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.

1.General Introduction 1.1 Motivation and Scope of Complex Materials 1.2 An Overview of Metallic Glasses 1.3 Processing of Metallic Glasses 1.4 Mechanical Property Enhancement in MG Composites 1.5 References 2. Fabrication Methods of MG Artificial Microstructures 2.1 Metallic Glass Alloy Synthesis 2.2 Silicon Mold Fabrication 2.3 Fabrication Methods of Artificial Microstructures 2.4 Conclusions 2.5 References 3. Structural Characterization of Metallic Glasses 3.1 Formability Test 3.2 Thermal Analysis 3.3 Structural Analysis 3.4 Bend Test 3.4 Conclusions 3.5 References 4. Artificial Microstructure Approach 4.1 Objectives 4.2 Periodic Cellular Structures of Metallic Glasses 4.2.1 MG Cellular Structure Sample 4.2.2 In-Plane Compression Test 4.2.3 Euler Buckling Instability 4.2.4 Results and Discussion 4.2.4.1 Deformation Regions of MG Cellular Structures 4.2.4.2 Manipulation of Geometry 4.2.4.3 Cellular Structures of Different Materials 4.2.4.4 Energy Absorption Capacity 4.2.4.5 Microstructural Optimization 4.2.4.6 Embrittlement of MGs 4.2.4.7 Comparison with Numerical Simulations 4.2.4.8 Mechanical Characterization under Uniaxial Tension 4.2.4.9 Mechanical Characterization at Different Orientations 4.2.5 General Findings & Conclusions 4.3 Toughening Mechanisms in Metallic Glasses 4.3.1 Uniaxial Tensile Test 4.3.1.1 Effect of Pore Size 4.3.1.2 Effect of Morphology 4.3.1.3 Effect of Pore Spacing 4.3.1.4 Effect of Pore Shape 4.3.1.5 Effect of Material Type 4.3.1.6 Effect of Pore Number 4.3.1.7 Effect of Electroplating 4.3.1.8 Microscopic Analysis of the Deformation Mechanism 4.3.1.9 Mechanical Property Optimization through d/s 4.3.1.10 Comparison with Numerical and Empirical Models 4.3.1.11 Effect of Isothermal Annealing on Mechanical Properties 4.3.2 Investigation of MG Composites Using FEM Analysis 4.3.3 General Findings & Conclusions 4.4 References 5. General Conclusions and Outlook 5.1 General Conclusions 116 5.2 Push the Limit: 3D Metallic Glass Structures 5.3 Multiple Material Artificial Microstructures 5.4 Non-Periodic Cellular Structures & Flaw Tolerance 5.5 Algorithmic Topological Optimization 5.6 Fracture Toughness in MG Heterostructures 5.7 Other Application Fields of MG Heterostructures 5.8 References.