UNIVERSITY OF CALIFORNIA SAN DIEGO Multiscale Characterization Techniques to Elucidate Mechanical Behavior of Materials A dissertation submitted in partial satisfaction of the Requirements for the degree Doctor of Philosophy in Materials Science and Engineering by Chaoyi Zhu Committee in charge Kenneth S. Vecchio, Chair Jian Luo Vlado Lubarda Jeffrey S. Gee Emily Joyce Van Allen 2019 SIGNATURE PAGE The Dissertation of Chaoyi Zhu is approved, and it is acceptable in quality and form for publication and electronically: Chair University of California San Diego 2019 iii DEDICATION In recognition of the guidance and support he has provided over the past four years, this dissertation is dedicated to my advisor, Dr. Kenneth Vecchio. Besides, in recognition of all the love and support they have given me in pursuing my passion, this dissertation is dedicated to my parents Weimin Zhu and Youzhen Xu, and my wife Yidan Hu. iv TABLE OF CONTENTS Contents SIGNATURE PAGE ...................................................................................................................... iii DEDICATION ............................................................................................................................... iv TABLE OF CONTENTS ................................................................................................................ v LIST OF ABBREVIATIONS ....................................................................................................... xii LIST OF FIGURES ..................................................................................................................... xiii LIST OF TABLES ..................................................................................................................... xxiv ACKNOWLEDGEMENT .......................................................................................................... xxv VITA ......................................................................................................................................... xxvii ABSTRACT OF DISSERTATION ............................................................................................. xxx Chapter 1 Introduction .................................................................................................................... 1 1.1 Motivation ........................................................................................................................... 1 1.2 Scanning Electron Microscope (SEM) ............................................................................... 2 1.3 Electron Backscatter Diffraction ......................................................................................... 6 1.3.1 Fundamentals of Electron Diffraction Physics ................................................................... 7 1.3.2 Automated Indexing of Electron Backscatter Diffraction Pattern ...................................... 9 1.3.3 Strain and Lattice Rotation ............................................................................................... 13 1.4 Geometrically Necessary Dislocations and Statistically Stored Dislocation .................... 18 1.5 Digital Image Correlation ................................................................................................. 20 v 1.6 Research Objectives and Outline of Dissertation ............................................................. 21 Reference ...................................................................................................................................... 22 Chapter 2 Determination of Geometrically Necessary Dislocations in Large Shear Strain Localization in Aluminum ............................................................................................................ 28 Abstract ......................................................................................................................................... 28 Nomenclature ................................................................................................................................ 29 2.1 Introduction ....................................................................................................................... 30 2.2 Experimental ..................................................................................................................... 32 2.2.1 Materials ........................................................................................................................... 32 2.2.2 Design of CFSS samples from Al-7039 plate ................................................................... 32 2.2.3 Metallographic analysis .................................................................................................... 33 2.3 GND Density Analysis ...................................................................................................... 34 2.3.1 Theory ............................................................................................................................... 34 2.3.2 Minimization Schemes...................................................................................................... 39 2.3.3 GND Resolution Determination ....................................................................................... 40 2.3.4 Step Size Dependence Analysis ........................................................................................ 41 2.3.5 Line-Averaged GND Density Profile (for simple shear experiment) ............................... 42 2.4 Results and Discussion ..................................................................................................... 43 2.4.1 Mechanical response of the materials ............................................................................... 43 2.4.2 Morphological anisotropy ................................................................................................. 46 vi 2.5 Conclusions ....................................................................................................................... 58 Acknowledgements ....................................................................................................................... 60 Reference ...................................................................................................................................... 60 Chapter 3 Investigation of the shear response and geometrically necessary dislocation densities in shear localization in high-purity titanium ..................................................................................... 66 Abstract ......................................................................................................................................... 66 Nomenclature ................................................................................................................................ 67 3.1 Introduction ....................................................................................................................... 67 3.2 Experimental ..................................................................................................................... 70 3.2.1 Materials ........................................................................................................................... 70 3.2.2 Design of CFSS samples from high purity Ti ................................................................... 71 3.2.3 Experimental Details ......................................................................................................... 72 3.2.4 Metallographic analysis .................................................................................................... 73 3.3 GND density Calculation .................................................................................................. 74 3.4 Line-averaged GND density profile (for simple shear experiment) ................................. 78 3.5 Results and Discussion ..................................................................................................... 79 3.5.1 Mechanical response of the materials ............................................................................... 79 3.5.2 Shear Damage Evolution – Post Mortem Optical Microscopy ......................................... 81 3.5.3 GND Density Calculation-Crystallographic anisotropy ................................................... 82 3.6 Conclusions ....................................................................................................................... 90 vii Acknowledgements ....................................................................................................................... 92 Appendix ....................................................................................................................................... 92 Reference ...................................................................................................................................... 93 Chapter 4 Dislocation-type evolution in quasi-statically compressed polycrystalline nickel ...... 99 Abstract ......................................................................................................................................... 99 Nomenclature .............................................................................................................................. 100 4.1 Introduction ..................................................................................................................... 100 4.2 Experimental ..................................................................................................................