.c / Sic Composite Material Structure And Mechanical Properties

C/SiC show superior oxidation resistance in comparison to Carbon/Carbon(C/C), and be considered as the most promising thermal structural candidate materials which can be used at high thrust-weight ratio aero-engine, liquid rocket motor(LRM), solid rocket motor(SRD), scamjet motor as well as thermal protection system(TPS) on re-usable shuttles, advanced friction and clutch systems of brake industry. In this research work, carbon fiber reinforced silicon carbide(C/SiC) composites were made of 2.5D carbon fiber integer felt and 3D performs by chemical vapor infiltration-reactive melt infiltration(CVI-RMI) and chemical vapor infiltration(CVI) method, respectively. Microstructure and compositions of 2.5D,3D CVI-C/SiC and CVI-RMI-C/SiC composites were observed. The flexural,tensile properties, fracture toughness and fracture mechanism of composites were thoroughly investigated. The main contents and conclusions of this work are as follows:(1) When SiC matrix were deposited by CVI, the results showed that pureβ-SIC can was deposited at all temperature from 1100℃to 1400℃,β-SiC owned a preferred orientation of(111) plane, and the crystal size ofβ-SiC increased consistently with temperature below 1300℃. When SiC matrixes were prepared by RMI, Si and SiC compositions were coexisted. The crystal size ofβ-SiC of (111) plane by RMI method was 62.5 nm on 1100℃, larger than CVI-SiC matrix.(2) To 2.5D CVI-C/SiC composites PyC interface coating and CVI-SiC matrix were deposited uniformly on C fibers. Density of composites was 2.1g.cm^-3. but little of hole were leaved with 10% open hole. CVI-RMI method taked little time, and could fill enough in the hole in the C fiber preforms, with high density of 2.25 g.cm(-3) and open hole of 10.2%. 3D CVI-RMI-C/SiC composites owned higher density then 3D CVI-C/SiC composites, with many advantage that low cost, short process and low open hole, and with a disadvantage that existed no reaction between little carbon and Si.(3) To 2.5D CVI-C/SiC composites, the flexural strength of C/SiC composites increased with the increase of density, and the maximal flexural strength of C/SiC composites was 329MPa. When the density of composites was 1.95 g.cm^-3, the fracture toughness was the larger than others and the value was 13.6 MPa·m^1/2. When composites have low density, C fibers were pulled out much, because of the weak interface combinability between SiC matrix and fiber, and showed toughness fracture behavior. When high density, composites showed brittleness fracture behavior. To 3D CVI-C/SiC composites, the flexural strength of composites increased, and fracture behaviors of composites transited from tough fracture to brittle fracture, with the increase of density. When the density of composites was 2.11 g.cm^-3, the maximal flexural strength of C/SiC composites was 465MPa. Tensile strength of 3D CVI-C/SiC composites was up to 168MPa, but tensile strength of 2.5D CVI-C/SiC composites was only 103MPa.(4) To 2.5D CVI-RMI-C/SiC composites, the density of C/SiC composites increased, but flexural strength decreased, and fracture behaviors of composites transited from tough fracture to brittle fracture, with the increase of RMI infiltration temperature. The maximal flexural strength of C/SiC composites was 131MPa. As the CVI-SiC matrix content increasing, flexure strength of C/SiC composites increased, and fracture behaviors of composites transited from tough fracture to brittle fracture. Tensile strength of 2.5D CVI-RMI-C/SiC composites was only 15 MPa, and showed hybrid fracture character. To 3D CVI-RMI-C/SiC composites, the density of composites which density was 1.5 g.cm^-3 after CVI, was larger than the composites which density was 1.3 g.cm^-3 after CVI, and flexural strength was 364 MPa.