표제지
목차
국문요약 12
제1장 서론 14
제2장 이론적 배경 19
2.1. 고엔트로피 합금 19
2.1.1. 고엔트로피 합금의 정의 19
2.1.2. 고엔트로피 합금의 핵심효과 24
2.1.3. bcc 계 고엔트로피 합금 29
2.2. 금속의 강화기구 33
2.2.1. 고용 강화 (Solid-solution hardening) 33
2.2.2. 결정립 미세화 강화 (Grain refinement strengthening) 35
2.2.3. 석출 강화 (Precipitation strengthening) 37
제3장 실험방법 39
3.1. TiVZrNb계 합금 제조 39
3.1.1. 합금의 제조 39
3.1.2. 균질화 열처리 41
3.1.3. 냉간 압연 및 재결정화 43
3.2. 미세조직 및 상 분석 45
3.2.1. 전계 방사 주자전자현미경 분석(FE-SEM) 45
3.2.2. X-선 회절 분석(XRD) 45
3.2.3. 밀도 측정 46
3.3. 기계적 특성 평가 48
3.3.1. 경도 측정 48
3.3.2. 압축 및 인장 시험 50
3.4. X선 회절 패턴 분석을 통한 격자 변형률 측정 52
3.4.1. 원자쌍분포함수(Pair Distribution Function, PDF) 52
3.4.2. 원자쌍분포함수를 이용한 단주기에서의 격자 변형률 측정 53
제4장 결과 및 고찰 56
4.1. TiVZrNb계 합금 설계 56
4.2. TiVZrNb계 경량 고엔트로피 합금 미세 조직 및 상분석 60
4.3. TiVZrNb계 경량 고엔트로피 합금 기계적 물성 70
4.3.1. TiVZrNb계 합금 경도 70
4.3.2. TiVZrNb계 합금 압축 및 인장 73
4.4 미세조직과 기계적 물성의 상관관계 82
제5장 결론 93
1) TiVZrNb 계 고엔트로피 합금의 미세조직 및 기계적 특성 93
1) TiVZrNb 계 고엔트로피 합금의 미세조직 및 기계적 특성의 상관관계 95
참고문헌 97
Table 4.1. designed TiVZrNb alloy composition. 58
Table 4.2. density and atomic radius of compositional elements. 59
Table 4.3. Chemical composition (in at%) of the TiVZrNb alloy samples examined by EDS analysis. 64
Table 4.4. Results of density measurement using Archimedes method. 69
Table 4.5. Compression mechanical properties in terms of yield strength (σy), compression strength (σm) and total elongation (ε)...[이미지참조] 76
Table 4.6. Tensile mechanical properties in terms of yield strength (σy) and total...[이미지참조] 78
Table 4.7. FWHM of the 1st peak of the Pair distribution function[이미지참조] 87
Table 4.8. The values △б0.2, (б0.2)mix, △бG, △бa of each alloy.[이미지참조] 90
Fig. 1.1. (a)~(d) Back-scattered electron micrographs and (e) compressive stress-strain curves of AlLiMgZnSn alloys. 18
Fig. 2.1. Composition design range of conventional alloys and high-entropy alloys. (a) High-entropy alloys, (b) Commercial alloys. 22
Fig. 2.2. Change of the mechanical properties dependent on precipitation. 23
Fig. 2.3. 4 core effect of High-entropy alloys. 26
Fig. 2.4. High entropy alloys with severe lattice compared to pure metal. 27
Fig. 2.5. Diffusion factors and temperature graphs of Cr, Mn, Fe, Co, and Ni. 28
Fig. 2.6. Comparison of High Temperature Properties of commercial alloys and bcc-based High Entropy Alloys. 30
Fig. 2.7. Engineering stress vs. engineering strain compression curves of the TaNbHfZrTi alloy at different temperatures. 31
Fig. 2.8. Engineering stress vs engineering strain compression curves for TaNbHfZrTi alloys and... 32
Fig. 2.9. Schematic illustration of solid-solution hardening model in multi-component alloys. 34
Fig. 2.10. Schematic representation of the variation of yield stress as a function of grain size. 36
Fig. 2.11. Precipitation hardening diagram as a function of particle radius. 38
Fig. 3.1. Schematic illustration of Arc-melting equipment and alloying geometry. 40
Fig. 3.2. As-cast microstructure of Ti40V30Zr20Nb10 with segregation.[이미지참조] 42
Fig. 3.3. Schematic illustration of Heat-treatment method and Cold-rolling equipment. 44
Fig. 3.4. Measured density by Archimedes principle. 47
Fig. 3.5. (a) indentation hardness (b) Measured hardness more than 10 times. 49
Fig. 3.6. Geometry of tensile and compression test samples. 51
Fig. 3.7. the meaning of peak width in PDF graph 55
Fig. 4.1. EDS element map of Ti50V30Nb10Zr10 (a) as-cast and (b) after thermal treatment at 1100℃ for 1 hour.[이미지참조] 63
Fig. 4.2. EBSD orientation maps of (a) Ti40V30Zr20Nb10 (b) Ti40V40Zr10Nb10 (c) Ti50V30Zr10Nb10 (d) Ti50V40Zr5Nb5 alloys at as-cast state.[이미지참조] 65
Fig. 4.3. As-homogenized microstructure of (a) Ti40V30Zr20Nb10 (b) Ti40V40Zr10Nb10 (c) Ti50V30Zr10Nb10 (d) Ti50V40Zr5Nb5.[이미지참조] 66
Fig. 4.4. X-ray diffraction patterns of (a) as-cast (b) after thermal treatment for 1hour at 1100℃ (c) EBSD phase analysis of as-cast. 67
Fig. 4.5. Change of peak of Ti40V30Zr20Nb10 before and after heat treatment.[이미지참조] 68
Fig. 4.6. Micro vickers hardness (a) as-cast (b) after thermal treatment for 1hour at 1100℃. 72
Fig. 4.7. compression stress-strain curve of the thermomechanically treated TiVZrNb alloys. 75
Fig. 4.8. Overall tensile stress-strain curve of the thermomechanically treated TiVZrNb alloys. 77
Fig. 4.9. The specific yield strengths of TiVZrNb alloys. 79
Fig. 4.10. Fracture surface after tensile test (a) Ti40V30Zr20Nb10 (b) Ti40V40Zr10Nb10 (c) Ti50V30Zr10Nb10 (d) Ti50V40Zr5Nb5[이미지참조] 80
Fig. 4.11. Microstructure of etched (a) Ti40V30Zr20Nb10 (b) Ti50V40Zr5Nb5[이미지참조] 81
Fig. 4.12. (a) Pair Distribution Function (PDF) and (b) FWHM of 1st shells.[이미지참조] 86
Fig. 4.13. Local lattice strain(ε) and Atomic size misfit(δ). 88
Fig. 4.14. (a) Atomic size misfit(δ) vs Hardness (b) Atomic size misfit(δ) vs Compression stress. 89
Fig. 4.15. a change in local lattice strain(ε) and lattice-mismatch strengthening(△σa) depending on the change in atomic size misfit(δ).[이미지참조] 91
Fig. 4.16. Atomic size misfit(δ) vs Specific yield strength. 92