Fiber-reinforced SiC Matrix Composites Research Articles

EFFECT OF POROSITY ON PARTICLE EROSION WEAR BEHAVIOR OF LAB. SCALE SICF/SIC COMPOSITES

The use of silicon-based ceramics and composites as combustor liners and turbine vanes provides the potential of improving next-generation turbine engine performance, through lower emissions and higher cycle efficiency, relative to today's use of super alloy hot-section components. As a series of research for FOD resistant, a particle erosion wear test was carried out for continuous Pre- SiC fiber-reinforced SiC matrix composites with a new concept of lab. scale fabrication by LPS process. The result shows that aperture (some form of porosity) between fiber and interface has a deleterious effect on erosion resistance. Aperture along the fiber interfaces consequently causes a severe wear in the form of fiber detachment. Wear rate increase proportional as contents of open porosity increases. For nearly full dense composite materials of about 0.5 % porosity, are about 200 % more wear-resistant than about 5 % porous composites. Grain growth and consolidate condition of matrix which directly affects to FOD resistant are also discussed.

Tensile creep and rupture of 2D-woven SiC/SiC composites for high temperature applications

The tensile creep and rupture behavior of 2D-woven SiC fiber-reinforced SiC matrix composites with potential for advanced high temperature structural applications was determined in air at 1315 °C. The results are compared to similar SiC/SiC data in the literature in order to understand the underlying creep and rupture mechanisms. Focus was placed on three different near-stoichiometric SiC fiber-types and three SiC-based matrix systems produced by different process routes. In general, the creep and rupture properties of the tested composites were primarily dictated by the creep resistance of the fiber-type, with the Sylramic-iBN fiber typically showing the best behavior. However, the type of matrix did have an effect on the composite creep and rupture lives due to load-sharing differences for the different matrix types and due to stoichiometry in the case of chemical vapor infiltration SiC matrices.

Development of silicon carbide fiber-reinforced silicon carbide matrix composites with high performance based on interfacial and microstructure control

Continuous SiC fiber-reinforced SiC matrix composites (SiCf/SiC) have been considered to be a key material as structural components for aerospace and energy fields. This paper reviews novel fabrication process of continuous SiCf/SiC composites with high performance based on interfacial and microstructure control and our approach to improvement of mechanical and thermal properties of SiCf/SiC composite based on modeling and analysis. The simple fabrication process of two-dimensional SiCf/SiC composite using sheet stacking and hot-pressing based on interfacial and microstructure control was developed, and dense SiCf/SiC composite with excellent mechanical and thermal properties was successfully obtained. Furthermore, novel fabrication process of SiCf/SiC composite using EPD process was proposed and it was demonstrated that EPD process is expected to be an effective way to control the fiber/matrix interface and the microstructure of SiCf/SiC composite with high performance. Interfacial properties of SiCf/SiC composite were quantitatively evaluated by push-in test using nanoindenter, and these quantitative results well agreed with the results on their mechanical properties, and these results lead to the material design of the SiCf/SiC composite with high mechanical properties and the optimization of its fabrication process. Simple model of thermal conductivity of SiCf/SiC composite based on series model of multilayered structure was suggested by our experimental data, and higher thermal conductivity of SiCf/SiC composite was successfully achieved by microstructure control.

Dielectric properties of the SiC fiber-reinforced SiC matrix composites with the CVD SiC interphases

In this study, the SiC coating was deposited on the KD SiC fiber by CVD (chemical vapour deposition) process. The characteristics of the CVD SiC coating were evaluated by SEM, EDS and XRD analysis. Effects of the CVD SiC interphases on the porosity and dielectric properties of the SiC fiber-reinforced SiC matrix (SiCf/SiC) composites, fabricated by precursor infiltration and pyrolysis (PIP) process, were investigated. The results show that the permittivity of the SiCf/SiC composites with the CVD SiC interphases is very large at X-band, which is owing to the existence of the carbon-rich layers in the CVD SiC interphases. Finally, the microwave absorbing properties of the SiCf/SiC composites were simulated.

Effects of the fiber surface characteristics on the interfacial microstructure and mechanical properties of the KD SiC fiber reinforced SiC matrix composites

SiC fiber reinforced SiC matrix (SiC f/SiC) composites, employing two types of KD SiC fibers (from National University of Defense Technology, China) with different fiber surface characteristics as reinforcements, were fabricated by precursor infiltration and pyrolysis (PIP) process. The fiber surface characteristics were evaluated by SEM, XPS and Raman analysis. The effects of fiber surface characteristics on the interfacial microstructure and mechanical properties of the KD SiC f/SiC composites were investigated. The results show that the tensile strength of the KD-2 SiC fibers (with silicon-based oxide surface layers) is about 85% that of the KD-1 SiC fibers (with pyrocarbon (PyC) surface layers), but the flexural strength of the KD-2 SiC f/SiC composite is only around 15% that of the KD-1 SiC f/SiC composite. SEM, TEM and elemental mapping analysis show that the large strength difference between the two composites is ascribed to the interfacial microstructure and the degree of fiber damage, which are arising from the different fiber surface characteristics.

Microstructural investigations of the pyrocarbon interphase in SiC fiber-reinforced SiC matrix composites

The microstructure of the pyrocarbon interphase in SiC fiber-reinforced SiC matrix (SiCf/SiC) composites and its transformations during fiber/matrix debonding were studied. The phenomena of bridging and delamination within the pyrocarbon interphase are found during fiber/matrix debonding. A new phenomenon of ‘stress orientation’ of the basal planes of the pyrocarbon in the bridging region is discovered. It is found that the microstructural features of the pyrocarbon interphase are in favor of the toughness improvement of the SiCf/SiC composites.

Three-dimensional carbon fiber-reinforced silicon carbide matrix composites by vapor silicon infiltration

Three-dimensional carbon fiber-reinforced SiC matrix composites (C f/SiC) were fabricated by vapor silicon infiltration (VSI) successfully. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and wavelength dispersive spectrometer (WDS) analysis revealed that the microstructure and composition of constituent phases are strongly dependent on temperature. At 1973 K, the obtained C f/SiC composite mainly consists of SiC, carbon fiber and residual Si, and shows a densified microstructure. The flexural tests show non-catastrophic fracture behavior for composites fabricated by VSI process, and the ultimate flexural stress is comparable to those of composites fabricated by other processing techniques, demonstrating VSI is an effective way to fabricate the dense C f/SiC composites with good mechanical properties.

Monitoring damage accumulation in ceramic matrix composites using electrical resistivity

The electric resistance of woven SiC fiber-reinforced SiC matrix composites were measured under tensile loading conditions. The results show that the electrical resistance is closely related to damage and that real-time information about the damage state can be obtained through monitoring of the resistance. Such self-sensing capability provides the possibility of on-board/in situ damage detection and accurate life prediction for high-temperature ceramic matrix composites.

Stressed oxidation behaviors of SiC matrix composites in combustion environments

Performance of three kinds of continuous fiber reinforced SiC matrix composites prepared by chemical vapor infiltration (CVI) method, i.e. 2D C/SiC, 3D C/SiC and 3D SiC/SiC composites, have been investigated in the high temperature combustion environment gas with various creep stresses. The relationship between the life time of composite and the normalized peak strength, defined by the ratio of the test stress to the material strength, was studied. The life time of composites decreased with increasing the normalized peak strength following an exponential relationship. The oxidation resistance of the SiC/SiC composite was the best and that of the 2D C/SiC composite was the worst in the high temperature combustion environment with an applied stress. The experimental results suggested that there was a critical normalized peak strength which controls the oxidation mechanism of C/SiC. Below the critical normalized peak strength, the degradation of C/SiC in the combustion environment was controlled by the diffusion of oxygen and water vapor through the cracks in the composite. Above the critical normalized peak strength, the degradation was controlled by the oxidation of C fibers.

2748 BNコートHi-Nicalon繊維強化複合材料の熱サイクル疲労(S18-2 セラミックス(2),S18 セラミックスおよびセラミックス系複合材料)

BN coated Hi-Nicalon SiC fiber reinforced SiC matrix composites were evaluated under thermal cycling conditions. A surface of the specimen was heated by burner furnace and cooled by atmospheric air. The other side surface was cooled by applying pressured cooling air to deliver the air through the composites. The residual bending strength after the tests were measured and compared to the strength of untreated samples. The effect of cooling air flow rate on the residual bending strength was also investigated. It was showed that the bending strength was decreased by 13% after 500 thermal cycles and that the effect of the pressured cooling air on the strength was not recognized.

Fabrication of short C fiber-reinforced SiC composites by spark plasma sintering

Short carbon fiber reinforced SiC matrix composites were fabricated by spark plasma sintering. Density and mechanical properties of the composites increased continuously at increasing sintering temperature and constant pressure. Cracks in the composite matrix resulted from high thermal residual stresses generated during the cooling process from the sintering temperature due to the thermal expansion coefficient mismatch between fiber and matrix. The properties of the composites were lower than those of monolithic SiC ceramics obtained with the same processing technique as the composites. Fibers provided noncatastrophic fracture behavior of the composites as evidenced by the stress-displacement curves and fracture surface of the composites.

Behavior of two-dimensional C/SiC composites subjected to thermal cycling in controlled environments

Thermal fatigue behavior of two-dimensional carbon fiber reinforced SiC matrix composites fabricated by chemical vapor infiltration technique was investigated using an on-line quench method in controlled environments which simulated an aero-engine gas. A system of damage information acquisition (SDIA) was developed to study changes in electrical resistance of the C/SiC composites during their damage in dynamic testing. Damage to composites was assessed by the ultimate tensile strength (UTS) and SEM characterization. The results showed that: (1) under different atmosphere, the 2D-C/SiC composites subjected to thermal cycling behaved very differently and the most sensitive atmosphere was the wet oxygen; (2) external load could accelerate the degradation of the composites and changed the oxidation regimes of fibers; (3) the electrical resistance of the specimen could be detected on-line, stored in real time and analyzed reliably by the newly-developed SDIA; (4) 2D-C/SiC composites had an excellent thermal fatigue resistance in different environments.

セラミックス基繊維強化複合材料の界面接触モデルによるＦＥＭ定式化と強度シミュレーション

A new finite element model for the damage analysis of fiber-reinforced ceramics matrix composites is proposed, in which the effect of the friction of interfacial sliding after debonding between the fiber and matrix are taken into account. It is assumed that three interfacial contact states, i.e. (1) interfacial bonding, (2) interfacial sliding, and (3) interfacial sliding with fiber breakage, exist in the composite during loading. Then, stiffness matrix of each interfacial contact state is newly formulated. It was found that the number of conditional unknown displacements was always equal to that of unknown loads. Therefore, the computation can be carried out without any change in size of the structure stiffness matrix. The calculated stress distribution was characterized by that the stress recovery region along a broken fiber is composed of two different stress distributions corresponding to the bonding and debonding regions. Monte-Carlo method was taken into the proposed finite element model, and stress-strain diagrams of a carbon-coated SiC fiber reinforced SiC matrix composite were predicted by superposition method. The results show that the average strength gradually decreases with an increase in the number of fibers; the coefficient of variation decreases. Finally, the simulated stress-strain diagram was compared with probabilistic models proposed by Phoenix-Raj and Goda et al.

215 SiC 繊維強化 SiC 基複合材料の強度特性と損傷進展評価

215 SiC 繊維強化 SiC 基複合材料の強度特性と損傷進展評価

Fabrication and characterization of SiC f/SiC composite by CVI using the whiskering process

The chemical vapor infiltration (CVI) process is an effective method for fabricating SiC fiber-reinforced SiC matrix composites but it is slow with an inherent drawback of substantial residual porosity. To obtain the dense SiC f/SiC composite by the CVI process, in situ whisker growing and matrix filling (called whiskering process) was applied. The process was designed to reduce the canning effect during the CVI process and may serve to divide the large natural pores between fibers or bundles by the grown whisker and then fill the matrix inside the modified pore structure. This process was performed using MTS (CH 3SiCl 3) as a source gas and H 2 or N 2 as a diluent and the amounts of the whiskers into the matrix phases were changed by controlling the whiskering cycles. The infiltration effects, that is, increasing of the density of the SiC f/SiC composite were investigated. And the improved SiC f/SiC composites were fabricated using this process.

Tensile fracture behavior of continuous SiC fiber-reinforced SiC matrix composites at elevated temperatures and correlation to in situ constituent properties

Abstract The tensile fracture behavior and tensile mechanical properties of polymer infiltration pyrolysis (PIP)-processed two-dimensional plain-woven fabric carbon-coated Nicalon™ SiC fiber and BN-coated Hi-Nicalon™ SiC fiber-reinforced SiC matrix composites have been investigated. Tensile testing of the composites was carried out in air between 298 and 1400 K. In situ fiber strength and interface shear stress were determined by fracture mirror size and pulled-out fiber length measurements. For the Nicalon/C/SiC, tensile strength remained nearly constant up to 800 K, and while the strength dropped from 140 MPa at 800 K to 41 MPa at 1200 K, with weakest link failure mode. For the Hi-Nicalon/BN/SiC, the tensile strength increased slightly with increase in test temperature up to 1200 K; however, a large decrease in the strength was observed at 1400 K. In the case of the Hi-Nicalon/BN/SiC, the fracture was governed by fiber bundle strength. The temperature dependence of tensile strength and fracture behavior of both composites was attributed to change of the in situ constituent properties with temperature.

Pressure-Pulsed Chemical Vapor Infiltration of SiC to Three-Dimensional Carbon Fiber/SiC Preform Prepared by Polymer Impregnation and Pyrolysis.

Preforms were prepared by PIP (Polymer Impregnation and Pyrolysis) processing using polycarbosilane to 3-dimensional orthogonal weave fabrics of pitch-based carbon fiber. Porous matrices of the preforms were still more filled with β-SiC by PCVI (Pressure Pulsed Chemical Vapor Infiltration) processing using source gas mixture of SiCl4-CH4-H2 system to obtain dense 3-dimensional carbon fiber reinforced SiC matrix composites (3D-C/SiC). In the PCVI process, influence of the processing conditions on densification of the matrices was investigated in detail. The PCVI filling up to 120000 pulses were carried out under various conditions with varying temperature, residence time and gas flow rate. Then the filling-ratio was evaluated from changes in density and porosity, and crystal-phases of deposits were identified by XRD. The filling-ratio and the phase of deposits varied with the PCVI processing conditions. The PCVI processing under the conditions of 1373K in temperature, 1.5s in residence time, 4mol% each of SiCl4 and CH4 in molar-concentration and 80kPa in total pressure gave the highest filling-ratio. In this case, the number of pulses and operating time necessary for saturation of the filling-ratio were 60000 pulses and 192ks, respectively. The porosity of the densest composite was about 6% from macrosurface to 0.5mm in depth and less than 9% even to 1.5mm in depth. Also, it was found that higher total pressure was effective for increasing filling-speed without increasing the porosity, but disadvantageous in the consumption of the source gases.

Effects of coating treatment on mechanical properties of carbon fibres and reinforced silicon carbide composites

Three-dimensionally braided carbon fibre reinforced SiC matrix composites have been fabricated and the effects of coating treatment on the mechanical properties have been investigated. It has been found that pyrocarbon coating can improve the strength of the heat treated carbon fibres. When the coating thickness was 0.5 m, the composites had better mechanical properties: a flexural strength of 643 MPa and a fracture toughness of 17.9 MPa m12. The composites also exhibited a toughening fracture mode.

Microstructure and mechanical properties of low-activation glass-ceramic joining and coating for SiC/SiC composites

Calcia-alumina (CA) glass-ceramic was studied as a candidate low-activation joining and sealing material for SiC/SiC components for fusion blanket and diverter structures, in terms of microstructural stability and mechanical properties. The CA glass-ceramic joining and seal coating were applied to the Hi-Nicalon™ SiC fiber-reinforced SiC matrix composites in which the matrix had been formed through chemical vapor infiltration and polymer impregnation and pyrolysis methods. Microstructural characterization was carried out for the joined and coated materials by optical and scanning electron microscopy (SEM). The mechanical property of the joint was evaluated through a shear test on sandwich joints. The average shear strength of the joined structures was 28 MPa at room temperature. Fractography revealed that the fracture occurred in the glass phase and the shear strength may be improved by reduction of the glass fraction.

Critical issues and current status of SiC/SiC composites for fusion

SiC fiber-reinforced SiC matrix composites (SiC/SiC) are being considered as a candidate structural material for fusion reactors because of their low induced radioactivity by 14 MeV neutron irradiation and high-temperature strength. Material development of SiC/SiC composites, including SiC fiber, matrix and interphase processing for fusion reactor applications, has been under investigation for several years. The purpose of this paper is to present an overview of current research in material development, properties and irradiation response of new SiC/SiC composites. Several technologically critical issues to be solved for fusion applications, such as irradiation resistance, thermal properties, environmental effects, hermeticity, joining technique and protective coating are also reviewed.