Elucidating Deformation Mechanisms in Shape Memory Alloys Using 3D X-Ray Diffraction
Başlık:
Elucidating Deformation Mechanisms in Shape Memory Alloys Using 3D X-Ray Diffraction
Yazar:
Bucsek, Ashley, author.
ISBN:
9780355990645
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (176 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Aaron P. Stebner Committee members: Amy Clarke; Steven Decaluwe; Branden Kappes.
Özet:
Advanced materials are internationally recognized as a foundation for new capabilities, tools, and technologies that meet urgent societal needs including clean energy, human welfare, and national security. They are also recognized to be very costly to develop and slow to become commercially available, often requiring decades of research before entering the market. "Advanced materials" broadly describes innovative materials that have atypical sizes, microstructures, deformation mechanisms, and/or material responses. These atypical characteristics enable major, previously impossible technological breakthroughs, yet the previously unknown simultaneously presents new challenges to overcome in developing and certifying those technologies. To accelerate the deployment of advanced materials, major advancements in modeling and characterizing advanced materials are needed to accelerate our ability to understand and predict their behaviors.
This dissertation presents the need for, challenges of, and solutions to adapting modern X-ray diffraction experiments to elucidate the micromechanics of a subclass of advanced materials called shape memory alloys (SMAs). In particular, the previously established far-field and near-field High-Energy Diffraction Microscopy (ff-HEDM and nf-HEDM) classes of 3D X-Ray Diffraction (3DXRD) techniques and microcomputed tomography (microCT) are advanced to create new abilities to study martensitic transformations and twin reorganization in SMAs. Additionally, a recently developed technique called Dark-Field X-Ray Microscopy (DFXM), which pushes the boundaries on the length scales accessible to non-destructively evaluate crystalline materials from microns to nanometers, is used to study SMAs for the first time. This dissertation begins with an introduction to SMAs and HEDM (Chapter 1), followed by a study that illustrates the need for more complicated micromechanical modeling and associated experimental verification data sets (Chapter 2), and then goes on to report on four X-ray diffraction experiments on SMAs, where each experiment contains one or more novel approaches to experimental planning and data analysis (Chapters 3--6).
The first experiment (Chapter 3) discusses the challenges presented by the martensite phase in analyzing 3DXRD data sets for SMAs, which make analyzing the data with the traditional techniques extremely difficult or impossible. In general, these challenges may arise with any multiphase material system, especially where the crystallographic system of one or more of the phases is low symmetry (e.g., monoclinic, orthorhombic, etc.). The technique advancement used to address these challenges is to analyze the data using a forward model algorithmic approach, where the diffraction patterns of virtual microstructures are simulated and compared with the experimental diffraction patterns. In this application, the virtual microstructures are limited to those that are theoretically possible according to the Crystallographic Theory of Martensite (CTM) (also called the Phenomenological Theory of Martensite), and a work flow for the algorithmic approach is presented so that more sophisticated micromechanical models can be implemented in the future. We show that this approach is successful in identifying martensite orientations in three single crystal data sets, even when the single crystals have engineering-grade microstructure features that violate the underlying assumptions of the CTM (i.e., have precipitates, inclusions, elastic strain, subgrains, R-phase, plasticity, and are not infinite plates). We also use this implementation of the forward-model algorithm to show that the application of the widely accepted maximum transformation work criterion needs to be modified for cases where SMAs violate the assumptions of the CTM.
The second experiment (Chapter 4) presents a study where we elucidate load-induced twin rearrangement, a reversible deformation mechanism by which materials can accommodate large loads and deformations without damage through reversible rearrangements of crystallographic twins. In this in situ experiment, we use a suite of X-ray measurement probes, nf-HEDM, ff-HEDM, microCT, as well as digital image correlation (DIC). The different types of data collected are then correlated, resulting in a more complete understanding of the micromechanics as well as a variety of ways to convey both quantitative and qualitative information. We also present several data analysis techniques for the first time, including a procedure to measure subgrain-scale lattice rotation and elastic lattice strain correlations, a method to distinguish different types of regions in nf-HEDM reconstructions using confidence thresholding, and the first-ever nf-HEDM reconstruction of a monoclinic material, demonstrating the utility of nf-HEDM even for very low crystal symmetries. We show that a specific sequence of twin rearrangement micromechanisms occurs inside macroscopic deformation bands as they propagate through the microstructure, and we show that the strain localization inside these bands causes the lattice to curve by up to 15°, which has important implications on elastic strain, resolved shear stress, and maximizing the twin rearrangement.
In the third experiment (Chapter 5), we use nf-HEDM and microCT to study a phenomenon wherein both low-angle and special high-angle grain boundaries appear inside austenite grains in SMAs as a result of load-biased thermal cycling (LBTC). (Abstract shortened by ProQuest.).
Notlar:
School code: 0052
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(679565.1) | 679565-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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