Microstructure-Property Optimization in Metallic Glasses

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 independently and systematically analyzed. The author evaluates and optimizes the elastic and plastic deformation, as well as the overall toughness of cellular honeycombs under in-plane compression and porous heterostructures under uniaxial tension. The study reveals three major deformation zones in cellular metallic glass structures, where deformation changes from collective buckling showing non-linear 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. The author 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.

Dr. Baran Sarac received his B.S. degree in metallurgical and materials engineering and mechanical engineering from Middle East Technical University, Ankara, Turkey. He has completed his masters and doctorate degree in the Department of Mechanical Engineering and Materials Science at Yale University, New Haven, CT, under the mentorship of Prof. Jan Schroers. He worked successively as a postdoctorate researcher in Helmholtz Zentrum Geesthacht for one year, and has recently embarked on his new position at Leibniz Institute, IFW Dresden with the same title on mechanical and functional characterization of smart alloy systems. His other research interests include structural design, thermoplastic forming, in-situ testing and morphological characterization of advanced cellular structures, as well as numerical simulations of superplastic materials via finite element analysis. Through his studies at Yale University, Dr. Sarac has been entitled to several esteemed awards, including 2013 Yale University Harding Bliss Prize owing to his contributions to further the intellectual life of the Yale School of Engineering & Applied Science, Pierre W. Hoge fellowship (between 2008-2009), and 2012 Materials Research Society Fall Best Poster Award. His publications have appeared in peer reviewed international journals such as Nature Communications, Advanced Functional Materials, Acta Materialia, Materials Letters, Scripta Materialia, and Journal of Microelectromechanical systems (IEEE), where he was concomitantly involved in federal research projects of DARPA and US Department of Energy.

General Introduction.- Fabrication Methods of MG Artificial Microstructures.- Structural Characterization of Metallic Glasses.- Artificial Microstructure Approach.- General Conclusions and Outlook.