Research On Preparation And Properties Of Three-dimensional Carbon Fiber Reinforced Silicon Carbide Matrix Composites

Rapid fabrication techniques deciding composite microstructure and performance are one of the key directions for the development and application of carbon fiber reinforced silicon carbide matrix (C/SiC) composites. A systematic study on rapid fabrication of C/SiC composites have been made via experiments and theoretical analysis, combined with deposition and impregnation mechanism, mechanical properties, microstructure characterization in this dissertation.A Mass Transfer function based method has been proposed to describe the combined process of chemical-vapor-infiltration and polymer-precursor-infiltration-pyrolysis (the CVI-PIP process) for fabrication of the C/SiC composites. A series of important information related to the CVI-PIP densification have been achieved as following: the fiber coating thickness, porosity variety, packing rate of void, growth rate of closed void, evolution of bulk density, densification behavior, as well as the uniformity of coating and densification, etc. A series of design optimization for fabrication of C/SiC composites has been established via the CVI-PIP modeling program operation. The check experiment is finished to verify the accuracy of the model function, and the deviations between experiment and computational results are minor, which indicates that the model function have satisfied accuracy. An optimized CVI-PIP process has been achieved, by which the C/SiC composites with 2.1 Ig/cm3 high density and uniformity are fabricated in 200 hours.The microstructure and composition of pyrolytic carbon interphase and CVI-PIP silicon carbide matrix in the C/SiC composites are investigated with the help of Polarization Microscope, Scanning Electron Microscope, and X-ray Diffraction Technique, etc. The structure characteristic of pyrolytic carbon interphase and CVI-PIP silicon carbide matrix, and effects of CVI-PIP process on it are summarized and discussed. By growth course and feature of pyrolytic carbon interphase and CVI-PIP silicon carbide matrix analyzed, a whole-course densification mechanism of lamellar -growth-pattern is proposed to explain the densification phenomenon, which makes asystematic understanding on the feature of pyrolytic carbon interphase and CVI-PIP silicon carbide matrix, and the multiple stitching interface binding. Further, the mechanical behavior and fracture features under flexural load of the C/SiC composites are discussed with mechanical properties contract to microstructure and CVI-PIP process parameters. The multiple fracture phenomenon of the C/SiC with high toughness connected to multiple interface fracture is found, which supplements the conventional composite theory on the relationship between strength and fracture mode.Systematic characterization results demonstrates that the mechanical properties, thermal performance,and thermal shock resistance of the C/SiC composites fabricated by the CVI-PIP process are exceed the desired level of the research: the flexural strength up to 743MPa, fracture toughness up to 17.9 MPa.m , shear strength up to 55.5 MPa. The results of static firing test shows that the thermal erosion properties, mechanical properties, tand thermal shock resistance of the C/SiC composites can meet a demand for thermal-structure application in the area of Aerospace such as liquid rocket thruster .