Microstructure And Properties Of SiCp/SiC(CVI) Composite

SiC is of low density, high hardness, low dilatability, high thermal conductivity, high thermal-strength, good resistance to oxidation and thermal-shock. However the inadequate toughness limits its application. Fiber, whisker, and particle are used to solve this problem usually at present. Fracture of fiber composites are similar with metals, they have thick skin to crack and super reliability to be unable to occur tragedy. Particle composite is of isotropy and low cost, it is supplement to fiber composites. The traditional sintered ceramic matrix composite is insufficient of toughness, microstructure is not designed, and can not be applied to make big and thin components. However, the composites by Chemical Vapor Infiltration(CVI) can make up the shortage.In this thesis, SEM, XRD, EDS and TEM are applied to research the relationship of microstructures and properties, destroy mechanism of SiCp/SiC composite by CVI. The following are the main research content and conclusions:1 Microstructure of preform by granulation and forming were researched. Two kinds of holes are found in the preform: holes about several micrometers among the particles and holes about several millimeters among the conglomerations, which are similar with fiber preform. The shape of conglomeration is irregular after forming, so the hole are different from those in the fiber bundles.2 Structure of interphase and mechanism of SiCp/SiC composite were researched. The result indicate: the interphase was glass state carbon, the thickness is about 0.1μm, and the glass state carbon is not combined with particle tightly, there are about 0.15μm SiC matrix between them, carbon interphase incurred weak joint. The microstructure lead to low strength of the composite and brittleness fracture.3 Microstructures of by removing carbon were researched. The results indicate: a bit carbon was removed, and weak interphase joint exist still and did not build up the boundary strength.4 Oxidation properties of SiCp/SiC composite were researched. The result indicate:the bending strength of SiCp/SiC reduced about 20% after oxidization.