfitted with a custom heating stage and installed in a controlled atmosphere chamber to allow for high fidelity testing in a non-oxidizing environment across a range of deformation regimes. Using this system, the process of shear band initiation near a stress concentration was investigated using a low load indentation technique, revealing that high stresses at a point directly beneath the contact are not sufficient to cause shear band release to the free surface, but instead the potential for material flow along a slip line to relieve stress must be considered. Additionally, the distribution of strengths associated with the yield event was identified and its origins were determined to be mainly structural by using a variety of specially designed loading functions to examine rate, stress, and dynamic loading dependencies.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Packard, Corinne E

Advisor dc:contributor.advisor

• Christopher A. Schuh.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/46663

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/46663