Title Page
ABSTRACT
국문 초록
Contents
NOMENCLATURE 15
CHAPTER 1. INTRODUCTION 17
CHAPTER 2. Theoretical background 23
2.1. Interfacial properties between fiber and matrix 23
2.2. SiC matrix densification process 32
CHAPTER 3. Experimental 34
3.1. Interphase coating 34
3.1.1. PyC interphase 34
3.1.2. BN/PyC interphase 39
3.2. SiC matrix densification 40
3.2.1. Computational fluid dynamics (CFD) 40
3.2.2. SiC deposition by CVI process 42
3.2.3. CVI/LSI/PIP hybrid infiltration process 45
3.3. Mechanical testing of SiCf/SiC composites[이미지참조] 46
3.3.1. High temperature tensile strength testing 46
3.3.2. Fracture toughness testing 46
3.3.3. High temperature fatigue testing 46
CHAPTER 4. Microstructure of PyC and BN/PyC interphase 47
4.1. PyC interphase 47
4.2. BN/PyC interphase 58
CHAPTER 5. Microstructure and mechanical properties of SiCf/SiC composites fabricated by CVI/LSI/PIP[이미지참조] 62
5.1. Optimization of CVI process 62
5.1.1. Analysis of fluid velocity distribution in preform 62
5.1.2. Density change of SiC composite with the holder shape 65
5.1.3. Microstructure of SiCf/SiC composites manufactured by hybrid process[이미지참조] 67
5.2. Mechanical properties of SiCf/SiC composites[이미지참조] 72
5.2.1. High temperature tensile strength 72
5.2.2. Fracture toughness 76
5.2.3. High temperature fatigue cyclic fatigue 79
CHAPTER 6. Conclusion 83
REFERENCES 85
Appendix 90
Table 1. Physical properties of 3rd generation Hi-Nicalon S fiber and Tyranno SA3 fiber 29
Table 2. CVI process conditions. 44
Table 3. Raman spectra of (a) P5 and (b) P100 51
Table 4. Comparison of mechanical properties of SiCf/SiC composites.[이미지참조] 75
Figure 1.1. Operating temperature of gas turbine engine materials as a function period of their dominant usage 21
Figure 1.2. Crack deflection, debonding, and fiber pull-out at fracture surface. 22
Figure 2.1. (a) Typical stress-strain curves and (b) pull-out fibers observed at the fracture surface of SiCf/SiC composites.[이미지참조] 27
Figure 2.2. (a) Interfacial shear stress and (b) proportional limit stress curve with the thickness of interphase 28
Figure 2.3. Interfacial shear strength of SiCf/SiC composites relative to SiC fiber roughness and crystallization of interphase.[이미지참조] 30
Figure 2.4. UTS and strain of SiCf/SiC composite according to ID/IG ratio extracted from Raman spectroscopy.[이미지참조] 31
Figure 3.1. (a) A normalized image (b) the binarized image where white represents the detected lattice fringe and black represents the background. (c) a skeletonized image (d)... 36
Figure 3.2. Quantitative analysis process of diffraction pattern of PyC interphase (a) center calibration, (b) diffraction pattern, (c) azimuthal projection, (d) (002) plane profile. 37
Figure 3.3. Classification of turbostratics with preferred orientation. 38
Figure 3.4. Reference preform holder (No.1) and newly designed graphite holder (No.2 ~ No.4). The area of the exhaust hole of the holder is the same. 41
Figure 3.5. Cross-sectional schematic of the CVI equipment. 43
Figure 4.1. Microstructure of (a) P5 and (b) P100 on fiber 49
Figure 4.2. X-ray diffraction pattern of (a) P5 and (b) P100 mixed with pulverized powders and silicon 50
Figure 4.3. Raman spectra of (a) P5 and (b) P100. 52
Figure 4.4. HRTEM image of (a) P5 (b) P100 53
Figure 4.5. Interlayer spacing between (a) P5 and (b)P100 extracted from digital image processing. 54
Figure 4.6. FFT diffraction pattern of (a) P5 and (b) P100. κ and φ denote the radial distance and azimuthal angle 55
Figure 4.7. Radial intensity profiles and the corresponding inter-planar spacings of (a) P5 and (b) P100. 56
Figure 4.8. Azimuthal projections of (a) P5 and (b) P100 and azimuthal profiles of the identified diffraction maxima for (c) P5 and (d) P100. 57
Figure 4.9. Cross-section and (b) surface morphology of BN-coated fibers (c) EDS profile of BN coated fiber. 59
Figure 4.10. FTIR spectrum of BN-coated SiC fiber. 60
Figure 4.11. HRTEM of (a) PyC interphase and (B) BN/PyC interphase. 61
Figure 5.1. The fluid velocity distribution inside the preform held by the reference holder (No.1) and the newly designed holder (No.2~No.4). 63
Figure 5.2. The fluid velocity distribution within the (a) R1 and (b) R2 preforms, (c) Comparison of fluid velocity within the preform. 64
Figure 5.3. Density increase rate at each step during the CVI process. 66
Figure 5.4. (a) Overall cross-sectional micrographs of SiCf/SiC composites fabricated by a hybrid process (b) micro-pores in fiber bundles.[이미지참조] 69
Figure 5.5. SEM micrographs of SiCf/SiC composites in local magnification CVI-SiC matrix around SiC fiber, (b) LSI-processed matrix near SiC bundle and (c) PIP-filled SiC...[이미지참조] 70
Figure 5.6. X-ray diffraction of SiCf/SiC composite fabricated by a hybrid process.[이미지참조] 71
Figure 5.7. Stress-strain curve of the SiCf/SiC composite fabricated by a hybrid process at 1400 ℃ in air.[이미지참조] 73
Figure 5.8. Fracture surface of SiCf/SiC composites fabricated by a hybrid process.[이미지참조] 74
Figure 5.9. Load-displacement curve of SiCf/SiC composite with PyC interphase and BN/PyC interphase.[이미지참조] 77
Figure 5.10. (a) Fracture toughness and Fracture surface of SiCf/SiC composite with (b) PyC interphase and (c) BN/PyC interphase.[이미지참조] 78
Figure 5.11. Fatigue test results at 1400 ℃ for SiCf/SiC composite with (a) PyC interphase and (b) BN/PyC interphase.[이미지참조] 80
Figure 5.12. The overall fracture surface of SiCf/SiC composite with (a) PyC and (b) BN/PyC interphase.[이미지참조] 81
Figure 5.13. Fracture surface of fiber coated with (a),(b) PyC and (c),(d) BN/PyC interphase after fatigue test 82