Dispersion strengthening of nanocrystalline AlTiVCr high-entropy alloys
- 주제(키워드) high-entropy alloys , multi-scale analysis , multi-phase , nanocrystalline , strengthening mechanism
- 주제(DDC) 621.042
- 발행기관 아주대학교 일반대학원
- 지도교수 Byungmin Ahn
- 발행년도 2026
- 학위수여년월 2026. 2
- 학위명 석사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000035449
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
High-entropy alloys (HEAs) have attracted attention as next-generation structural materials. The mechanical properties of HEAs vary significantly depending on their phase and microstructure. When fabricated via mechanical alloying, HEAs typically exhibit enhanced mechanical properties by a nanocrystalline microstructure. Also, when HEAs form multi-phase structure, the interactions between different phases can improve the overall mechanical properties of the alloy. In this study, nanocrystalline high-entropy alloys (HEAs) with multi-phase were fabricated by adding elements with different mixing enthalpy to induce multi-phase formation, and the correlation between the size scale of analyzing method and strengthening mechanisms was analyzed. The alloys fabricated through mechanical alloying and spark plasma sintering exhibited a nanocrystalline BCC + Laves structure. Mechanical properties were evaluated across four different scales. At the nanoscale, AFM indentation was employed to measure and compare the intrinsic mechanical properties of the individual BCC and Laves phases. The results revealed that different strengthening mechanisms dominated at each scale. Among the four alloys system, AlTiVCrFe exhibited the best overall mechanical properties. For enhancing strength, carbide dispersion strengthening was applied, and the effects of TiC content on phase evolution and mechanical behavior including ductility were examined. Increasing the TiC content led to grain refinement, an increase in the Laves phase fraction. When the TiC content exceeded a critical value, TiC agglomeration occurred instead of homogeneous dispersion. Among them, the alloy containing 1 wt.% TiC demonstrated the highest strength, along with improved ductility. This study provides a property-oriented, three-step design route that integrates thermodynamically guided multi-phase formation, multi-scale mechanical property measurement, and TiC dispersion strengthening to enhance and tune the mechanical properties of nanocrystalline AlTiVCr-based LWHEAs. The findings are expected to serve as a foundational guideline for the design of next-generation lightweight, high-strength structural materials.
more목차
Chapter 1. Introduction 1
Chapter 2. Research background 4
2. 1. High-entropy alloys (HEAs) 4
2. 1. 1. Definition and characteristics 4
2. 1. 2. Four core effects 5
2. 1. 3. Thermodynamic parameters of HEAs 8
2. 1. 4. Strength-ductility trade-off in HEAs 11
2. 2. Advanced material fabrication process, Powder metallurgy 12
2. 2. 1. Mechanical alloying 12
2. 2. 2. Sintering 14
2. 3. Property measurements at various scales 16
2. 3. 1. Limit in measuring properties of nanocrystalline multi-phase HEAs 16
2. 3. 2. Nanoscale: AFM indentation test 17
2. 3. 3. Sub-microscale: Nanoindentation test 19
2. 3. 4. Microscale: Micro-Vickers hardness test 21
2. 3. 5. Macroscale: Compression test 23
2. 4. Strengthening mechanism 25
2. 4. 1. Solid solution strengthening 25
2. 4. 2. Grain boundary strengthening 27
2. 4. 3. Work hardening 27
2. 4. 4. Precipitation strengthening 28
2. 4. 5. Dispersion strengthening 29
Chapter 3. Multi-phase formation of high-entropy alloys through mixing enthalpy control 32
3. 1. Introduction 32
3. 2. Experimental procedure 33
3. 3. Results and discussion 35
3. 3. 1. Calculated thermodynamic parameters 35
3. 3. 2. Alloying behavior of powders 37
3. 3. 3. Alloying behavior of sintered alloys 45
3. 4. Summary 59
Chapter 4. Correlation between indentation scale and strengthening mechanisms in multi-phase HEAs 60
4. 1. Introduction 60
4. 2. Experimental procedure 61
4. 3. Results and discussion 63
4. 3. 1. Nanoscale property by AFM indentation test 63
4. 3. 2. Sub-microscale property by nanoindentation test 68
4. 3. 3. Microscale property by micro-Vickers hardness test 72
4. 3. 4. Macroscale property by compression test 76
4. 3. 5. Correlation between indentation size and strengthening mechanisms 80
4. 4. Summary 85
Chapter 5. Simultaneous enhancement of strength and ductility through carbide dispersion strengthening 86
5. 1. Introduction 86
5. 2. Experimental procedure 87
5. 3. Results and discussion 90
5. 3. 1 Alloying behavior of powders 90
5. 3. 2. Alloying behavior of sintered alloys 94
5. 3. 3. Mechanical properties of sintered alloys 108
5. 4. Summary 113
Chapter 6. Overall conclusions 114
References 116
