Papers by Keyword: SiC_f/SiC Composites

Abstract: Microstructure and mechanical/thermal properties of SiCf/SiC composites additionally reinforced with SiC nanowires were investigated. SiC nanowires could be grown successfully within the SiC fiber preform by a chemical vapor infiltration (CVI) process through a control of the deposition parameters. The incorporation of the SiC nanowires into the fiber perform was clearly shown to be effective in increasing the efficiency of the matrix infiltration, and thus resulted in a higher density in a shorter CVI time. The modification of the pore structure and the reduction of the macro-pores in the composite resulted in higher mechanical and thermal properties than the conventional CVI counterpart. The matrix deposition on both surfaces of the SiC fibers and nanowires induced smaller matrix grains in the nanowire-reinforced composite, and thus a higher hardness and elastic modulus than the conventional one after an ion irradiation.

Abstract: To estimate the ion-irradiation effect on various types of SiCf/SiC composites, a silicon self-ion irradiation was performed at temperatures of 600 °C and 1200 °C and at doses of 5 dpa and 20 dpa, respectively. These SiCf/SiC composites were prepared by different processes such as CVI (chemical vapor infiltration), WA-CVI (SiC whisker assisted CVI) and hot-pressing (HP) method. Hardness was measured by a nano-indentation tester and microstructural changes were observed by TEM with SAD(selected area diffraction) technique for the specimens prepared by FIB (Focused Ion Beam) milling. The damage dose was calculated by the SRIM2003 code and then compared with microstructureal observation.

Abstract: Several 2D SiCf-SiC and Cf-SiC composites were fabricated using isothermal and isobaric Chemical Vapour Infiltration (ICVI) process. The reinforcements used in the above composites are Nicalon CG fabric and C fabric. Prior to SiC matrix infiltration, BN and C interfaces were applied to the fibre by using the pre-cursors Boron Trichloride (BCl3)-Ammonia (NH3) and Methane (CH4) respectively to improve the mechanical performance of the composites. SiC matrix was infiltrated by the decomposition of Methyl Trichloro Silane-CH3SiCl3 (MTS) in the presence of hydrogen at the temperature ranging from 950°C to 980°C. H2/MTS flow rate ratio used for this study is 16:1.An appropriate temperature for uniform SiC infiltration without any premature pore closures have been obtained by kinetic experiment. Density and porosity of the above composites were measured using the method described by EN1389:2003. Various mechanical characterizations like flexural strength, tensile strength and fracture toughness of the SiCf-SiC composites were also studied. The SiCf-SiC composites were subjected to thermal exposure (1000°C for 100 hr in an oxidizing atmosphere) and tensile strength results obtained before and after thermal exposure were compared. RT Flexural Strength and Fracture Toughness (KIC) of composite-SQAV (SiCf/C/SiC) and composite-SQBII ( SiCf/BN/SiC ) are measured by 3-point bending and results were compared. RT Flexural strength of Cf-SiC composites with C interface of two thicknesses were measured and

Abstract: SiC nanowires could be grown homogeneously within SiC fiber preforms by controlling the concentration of a reactant gas. The morphology and the growth behavior of the SiC nanowires were largely dependent on the degree of the reactant supersaturation. The SiC nanowires incorporated in the fiber preform increased the surface area at which the matrix deposition could take place, enhancing an efficiency of the matrix infiltration and altering the remaining pore structure of the SiCf/SiC composite.

Abstract: In the polymer impregnation and pyrolysis (PIP) process for the fabrication of SiCf/SiC composite, the curing process should be included to increase the conversion yields. During the curing process, unintended oxygen is introduced. Control of this oxygen is very important to obtain composites with a good high temperature stability. Using the electron beam curing process with full doses of 2~10 MGy and the pyrolysis process at 1300~1500oC, composites with an oxygen contents of less than 1 wt% could be obtained.

Abstract: Continuous SiC fiber reinforced SiC composites were fabricated by PIP route and their microstructures and mechanical properties were characterized. The density, flexural strength and fracture toughness of the composites were 1.88 g/cm3, 307 MPa and 8.24 MPa⋅m1/2, respectively. The low mechanical properties were ascribed to low density and strong interfacial bonding. The composites exhibited poor oxidation and thermal shock resistance; however, they showed desirable thermal stability.

Abstract: This study presents the results of mechanical tests of commercial 2D SiCf/SiC ceramic matrix composite for fusion reactors applications. The creep behaviour was investigated by means of flexural constant load stress-rupture tests, in controlled atmosphere at 600 and 1000°C. The creep strain and time to failure vary with applied load according to a power law. Cyclical tests at room temperature and at high temperature showed that the material has a good fatigue behaviour at room temperature, as no evident fatigue damage was detected after 80.000 cycles at a peak load up to 98 % of MOR. Conversely at high temperature (1000°C) the specimens showed a progressive compliance increase and limited cycles to failure even at peak load as low as 40 % of MOR. Creep phenomena seem to influence the fatigue behaviour. Creep strain analysis, crack growth and fracture surface observations allowed to investigate the mechanisms that affect the crack propagation, the fracture process and the rupture life under cyclic loading and under constant stress loading at different temperatures.

Abstract: To obtain a dense SiCf/SiC composite by the chemical vapor infiltration (CVI) process, whisker growing before matrix filling was applied, which is called the whisker growing assisted CVI process. The whisker growing and matrix filling processes were carried out using MTS (CH3SiCl3) and H2 as source and diluent gases, respectively. Tyranno-SATM was used as a reinforced substrate. Characterizations of SiC whisker grown during the in situ whisker growing process have been investigated. The weight gain rates with the matrix filling time and the density of composites was measured. The flexural strength with the thickness of the pyrolytic carbon (PyC) interlayers has been evaluated. b-SiC whiskers with many stacking faults were grown well in the Tyranno SATM fabrics. Tyranno-SA/SiC composite with a PyC interlayer thickness of 150 nm had a flexural strength of 610 MPa and the density of 2.71 g/cm3.

Abstract: SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. SiCf/SiC composites are promising for various structural materials. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of the process temperature and pressure is key requirements for the fabrication of SiCf/SiC composites by hot pressing method. In the present work, monolithic LPS-SiC was fabricated by hot pressing method at various temperatures. The starting powder was high purity β-SiC nano-powder with an average particle size of 30nm. Compositions of sintering additives were Al2O3 / Y2O3 = 0.7 and 1.5 (wt.%). Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the process temperature. Particularly, relative density of LPS-SiC fabricated at 1820oC with additive composition of Al2O3/Y2O3=1.5(wt.%) was 95%. Also, flexural strength and elastic modulus were 900MPa and 220GPa, respectively. In the fracture surface of this specimen, the size and shape of SiC grains grew up and changed. Also, tortuous crack paths and occurrence of interfacial debonding were observed.

Abstract: The characterization of RS-SiC and RS-SiCf/SiC composite materials fabricated by the reaction sintering process has been investigated, based on the detailed examination of their microstructures. In this composite system, Tyranno SA SiC fiber and Hi-Nicalon SiC fiber were used as reinforcing materials. The green bodies for RS-SiC and RS-SiCf/SiC materials were prepared with the complex matrix slurry of SiC and C particles. The density and the room temperature strength of RS-SiC material with the starting SiC particles of 0.3 µm showed about 3.1 Mg/m3 and about 520 MPa, respectively, even if there were large amount of residual silicon (about 19 %). The flexural strength of Hi-Nicalon/SiC composites greatly decreased at the temperature higher than 1000 􀀀