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Springer Theses Recognizing Outstanding Ph.D. Research Springer Theses – the “best of the best” Internationally top-ranked research institutes select their best thesis annually for publication in this series. Nominated and endorsed by two recognized specialists, each thesis is chosen for its scientific excellence and impact on research. For greater accessibility to non-specialists, the published versions include an extended introduction, as well as a foreword by the student’s supervisor explaining the special rel- evance of the work for the field. As a whole, the series provides a valuable resource both for newcomers to the relevant field, and for other scientists seeking detailed background information on special questions. Finally, it provides an accredited documentation of the valuable contributions made by today’s younger generation of scientists. The content of the series is available to millions of readers worldwide and, in addi- tion to profiting from this broad dissemination, the author of each thesis is rewarded with a cash prize equivalent to € 500. More information about this series at http://www.springer.com/series/8790 Baran Sarac Microstructure-Property Optimization in Metallic Glasses 1 3 Baran Sarac Institute für Complex Materials Leibniz Institute IFW Dresden Dresden Germany ISSN 2190-5053 ISSN 2190-5061 (electronic) Springer Theses ISBN 978-3-319-13032-3 ISBN 978-3-319-13033-0 (eBook) DOI 10.1007/978-3-319-13033-0 Library of Congress Control Number: 2014958305 Springer Cham Heidelberg New York Dordrecht London © Springer International Publishing Switzerland 2015 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Foreword This thesis consists of an in-depth study of investigating microstructure–property relationships in bulk metallic glasses using a novel quantitative approach by which influence of the second phase features on mechanical properties can be indepen- dently and systematically analyzed. We adopted this strategy to evaluate and optimize the elastic and plastic deformation, as well as the overall toughness of cellular honeycombs under in-plane compression and porous heterostructures under uniaxi- al tension. The first study revealed three major deformation zones in cellular metallic glass structures, where deformation changes from collective buckling showing nonlinear elasticity to localized failure exhibiting a brittle-like deformation, and finally to global sudden failure with negligible plasticity as the length to thickness ratio of the ligaments increases. For the second case, it has been found that spacing and size of the pores, the pore configuration within the matrix, and the overall width of the sample determines the extent of deformation, where the optimized values are attained for pore diameter to spacing ratio of one with AB-type pore stacking. In general, this versatile concept can also provide an insight to a wide range of problems including very complicated microstructural architectures, stochastic foam designs found in nature, as well as flaw tolerance and sensitivity studies of different classes of materials. Yale University, Department of Prof. Jan Schroers Mechanical Engineering and Materials Science (Supervisor of Dr. Baran Sarac) v Acknowledgements I take this opportunity to extend my gratitude to the people who have been instru- mental in the successful completion of this thesis. I would like to express my deep- est appreciation to my advisor, Prof. Jan Schroers, who has been abundantly helpful and has offered invaluable assistance and support. He is not only a successful scien- tist, but also a role model for the young scientists of our generation with his energy and dedication to his work. I will forever value our scientific discussions, and will always be inspired by his vision and perception of life. I take immense pleasure in thanking Prof. Corey S. O’Hern and Prof. Aaron M. Dollar for serving on my advisory committee and providing me guidance and feedback on my thesis research. I would like to show my greatest appreciation to my external committee member, Prof. Robert D. Conner. I am also grateful to my former committee member, Prof. Ainissa G. Ramirez for her contributions and support in my special investigations and my area exam. I would also like to express my gratitude to Prof. John B. Morrell who acted as a committee member in my disserta- tion progress presentations. Many thanks to our former postdoc, Dr. Golden Kumar, who has recently be- come a professor at Texas Technical University, for his vast contributions and his insightful comments about my research throughout my PhD. I would like to thank Prof. Jamie Guest at Johns Hopkins University, who uti- lized computational algorithm to structurally optimize cellular structures. Special thanks to Dr. Amish Desai for providing me silicon templates and contributing to the revision of my paper about blow-molding of metallic glasses. I also thank A.J. Barnes, who sent me superplastically formable aluminum alloy pieces to generate heterostructures. I would like to thank all of the undergraduate researchers who have worked/been working in my research projects and providing me experimental data. I owe thanks to my current and previous colleagues, friends, as well as many other people in our department and school, for their valuable ideas, support and assistance throughout my PhD study. Finally, yet importantly, I would like to express my heartfelt thanks to my be- loved parents, Nes’e Sarac and Prof. A. Sezai Sarac, for their blessings and guidance. vii Article Note (Parts of this Thesis) Parts of this thesis have been published in the following journal articles: • Sarac, B., Schroers, J., “Designing Tensile Ductility in Metallic Glasses”, Nature Communications, 06/2013, vol. 4, pp. 1–7, DOI: 10.1038/ncomms3158. • Sarac, B., Schroers, J., “From brittle to ductile: Density optimization of Zr- based bulk metallic glass cellular structures”, Scripta Materialia, 06/2013, vol. 68, pp. 921–924, DOI: 10.1016/j.scriptamat.2013.02.030. • Sarac, B., Ketkaew, J., Popnoe, D. O. and Schroers, J., “Honeycomb Structures of Bulk Metallic Glasses”, Advanced Functional Materials, 04/2012, vol. 22, pp. 3161–3169, DOI: 10.1002/ adfm.201200539. • Sarac, B., Kumar, G., Hodges, T., Ding, S., Desai, A., and Schroers, J., “Three- Dimensional Shell Fabrication Using Blow Molding of Bulk Metallic Glass”, Journal of Microelectromechanical Systems, 02/2011, vol. 20, pp. 28–36, DOI: 10.1109/JMEMS.2010.2090495. ix Contents 1 General Introduction ................................................................................ 1 1.1 Motivation and Scope of Complex Materials .................................... 1 1.2 A n Overview of Metallic Glasses (MGs) ........................................... 3 1.3 Processing of MGs ............................................................................. 5 1.4 Mechanical Property Enhancement in MG Composites .................... 10 References ................................................................................................... 12 2 Fabrication Methods of Artificial Microstructures ............................... 17 2.1 M etallic Glass (MG) Alloy Synthesis ................................................ 17 2.2 S ilicon Mold Fabrication ................................................................... 18 2.3 Fabrication Methods of MG Artificial Microstructures ..................... 19 Conclusions ................................................................................................. 24 References ................................................................................................... 28 3 Structural Characterization of Metallic Glasses .................................... 29 3.1 Formability Test ................................................................................. 29 3.2 Thermal Analysis ............................................................................... 30 3.3 Structural Analysis ............................................................................. 31 3.4 Bend Test ............................................................................................ 34 Conclusions ................................................................................................. 35 References ................................................................................................... 36 4 Artificial Microstructure Approach ........................................................ 37 4.1 Objectives .......................................................................................... 37 4.2 Periodic Cellular Structures of MGs .................................................. 38 4.2.1 M G Cellular Structure Sample ............................................... 39 4.2.2 In-Plane Compression Test .................................................... 40 4.2.3 Euler Buckling Instability ...................................................... 41 4.2.4 Results and Discussion .......................................................... 42 4.2.5 General Findings and Conclusions ........................................ 59 xi xii Contents 4.3 T oughening Mechanisms in MGs ...................................................... 60 4.3.1 U niaxial Tensile Test .............................................................. 61 4.3.2 I nvestigation of MG Composites Using FEM Analysis ........ 72 4.3.3 G eneral Findings and Conclusions ........................................ 75 References ................................................................................................... 77 5 General Conclusions and Outlook ........................................................... 81 5.1 General Conclusions .......................................................................... 81 5.2 P ush the Limit: 3D Metallic Glass Structures .................................... 82 5.3 M ultiple Material Artificial Microstructures ..................................... 83 5.4 N onperiodic Cellular Structures and Flaw Tolerance ........................ 85 5.5 Algorithmic Topological Optimization .............................................. 86 5.6 F racture Toughness in MG Heterostructures ..................................... 86 5.7 O ther Application Fields of MG Heterostructures ............................. 87 References ................................................................................................... 88 Index ................................................................................................................. 89