Abolghasem, Sepideh
(2015)
Engineering of Surface Microstructure Transformations Using High Rate Severe Plastic Deformation in Machining.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
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Abstract
Engineering surface structures especially at the nanometer length-scales can enable fundamentally new multifunctional property combinations, including tunable physical, mechanical, electrochemical and biological responses. Emerging manufacturing paradigms involving Severe Plastic Deformation (SPD), for manipulating final microstructure of the surfaces are unfortunately limited by poorly elucidated process-structure-performance linkages, which are characterized by three central variables of plasticity: strain, strain-rate and temperature that determine the resulting Ultrafine Grained (UFG) microstructure. The challenge of UFG surface engineering, design and manufacturing can be overcome if and only if the mappings between the central variables and the final microstructure are delineated.
The objective of the proposed document is to first envision a phase-space, whose axes are parameterized in terms of the central variables of SPD. Then, each point can correspond to a unique microstructure, characterized by its location on this map. If the parametrization and the population of the datasets are accurately defined, then the mapping is bijective where: i) realizing microstructure designs can be reduced to simply one of tuning process parameters falling within the map\textsc{\char13}s desired subspaces. And, inversely, ii) microstructure prediction is directly possible by merely relating the measured/calculated thermomechanics at each point in the deformation zone to the corresponding spot on the maps.
However, the analytic approach to establish this map first requires extensive datasets, where the microstructures are accurately measured for a known set of strain, strain-rate and temperature of applied SPD. Although such datasets do not exist, even after the empirical data is accumulated, there is a lack of formalized statistical outlines in relating microstructural characteristic to the process parameters in order to build the mapping framework. Addressing these gaps has led to this research effort, where Large Strain Machining (LSM) is presented as a controlled test of microstructure response. Sample conditions are created using LSM in Face Centered Cubic (FCC) metals, while characterizing the deformation using Digital Image Correlation(DIC) and Infrared(IR) thermography. Microstructural consequences such as grain size, subgrain size and grain boundary responses resulting from the characterized thermomechanical conditions are examined using Electron Back-Scattered Diffraction (EBSD). Once empirical data is generated across the broad thermomechanical conditions, reliable microstructure maps are populated. This characterization can help understand surface microstructures resulting from shear-based manufacturing processes such as turning, milling, shaping, etc. that are created under analogous thermomechanical conditions.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
| Creators | Email | Pitt Username | ORCID  |
|---|
| Abolghasem, Sepideh | sea40@pitt.edu | SEA40 | |
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| ETD Committee: |
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| Date: |
11 September 2015 |
| Date Type: |
Publication |
| Defense Date: |
19 May 2015 |
| Approval Date: |
11 September 2015 |
| Submission Date: |
1 June 2015 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
136 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Industrial Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
microstructure characterization, ultrafine grain microstructure, severe plastic deformation, high speed deformation |
| Date Deposited: |
11 Sep 2015 17:51 |
| Last Modified: |
15 Nov 2016 14:28 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/25298 |
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