Facco, Giovanni Giuseppe
(2013)
Exploring Linear Rake Machining In 316L Austenitic Stainless Steel for Microstructure Scale-Refinement, Grain Boundary Engineering, and Surface Modification.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Thermo-mechanical processing plays an important role in materials property optimization through microstructure modification, required by demanding modern materials applications. Extreme grain size refinement, grain boundary engineering, and surface modification have been explored to establish enhanced performance properties for numerous metals and alloys in order to meet challenges associated with improving degradation resistance and increasing lifetime in harsh environments. Due to the critical role of austenitic stainless steels, such as 316L, as structural components in harsh environments, e.g. in nuclear power plants, improved degradation resistance is desirable. Linear raking, a novel two dimensional plane strain machining process, has shown promise achieving significant grain size refinement through severe plastic deformation (SPD) and imparting large strains in the surface and near surface regions of the substrate in various metals and alloys, imparting enhanced properties. Here, the effects of linear rake machining on the microstructure and related properties of 316L are investigated systematically for the first time. The controlled variation of linear raking processing parameters in combination with detailed micro-characterization using analytical electron microscopy, x-ray diffraction and associated property measurements enables the determination of the influence of changes in strain and strain rate on the developing deformation microstructure and related properties. Varying the linear raking process parameters, and consequently the strain and strain rate, affects the volume fractions of deformation induced α’-martensite and the degree of grain refinement, to the nanoscale, through SPD in the chips produced. Additionally, linear raking is identified as a way to produce surface modified structures in the specimen substrate surface of 316L, with observations of various degrees of deformation and strain up to a depth of 150m. This research clearly demonstrates that materials property modification can be achieved effectively by linear raking processing, and that resulting surface modified structures provide significant stored energy for recovery and recrystallization. This study provides a fundamental understanding of linear raking as a thermo-mechanical processing technique, which may in the future be capable of creating grain boundary engineered surface modified components for use in harsh environments like those in commercial nuclear power plants.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
25 September 2013 |
| Date Type: |
Publication |
| Defense Date: |
3 July 2013 |
| Approval Date: |
25 September 2013 |
| Submission Date: |
8 July 2013 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
137 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Materials Science and Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Thermo-mechanical processinp, TMP, Severe Plastic Deformation, SPD, Austenitic Stainless Steel, 316L, SEM, TEM, OIM, TEM-OIM, nanocrystalline, grain refinement, linear raking, 2-d plane strain machining, XRD, magnetometry, α’-martensite, surface modification |
| Date Deposited: |
25 Sep 2013 15:05 |
| Last Modified: |
15 Nov 2016 14:14 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/19277 |
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