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Investigation of Phase Stability of FCC High Entropy Alloy under Extreme Environment : 극한 환경 하에서 FCC 하이엔트로피 합금의 상 안정성 고찰
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | 박은수 | - |
| dc.contributor.author | 김진연 | - |
| dc.date.accessioned | 2018-11-12T00:57:51Z | - |
| dc.date.available | 2018-11-12T00:57:51Z | - |
| dc.date.issued | 2018-08 | - |
| dc.identifier.other | 000000153332 | - |
| dc.identifier.uri | https://hdl.handle.net/10371/143169 | - |
| dc.description | 학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2018. 8. 박은수. | - |
| dc.description.abstract | Unlike conventional alloy such as steels, high entropy alloy (HEA) consists of multiple elements with similar atomic percentage and shows solid solution with various atomic environment. Due to enhanced phase stability of the HEAs, they have been paid significantly attention among the multi-component system. The HEAs show stable solid solution, sluggish diffusion and lattice distortion effects, and consequently they exhibit excellent mechanical properties at cryogenic as well as elevated temperature and improved radiation resistance | - |
| dc.description.tableofcontents | Chapter 1. Introduction 1
1.1 Radiation Effects on Materials 4 1.2 Irradiation Environment Variables 9 1.2.1 Incident Particle Type 9 1.2.2 Irradiation Temperature 16 1.3 Development of Nuclear Materials 19 1.4 Core Effects of High Entropy Alloy 28 1.4.1 High Entropy Effect 28 1.4.1 Lattice Distortion Effect 30 1.4.2 Sluggish Diffusion Effect 38 Chapter 2. Experimental Procedure 46 2.1 Sample preparation 46 2.1.1 Casting and Post Processing 46 2.1.2 TEM Sample Preparation 49 2.1.3 Sub-micron Pillar Fabrication 51 2.2 Microstructural Characterization 53 2.2.1 X-ray Diffraction 53 2.2.2 EPMA & SEM 53 2.2.3 (S)TEM & TEM holder 54 2.2.4 Orientation Mapping using PED 56 2.2.5 STEM-EDS tomography 56 2.2.6 Atom Probe Tomography 58 2.3 Thermal Analysis 60 2.3.1 Laser Flash Method 60 2.4 Mechanical Analysis 62 2.4.1 Indentation Test 62 2.4.2 Nano-pillar Compression Test 62 2.5 Irradiation Experiment 64 2.5.1 HVEM 64 2.5.2 2 MV Tandem Accelerator 66 Chapter 3. Precipitation during Solidification and Annealing and Its Effect on the Mechanical Responses 68 3.1 Introduction 68 3.2 Solidified Microstructure 74 3.2.1 Hierarchical Microstructure Analysis 74 3.2.2 Three Dimensional Microstructural Characterization 81 3.3 Solidification Sequence 87 3.3.1 Calculation and Reliability of Pseudo-binary Phase Diagram 87 3.3.2 Origin of the 2nd Phase Formation upon Solidification 89 3.4 Microstructural Evolution upon Annealing 90 3.4.1 Multi-scale Microstructure Characterization 90 3.4.2 Precipitation Evolution upon Annealing 100 3.5 Mechanical Responses of Solidified and Annealed CrFeCoNiCu HEA 104 3.5.1 The Role of Precipitation on Mechanical Property 104 3.5.2 Composite Effect on Mechanical Property 111 3.6 Summary 115 Chapter 4. Kinetics of Defect Clusters upon MV Electron Irradiation 118 4.1 Introduction 118 4.2 Environments for Electron Irradiation 119 4.2.1 Dose Calculation 119 4.2.2 Beam Heating Effect 120 4.3 Evolution of Defect Clusters 124 4.3.1 Type and Density of Defect Clusters 124 4.4 Growth of Defect Clusters 134 4.5 Lifetime of Defect Clusters 138 4.6 Evolution of Defect Clusters at Elevated Temperature 141 4.7 Summary 145 Chapter 5. Direct Observation of Irradiation-induced Polygonization and Dynamic Recrystallization 147 5.1 Introduction 147 5.2 Irradiation Condition and Dose Calculation 148 5.3 Microstructural Evolution of Ion-irradiated CrFeCoNiCu HEA 154 5.3.1 Surface Morphology 154 5.3.2 Quantified Irradiation-induced Polygonization and Recrystallization near Surface using PED 158 5.3.3 Mechanism for Suppressed Irradiation-induced Polygonization and Recrystallization in HEA 164 5.4 Summary 171 Chapter 6. Phase stability in CrFeCoNiCu HEA upon Ion Irradiation 174 6.1 Introduction 174 6.2 Irradiation Condition and Analysis from APT Data 177 6.2.1 Irradiation Condition and Dose Rate Calculation 177 6.2.2 Precipitate Characterization via APT analysis 177 6.2.3 Classification of Region in Irradiated Alloy 179 6.3 Precipitation Shrinkage and Dissolution under Ion Irradiation 182 6.4 Determination of Effective Temperature 189 6.5 Ostwald Ripening under Irradiation 193 6.6 Phase Stability under Irradiation: Competition between Radiation-enhanced Diffusion and Ballistic Diffusion 197 6.7 Applicability of HEA as Nuclear Materials 200 6.8 Summary 204 Chapter 7. Outlook and Conclusion Remarks 205 Bibliography 211 Abstract in Korean 219 Acknowledgements 223 | - |
| dc.language.iso | en | - |
| dc.publisher | 서울대학교 대학원 | - |
| dc.subject.ddc | 620.1 | - |
| dc.title | Investigation of Phase Stability of FCC High Entropy Alloy under Extreme Environment | - |
| dc.title.alternative | 극한 환경 하에서 FCC 하이엔트로피 합금의 상 안정성 고찰 | - |
| dc.type | Thesis | - |
| dc.description.degree | Doctor | - |
| dc.contributor.affiliation | 공과대학 재료공학부 | - |
| dc.date.awarded | 2018-08 | - |
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