Application of in situ full-field measurement in the transmission electron microscope: Mechanical property extraction from amorphous to crystalline materials

Zhang, Yiguang

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https://hdl.handle.net/2142/121948 Copy

Description

Title

Application of in situ full-field measurement in the transmission electron microscope: Mechanical property extraction from amorphous to crystalline materials

Author(s)

Zhang, Yiguang

Issue Date

2023-10-12

Director of Research (if dissertation) or Advisor (if thesis)

• Lambros, John
• Dillon, Shen

Doctoral Committee Chair(s)

Lambros, John

Committee Member(s)

• Chasiotis, Ioannis
• Chew, Huck Beng

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• TEM loading test
• Digital Image Correlation
• Particle Tracking
• Microscale mechanical properties
• Shear yielding
• Grain boundary properties

Abstract

This thesis work develops an innovative experimental approach that combines the full-field optical measurement methods of digital image correlation (DIC) and particle tracking (PT) with an in situ loading experiment in the transmission electron microscope (TEM), and demonstrates how these full-field measurements facilitate the acquisition of microscale mechanical properties in both amorphous and crystalline materials. Central to the DIC technique is the presence of a random speckle pattern on the sample surface which can be tracked to produce measurements of surface strain and displacement during loading. The challenge of developing such a pattern suitable for use in the harsh TEM environment was solved by using a gold nanoparticle deposition technique in which a thin gold film is deposited on the sample and undergoes de-wetting upon annealing to form gold nanoparticle islands–the DIC speckles. The same speckles can also serve as markers particles for PT. The particles were seen to be effective speckles while at the same time not altering sample response. In addition to particle deposition, significant care must be taken in applying the remaining experimental procedures including sample sectioning, focused ion beam milling, TEM loading set up, and application of DIC and PT. As a demonstrator for the method, in situ TEM images were captured during a bending experiment of an amorphous SiO2 beam, and DIC and PT were applied to measure the full-field displacements. Their effectiveness was validated through a comparative analysis of these measurements. The remainder of this effort was devoted to applying the TEM/DIC/PT technique to a variety of problems in both an amorphous and a crystalline material system, SiO2 and magnesium aluminate spinel (MgAl2O4) respectively. The next part of this work delves into the electron beam irradiation induced creep (IIC) behavior of amorphous SiO2 in the TEM environment. Full-field displacements were measured from TEM images during a carefully designed multiple-ramp-loading creep experiment, and creep properties were quantified via 2D FEM parameter optimization, assuming the creep behavior was governed by Norton’s law. By determining Norton’s creep constants, the creep compliance of SiO2 was extracted, and a linear dependence between creep strain rate and stress was found. In the final part of this work, failure of single crystal and bi-crystal magnesium aluminate spinel is investigated. Due to the presence of bend contours on the crystalline sample in the TEM, rendering DIC impractical, in this case PT was used for full-field measurements. One approach in this part of work is to extract opening-dominated fracture toughness through a single-edge notched bending (SENB) test in the TEM, followed by analytical fitting with the asymptotic crack-tip field. In addition, a novel punch compression configuration is proposed to induce local shear bands, enabling an exploration of the shear yielding behavior of single crystal spinel. Through inverse analysis in the FEM, parameters for the tri-linear plasticity model were determined, thus extracting yield stress of spinel. Fracture property disparity between the grain boundary and lattice, and the mode mixity dependence of the grain boundary fracture property, were also studied. By placing a notch aligned with the grain boundary at the top or bottom edge of a bi-crystal beam sample, bending experiments can generate grain boundary failure with different mode mixites. Critical energy release rates and mode mixity indices for each sample were extracted through 3D FEM analysis, validated by PT-FEM comparisons. For opening-dominated fracture, the grain boundary exhibited a lower fracture energy compared to the single crystal lattice, providing partial evidence for nonuniform material strength of the bulk polycrystal spinel. Furthermore, different grain boundary fracture properties were observed for opening- and shear-dominated modes.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Yiguang Zhang

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