Basu, Saurabh
(2015)
Effect of Length Scales on Microstructure Evolution During
Severe Plastic Deformation.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Effect of length scales on microstructure evolution during Severe Plastic Deformation (SPD) was studied by machining commercial purity metals: Ni 200, Oxygen Free High Conductivity OFHC) Cu and Al 1100. By performing Orientation Imaging Microscopy (OIM) in the chips created, a switch over in microstructure evolution in small length scales was demonstrated. In this, microstructure refinement during SPD was replaced by an anomalous lack of refinement in small length scales. This switchover was found to be rampant in OFHC Cu, followed by Ni 200 but almost absent in Al 1100. It was hypothesized that the switchover is a consequence of a coupled effect of high strain gradients and small deformation volumes.
In order to quantify the switchover, flow of material in the deformation zone of machining was characterized in-situ using SEM based Digital Image Correlation (DIC). For doing this, a deformation stage capable of machining within the chamber of a Scanning Electron Microscope (SEM) was designed and fabricated. It was seen that OFHC Cu develops a sharp deformation zone during machining followed by a significantly more diffuse deformation zone in Ni 200 and then Al 1100. It was hypothesized that the switchover kicks in when the dimensions of the deformation zone approach those associated with Geometrically Necessary Boundaries
that form during SPD. Criteria for the aforementioned switchover based on this hypothesis were verified for Ni 200, OFHC Cu and Al 1100.
Effect of pre-deformation was studied by rolling Ni 200 samples prior to machining. It was seen that pre-deformation instigates the aforementioned switchover in microstructure evolution, reasons for which were discussed. A phenomenological model for predicting microstructure statistics resulting from SPD on Ni 200 in small length scales was setup. Contrary to common perception, it was shown that larger strain gradients giving rise to larger
crystallographic curvatures instigate the aforementioned switchover resulting in lack of microstructure refinement.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
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| ETD Committee: |
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| Date: |
28 January 2015 |
| Date Type: |
Publication |
| Defense Date: |
15 August 2014 |
| Approval Date: |
28 January 2015 |
| Submission Date: |
26 August 2014 |
| Access Restriction: |
5 year -- Restrict access to University of Pittsburgh for a period of 5 years. |
| Number of Pages: |
158 |
| 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: |
Length-scale effects
micro machining
Severe Plastic Deformation
Electron Back Scattered Diffraction
Digital Image Correlation
microstructure evolution |
| Date Deposited: |
28 Jan 2015 21:07 |
| Last Modified: |
28 Jan 2020 06:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/22838 |
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