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Effect of Length Scales on Microstructure Evolution During Severe Plastic Deformation

Basu, Saurabh (2015) Effect of Length Scales on Microstructure Evolution During Severe Plastic Deformation. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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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:
CreatorsEmailPitt UsernameORCID
Basu, Saurabhsab115@pitt.eduSAB115
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee MemberAcharya, Amitacharyaamit@cmu.edu
Committee MemberBidanda, Bopayabidanda@pitt.eduBIDANDA
Committee MemberWiezorek, Jorgwiezorek@pitt.eduWIEZOREK
Committee MemberChun, Youngjaeyjchun@pitt.eduYJCHUN
Committee ChairShankar, M. Raviravishm@pitt.eduRAVISHM
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: 15 Nov 2016 14:23
URI: http://d-scholarship.pitt.edu/id/eprint/22838

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