Thesis
Evaluation of strain effects on grain boundary engineering mechanisms using in situ TEM
Master of Science (M.S.), Drexel University
Jun 2013
DOI:
https://doi.org/10.17918/etd-4331
Abstract
Measurement of localized strain states on the nanoscale is of a field of interest in materials science because the information is vital to futhering the understanding of the processes of microstructural development. There are a variety of existing techniques that are capable of nano-scale strain measurement to one degree or another, however, in order to use this information in real time to inform the visualization of microstructural evolution processes such as boundary migration, an ideal technique would be one that could be carried out in a transmission electron microscope (TEM). Although techniques such as geometric phase analysis have been developed to do just that, they have limitations for some applications. For that reason, there is a demand for a new technique for the measurement of localized strain that can be carried out automaticalIy in TEM and used on a variety of sample types ranging from single crystal thin films to bulk polycrystalline materials. In this study, a technique is proposed to measure local misorientation gradients in TEM as an approximation of strain in the form of gwmetrically necessary dislocation density that is analogous to similar approaches used to treat electron backscatter diffraction data. The utility of the proposed technique is tested through its implementation in conjunction with an in situ TEM heating study on grain boundary migration and twin formation in copper. However, the mechanisms that result in the GBE microstructure are still unclear. In this study oxygen-free electronic copper was characterized in TEM both ex situ and during in situ annealing experiments in order to local strain effects on twin boundary generation and migration. The proposed strain mapping technique was used to measure local orientation gradients before and after processing. The technique was validated by comparison with visible defects as well as a comparison with geometric phase analysis (GPA). The spatial resolution of the strain maps produced was an order of magnitude larger than for GP A, showing strain values averaged across the step area, due to the spot size of the instrument used.
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Details
- Title
- Evaluation of strain effects on grain boundary engineering mechanisms using in situ TEM
- Creators
- Asher Calvin Leff - DU
- Contributors
- Mitra Taheri (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) (1970-2026); College of Engineering (1970-2026); Drexel University
- Other Identifier
- 4331; 991014632726304721