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Phase Transformation and Alloying Behavior of AlCoCrFeNiX (X=Cu, Mg, Mn, Ti, Zn) High Entropy Alloys
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | 안병민 | - |
| dc.contributor.author | Oh, Minchul | - |
| dc.date.accessioned | 2018-11-08T08:28:02Z | - |
| dc.date.available | 2018-11-08T08:28:02Z | - |
| dc.date.issued | 2018-08 | - |
| dc.identifier.other | 28151 | - |
| dc.identifier.uri | https://dspace.ajou.ac.kr/handle/2018.oak/14032 | - |
| dc.description | 학위논문(박사)--아주대학교 일반대학원 :에너지시스템학과,2018. 8 | - |
| dc.description.tableofcontents | Table of Contents Abstract i Table of Contents iv List of Figures vii List of Tables xi Chapter Ⅰ. Introduction 1 Chapter II. Research background 6 II.1. High entropy alloys 6 II.1.1. Characteristics 8 II.1.2. Effects of alloying elements 12 II.1.3. Valance electron concentration 18 II.1.4. Fabrication methods 20 II.2. Mechanical alloying with milling process 23 II.2.1. Processing variables 25 II.2.2. Mechanisms of alloying 30 II.2.3. Mechanical alloying and milling processing 32 II.2.4. Effects of components on the cold welding and fracturing 36 II.2.5. Powder characterizations 38 II.3. Spark plasma sintering 42 II.3.1. Basic configuration 43 II.3.2. Principles 45 II.3.3. Mechanisms of processing 46 II.4. Nano-indentation 49 Chapter III. Alloying behavior of high entropy alloys depending on milling processes 51 III.1. Introduction 51 III.2. Experimental procedures 52 III.3. High energy milling 56 III.4. Cryomilling 68 III.5. Comparisons 77 Chapter IV. Phase transformation behavior of high entropy alloys with valance electron concentration 79 IV.1. Introduction 79 IV.2. Experimental procedures 80 IV.3. High entropy alloys with BCC structure 82 IV.4. High entropy alloys forming sigma phase 97 IV.5. High entropy alloys forming dual phase 112 IV.6. Comparisons 126 Chapter Ｖ. Mechanical behavior of high entropy alloys according to phase separation 128 V.1. Introduction 128 V.2. Experimental procedures 129 V.3. Micro-mechanical properties 131 V.4. Nano-mechanical properties 138 V.5. Comparisons 147 Chapter VI. Conclusions 149 References 152 | - |
| dc.language.iso | eng | - |
| dc.publisher | The Graduate School, Ajou University | - |
| dc.rights | 아주대학교 논문은 저작권에 의해 보호받습니다. | - |
| dc.title | Phase Transformation and Alloying Behavior of AlCoCrFeNiX (X=Cu, Mg, Mn, Ti, Zn) High Entropy Alloys | - |
| dc.title.alternative | Min Chul Oh | - |
| dc.type | Thesis | - |
| dc.contributor.affiliation | 아주대학교 일반대학원 | - |
| dc.contributor.alternativeName | Min Chul Oh | - |
| dc.contributor.department | 일반대학원 에너지시스템학과 | - |
| dc.date.awarded | 2018. 8 | - |
| dc.description.degree | Master | - |
| dc.identifier.localId | 887542 | - |
| dc.identifier.uci | I804:41038-000000028151 | - |
| dc.identifier.url | http://dcoll.ajou.ac.kr:9080/dcollection/common/orgView/000000028151 | - |
| dc.subject.keyword | High entropy alloys(HEAs) | - |
| dc.subject.keyword | Cryomilling | - |
| dc.subject.keyword | High energy milling | - |
| dc.subject.keyword | Alloying behavior | - |
| dc.subject.keyword | Phase transformation | - |
| dc.description.alternativeAbstract | High entropy alloys(HEAs) alloyed with more than five elements at equivalent atomic ratios have a high entropy effect, a lattice distortion effect, a sluggish diffusion effect, and a cocktail effect due to the complex interaction of the elements. As a result, it has better mechanical, electrical and thermal properties than commercial alloys. A lot of research has been published as a new concept material that can replace various conventional structural materials. Recently, HEAs are generally produced by arc melting casting, which may cause shrinkage defects, dendrite, and segregation in the casting process. Therefore, it are required multi-layer melting and solidification process. In order to solve the problems, research on newly HEAs fabricated by powder metallurgy process is needed. So, we investigate the phase transformation and separation of HEAs using mechanical alloying, and develop a new HEAs with high mechanical properties. In order to establish optimal alloying process conditions, AlCoCrFeNiTi powders mixed in equivalent element ratio and then alloyed with high energy milling and cryomilling respectively. Alloyed powders were densified by spark plasma sintering(SPS). Also, phase separation and transformation behavior were analyzed. Also, to investigate the phase transformation behavior and mechanical properties of HEAs according to the additive elements, HEAs was alloyed with Cu, Mn, Mg, Ti or Zn to AlCoCrFeNi by high energy milling process. After densification, microstructural changes according to process steps and additive elements were compared and analyzed. The phase transformation behavior on HEAs was studied. As the valance electron concentration(VEC) of the HEAs increases, the fraction of the face centered cubic(FCC) phase growth. Also, AlCoCrFeNi and AlCoCrFeNiMn with body centered cubic(BCC) and FCC formed a fine sigma phase Cr and Fe rich phase, due to lower the energy level in matrix. The change of the mechanical properties according to the additive element is researched, Cu forms a nano scale liquid phase during the densification process. Ti has a higher hardness and a lower lattice constant than other elements so that alloying does not occur well during high energy milling and densification processes, by the reason, the nano scale Ti phase is distributed in the grain boundaries. Mg and Zn form pores due to vaporization. Pore and rich phase induced deterioration of mechanical properties on HEAs. On the other hand, Mn is a simple cubic structure, and its diffusion rate is speedy due to the large lattice constant. So, alloying, phase stabilization and separation quickly were occurred during mechanical alloying and densification processes. For a reason, fine ordered BCC and sigma phase are formed. Finally, HEAs with excellent mechanical properties were fabricated in this study. In this study, various HEAs which have not been studied were fabricated with the mechanical alloying process. Also, the optimal process conditions for successfully producing HEAs using high energy milling and cryomilling were established. And, the phase transformation, separation behavior and microstructural changes of HEAs were investigated according to the added elements. The relationship between microstructure and mechanical properties was investigated. It is expected to be applied to various research including high-strength light-weight HEAs based on Al, Ti and Mg and low cost HEAs based on Al, Mg, and Zn. Also, the optimal mechanical alloying condition which is established in this study can be applied to various powder metallurgy processes. | - |
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