표제지
ABSTRACT
국문 초록
목차
Ⅰ. 서론 13
1.1. 금속 적층제조 (Additive manufacturing) 13
1.2. Al-Si-Mg 합금 14
1.3. 잔류응력 15
1.4. 미세조직 분석 19
Ⅱ. 이론적 배경 20
2.1. 비파괴적 분석 방법 20
2.1.1. sin²Ψ 방법 20
2.1.2. cosα 방법 29
2.1.3. 중성자 회절법 38
2.2. 파괴 및 반파괴적 분석 방법 41
2.2.1. 파괴적 분석 방법 41
2.2.2. 나노인덴테이션 42
2.3. Electron channeling contrast imaging (ECCI) 50
Ⅲ. 실험 방법 54
3.1. 재료특성 평가 55
3.2. A356.2 분말의 LPBF 공정 및 후 열처리 59
3.3. 잔류응력 측정 63
3.4. 미세조직 분석 67
Ⅳ. 결과 및 고찰 68
4.1. 미세조직 분석 68
4.2. 잔류응력 분석 75
4.2.1. sin²Ψ 방법 75
4.2.2. cosα 방법 78
4.2.3. 나노인덴테이션 82
4.2.4. 중성자 회절법 95
Ⅴ. 결론 101
REFERENCES 103
Table 1. Chemical composition of the A356.2 powder used for additive manufacturing 57
Table 2. Flow properties of A356.2 powder: (a) Flow rate, (b) Apparent density and (c) Tap density 58
Table 3. Process variables for LPBF additive manufacturing 60
Table 4. Heat treatment conditions and additive manufactured samples 61
Table 5. Residual stress of samples obtained using the sin²Ψ method 77
Table 6. Residual stress of samples obtained using the cosα method 81
Table 7. Mechanical properties and stress of samples using the nanoindentation method;... 85
Table 8. Mechanical properties and stress of samples using the nanoindentation method;... 87
Table 9. Mechanical properties and stress of samples using the nanoindentation method;... 89
Table 10. Mechanical properties and stress of samples using the nanoindentation method;... 91
Table 11. Surface residual stress values among all measurement methods 94
Table 12. Residual stress measurement results using the neutron diffraction 98
Table 13. Residual stress measurement results using the neutron diffraction (Average value of LD, TD, ND) 100
Fig. 1. Schematic illustration of the as-built samples 17
Fig. 2. Schematic illustration of mechanism of residual stress formation in PBF 18
Fig. 3. Bragg's law (diffraction of X-ray in crystal) 21
Fig. 4. Residual stress measurement principle using X-ray diffraction 23
Fig. 5. Strain component in arbitrary direction for three-dimensional stress state in polar coordinates 24
Fig. 6. Example of dφΨ vs. sin²Ψ plot[이미지참조] 28
Fig. 7. Schematic illustration of the measurement principle based on cos α method 30
Fig. 8. Debye-ring recorded on a two-dimensional detector by a single exposure of X-rays 31
Fig. 9. Strain measurement of a Debye-ring in the cos α method 34
Fig. 10. cos α and sin α diagram 37
Fig. 11. Schematic illustration of the principle of neutron diffraction measurement 40
Fig. 12. Schematic illustration of indentation load-depth curve 43
Fig. 13. Schematic illustration of the loading and unloading process showing parameters characterizing the contact geometry 44
Fig. 14. Change of the load-depth curve upon nanoindentation with the residual stress 47
Fig. 15. Schematic illustration of the role of tensile and compressive residual stress at the indented surface 49
Fig. 16. Schematic illustration of mechanism of electron channeling contrast imaging 52
Fig. 17. Schematic illustration of backscattering electron intensity difference with dislocation 53
Fig. 18. (a) Scanning electron microscopy (SEM) image, (b) Particle size distribution, and (c) X-ray diffraction (XRD) pattern for the A356.2 powder 56
Fig. 19. Sample preparation for neutron diffraction residual stress measurement; (a) sample manufactured by LPBF process and (b) stress-free sample 62
Fig. 20. Schematic illustration of the incident beam direction to the sample; (a) φ=0° and (b) φ=90° 65
Fig. 21. Experimental setup for the neutron diffraction measurement 66
Fig. 22. Microstructures of additive manufactured A356.2 samples revealed by electron channeling contrast imaging (ECCI); magnification: x3,000 70
Fig. 23. Microstructures of additive manufactured A356.2 samples revealed by SEM-EDS analysis 71
Fig. 24. ECCI of the microstructure of as-built samples and stacking defects within Si precipitates in heat-treated samples;... 72
Fig. 25. Electron backscatter diffraction (EBSD) results (Top view): (a) image quality (IQ) maps, (b) grain boundary (GB) maps, (c) inverse pole figure (IPF) maps and (d) kernel average misorientation (KAM) maps 73
Fig. 26. Electron backscatter diffraction (EBSD) results (Side view): (a) image quality (IQ) maps, (b) grain boundary (GB) maps, (c) inverse pole figure (IPF) maps and (d) kernel average misorientation (KAM) maps 74
Fig. 27. sin²Ψ plots of the as-built and heat-treated samples in the (a) top view and (b) side view 76
Fig. 28. cosα mapping images of sample (Top view); (a)~(c) φ=0°, (d)~(f) φ=90° 79
Fig. 29. cosα mapping images of sample (Side view); (a)~(c) φ=0°, (d)~(f) φ=90° 80
Fig. 30. The load-depth curve of a nanoindentation test; Load: 10 mN 84
Fig. 31. The load-depth curve of a nanoindentation test; Load: 50 mN 86
Fig. 32. The load-depth curve of a nanoindentation test; Load: 100 mN 88
Fig. 33. The load-depth curve of a nanoindentation test; Load: 300 mN 90
Fig. 34. Mechanical properties and residual stress values under applied loads (10/50/100/300 mN); (a) Hardness, (b) Maximum depth and (c) Residual stress 92
Fig. 35. Comparison of surface residual stress values among all measurement methods 93
Fig. 36. Residual stress measurement results using the neutron diffraction 97
Fig. 37. Residual stress measurement results using the neutron diffraction (Average value of LD, TD, ND) 99