표제지
국문요약
영문요약
목차
제1장 서론 22
1.1. 연구 배경 23
1.2. 연구 목적 26
1.3. 참고문헌 27
제2장 이론적 배경 34
2.1. 적층 제조 35
2.1.1. Laser powder bed fusion (LPBF) 36
2.1.2. Direct metal deposition (DED) 38
2.2. 오스테나이트계 경량 철강 40
2.3. Inconel 718 격자 구조체 42
2.4. 참고문헌 45
제3장 LPBF 공정으로 제조된 오스테나이트계 경량 철강의 미세조직 및 인장, 충격 및 고주기 피로 특성 51
3.1. 서론 52
3.2. 실험 방법 54
3.2.1. 소재 54
3.2.2. 미세조직 분석 56
3.2.3. 인장 시험 57
3.3. 결과 58
3.3.1. 미세조직 58
3.3.2. Nano sized B2 precipitate 60
3.3.3. 인장 특성 60
3.3.4. 인장 파단면 61
3.3.5. 고주기 피로 특성 61
3.4. 고찰 63
3.5. 결론 65
3.6. 참고문헌 83
제4장 후열처리를 통한 LPBF 공정으로 제조된 오스테나이트계 경량 철강의 미세조직 제어, 인장 및 고주기 피로 특성 평가 91
4.1. 서론 92
4.2. 실험 방법 94
4.2.1. 소재 94
4.2.2. 후열처리 94
4.2.3. 미세조직 분석 94
4.2.4. 인장 시험 96
4.3. 결과 97
4.3.1. 미세조직 차이 97
4.3.2. 상온 인장 특성 99
4.3.3. 고주기 피로 특성 100
4.4. 결론 101
4.5. 참고문헌 116
제5장 Laser Powder Bed Fusion 공정으로 제조된 IN718 격자구조체의 미세조직 및 상온 압축 특성에 미치는 형상 및 크기의 영향 125
5.1. 서론 126
5.2. 실험 방법 127
5.3. 결과 및 고찰 129
5.3.1. 구조적 & 미세조직적 특징 129
5.3.2. 상온 기계적 특성 130
5.4. 고찰 131
5.4.1. 기계적 특성에 미치는 격자 형상 및 크기의 영향 131
5.5. 결론 134
5.6. 참고 문헌 150
제6장 Laser Powder Bed Fusion 공정으로 제조된 IN718 격자 구조체의 미세 조직 및 압축 특성에 미치는 후열처리의 영향 155
6.1. 서론 156
6.2. 실험 방법 157
6.3. 결과 160
6.3.1. 표준 시효 처리가 미세조직에 미치는 영향 160
6.3.2. 상온 및 650℃ 기계적 특성 161
6.4. 고찰 162
6.4.1. 압축 변형 거동에 미치는 격자 형상 및 미세조직의 영향 162
6.5. 결론 165
6.6. 참고 문헌 180
제7장 결론 185
7.1. 결론 186
7.1.1. Laser Powder Bed Fusion 공정으로 제조된 오스테나이트계 경량 철강의 미세조직 및 인장 및 고주기 피로 특성 186
7.1.2. 후열처리를 통한 LPBF 공정으로 제조된 오스테나이트계 경량 철강의 미세조직 제어, 인장 및 고주기 피로 특성 평가 187
7.1.3. Laser Powder Bed Fusion 공정으로 제조된 IN718 격자구조체의 미세조직 및 상온 압축 특성에 미치는 격자 형상 및 격자 크기의 영향 188
7.1.4. 후열처리된 LPBF 제조 IN718 격자 구조체의 미세조직 및 650도 고온 압축 특성에 미치는 격자 형상의 영향 189
Achievements 190
Papers 191
Conferences 193
Awards 195
Table 2-1. Typical characteristics of each metal AM process. 39
Table 3-1. Chemical compositions of carbon-bearing ultra-high strength high Co-Ni steel in the powder and LPBF-built samples utilized in this... 66
Table 3-2. Processing parameter values of LPBF process for Fe-16Mn-10Al-5Ni-0.86C lightweight steel. 70
Table 5-1. Dimensions and physical properties of Inconel 718 microlattciestructures manufactured by LPBF. 137
Table 5-2. LPBF Processing parameter of IN718 lattice structure. 140
Table 5-3. Compressive properties of Inconel 718 lattice structures. 145
Table 6-1. Dimensions of strut based lattice structure. 168
Table 6-2. Maxwell number, M for Inconel 718 micro-lattice examined in this study. 177
Figure 2-1. Representative microstructure of a LPBF-built austenitic 316L stainless steel. 35
Figure 2-2. Laser powder bed fusion for ultra-high strength steel. 37
Figure 2-3. Schematic diagram of powder bed of L-PBF process. 37
Figure 2-4. Direct energy deposition for high carbon tool steel. 38
Figure 2-5. (a) density reduction ratio by adding Al element, and (b) B2-IMC strengthening mechanism. 40
Figure 2-6. Nano sized B2-IMC which resist dislocation movement (a-b) and κ-carbide sheared by dislocation (c). 41
Figure 2-7. Effect of Al content on density 41
Figure 2-8. Strut-based lattice topologies: (A) BCC; (B) BCCZ; (C) FCC; (D) FCCZ; (E) cubic; (F) octettruss; (G) diamond. 43
Figure 3-1. Pre-alloyed powder characteristics; (a) powder morphologies, and (b) particle size distribution. 67
Figure 3-2. OM images showing the flaws in LPBF samples with different scan speed. 68
Figure 3-3. (a) Diagram of LPBF build strategy and (b) macro image of bar-type Fe-16Mn-10Al-5Ni-0.86C lightweight steel. 69
Figure 3-4. XRD analysis results showing (a) constituent phases of LPBF-built [black line]and Conventional LWS specimen [red line] of... 71
Figure 3-5. EBSD phase mapsshowing constituent phases of LPBF-built and Conventional LWS specimen of Fe-16Mn-10Al-5Ni-0.86C LWSby direction. 72
Figure 3-6. EBSD Inverse pole figure, Kernel average misorientation map and phase mapof LPBF-built and Conventional LWS specimen of Fe-16Mn-10Al-5Ni-0.86C LWS. 73
Figure 3-7. The phase fraction and its size distribution of both lightweight steel by EBSD phase map. 74
Figure 3-8. High-magnification band contrast map (a) and phase map (b) showing Kurdjumov-Sachs orientation relationship [red line]between nano-sized B2-IMC and austenite matrix. 75
Figure 3-9. HAADF-STEM, (a2) SADP, (b1) STEM, and (b2) EDS line profile of STEM images showing the B2-ordered intermetallic... 76
Figure 3-10. Unaxialtensile properties of both LWSs; (a) engineering stress-strain curve and (b) comparison to other conventional LWSs, and... 77
Figure 3-11. SEM micrographs of the tensile fractured surface of both lightweight steels. 78
Figure 3-12. High magnification HR-EBSD analysis results of tensile deformed specimen: (a) LPBF LWS and (b) Conventional LWS. 79
Figure 3-13. Yield strengths calculated by applying various strengthening mechanisms such as solid solution hardening, precipitate... 80
Figure 3-14. S-N curves of LPBF and conventional LWS. 81
Figure 3-15. Fatigue fractographies showing the different failure behavior between with- and without-defects; (a1-3) with defect and... 82
Figure 4-1. ThermoCalc result showing the fraction of phases of Fe-16Mn-10Al-5Ni-0.86C lightweight steel by temperature. 102
Figure 4-2. Schematic diagram of post heat treatment for LPBF LWS: (a) annealing and (b) tempering. 103
Figure 4-3. X-ray diffraction patterns of LPBF LWSs after post heat-treatment. 104
Figure 4-4. EBSD inverse pole figure map and kernel average misorientation map of post heat treated LPBF LWS. 105
Figure 4-5. EBSD phase map showing austenite matrix and B2-IMC of post heat treated LPBF LWS by plane. 106
Figure 4-6. Fraction and size distribution of constitutient phases of LPBF LWS by different post heat treatment. 107
Figure 4-7. High-magnification band contrast map and phase map showing Kurdjumov-Sachs orientation relationshipbetweennano-sized B2-IMC and austenite matrix. 108
Figure 4-8. Backscattered image (a) LPBF LWS, (b) A30, and (c) DT showing constituent phases. 109
Figure 4-9. Electronprobemicro analysis showing distribution of alloy element by post heat treatment. 110
Figure 4-10. (a) Tensile stress-strain curve of LPBF LWSs and (b) compareto other conventional LWSs. 111
Figure 4-11. Tensile fractured surface of LPBF LWS by different post heat-treatment. 112
Figure 4-12. EBSD phase map and KAM map showing higher misorientation along the phase boundary. 113
Figure 4-13. (a) S-N curve of LPBF LWSs and (b) plotting by maximum stress / yield stress ratio. 114
Figure 4-14. Fatigue fractured surface of LPBF LWSs and its high magnification on fatigue crack initiation region. 115
Figure 5-1. Unit cell structures examined in this study: (a) BCC; (b) BCCZ; (c)FCC; (d)FCCZ. 136
Figure 5-2. (a) Secondary electron micrograph of the Inconel 718 powder morphology; (b) Inconel 718 powder size distribution determined by laser... 138
Figure 5-3. Macroscopic view of twelve (12) additively manufactured Inconel 718 micro-lattice structures examined in this study. 139
Figure 5-4. Measured relative density (ρ/ρs) of Inconel 718 lattice structures. 141
Figure 5-5. Representative strut surface of as-built Inconel 718 micro-lattice structures. 142
Figure 5-6. The cross-sectional image of as-built BCCZ2lattice structure shows dendritic microstructure (a-c), and BCC 4 showing similar... 143
Figure 5-7. Engineering compressive stress-strain curves for as-built micro-lattice structures. Unit cell topology and size are distinguished in... 144
Figure 5-8. Graphic summary of 2mm unit cell micro-lattices including 2% strain, 10% strain, 20% strain and 30% strain. 146
Figure 5-9. Graphic summary of 3mm unit cell micro-lattices including 2% strain, 10% strain, 20% strain and 30% strain. 147
Figure 5-10. Graphic summary of 4mm unit cell micro-lattices including 2% strain, 10% strain, 20% strain and 30% strain. 148
Figure 5-11. Macro-image of 4mm unit cell IN718 lattice structures after compression test (ε=60%). 149
Figure 6-1. Representative strut surface of as-built Inconel 718 micro-lattice structures. 167
Figure 6-2. (a) Schematic diagram of post heat treatment for IN718 lattice structure and (b) TTT diagram of conventional IN718. 169
Figure 6-3. Relative density measurement of BCC, BCCZ, FCC, FCCZ lattice sturcutre. 170
Figure 6-4. The cross-sectional image of as-built lattice structure shows melt pool structure (a-c) and cellular, columnar microstructure (d-e). 171
Figure 6-5. The cross-sectional image of standard aged lattice structure shows equiaxed grain (a) and gamma second prime (d), (b-c) and (e-f)... 172
Figure 6-6. Compressive stress-strain curves at RT and 650℃ of as-built and standard aged IN718 lattice structure. 173
Figure 6-7. SEM image shows compressive deformed as-built and standard aged IN718 lattice structure at RT. 174
Figure 6-8. SEM image shows compressive deformed as-built and standard aged IN718 lattice structure at 650℃. 175
Figure 6-9. Column graph compared to the compressive yield strength by lattice structure at RT and 650℃. 176
Figure 6-10. Finite element analysis of compressive deformed at 0.04 % of IN718 lattice structure: BCC, BCCZ shows higher Von mises stress on... 178
Figure 6-11. Von Mises stress shows higher at node than strut, When equipped with a Z-strut, it is deemed that higher stress is concentrated... 179