Fiber-reinforced SiC Matrix Composites Research Articles

Effect of heat treatment on the mechanical properties of PIP–SiC/SiC composites fabricated with a consolidation process

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been considered as candidates for heat resistant and nuclear materials. Three-dimensional (3D) SiC/SiC composites were fabricated by the polymer impregnation and pyrolysis (PIP) method with a consolidation process, mechanical properties of the composites were found to be significantly improved by the consolidation process. The SiC/SiC composites were then heat treated at 1400°C, 1600°C and 1800°C in an inert atmosphere for 1h, respectively. The effect of heat treatment temperature on the mechanical properties of the composites was investigated, the mechanical properties of the SiC/SiC composites were improved after heat treatment at 1400°C, and conversely decreased with increased heat treatment temperature. Furthermore, the effect of heat treatment duration on the properties of the SiC/SiC composites was studied, the composites exhibited excellent thermal stability after heat treatment at 1400°C within 3h.

Continuous SiC Fibre-Reinforced SiC Matrix Composites: An Analysis Based on Patents

Over 1800 SiCf/SiC patents have been searched and identified in this work. SiCf/SiC technologies are emerging rapidly from 2005 in China. However, the extremely low proportion of patents owned by companies indicates that more effort and focus on SiCf/SiC are extremely needed to enable industrial application. Statistical results of worldwide patents reveal that the modification of the mechanical properties is the most urgent demand in industry; meanwhile, the analysis results show that the CVI/CVD (chemical vapor infiltration /chemical vapor deposition) method appears promising to enhance the mechanical properties, as well as to improve the thermal conductivity and stability, to lower the costs and to enhance the controllability of the product.

Preparation of Carbon Fiber Reinforced SiC Matrix Composites by PIP Process

The precursor infiltration pyrolysis technology for preparation of ceramic matrix composites (CMCs) is both flexible and tailorable to shape and engineering requirements. During sintering process, PCS experienced an organic–inorganic transformation and acted as the bonding material between Carbon fiber. Compare to PCS, the ceramic conversion rate of PCS-DVB increased to 70-75%, the main reaction zone temprerature reduced to 400-800°C, which is in favor of protecting carbon fiber.

Au ion irradiation of various silicon carbide fiber-reinforced SiC matrix composites

Silicon carbide fiber-reinforced SiC matrix composites are promising candidates as fuel cladding for several concepts of Generation IV reactors and as structural materials for fusion reactors. The composites used in this study were composed of a SiC matrix obtained by chemical vapor infiltration associated with various fiber types (Tyranno Type-S, Tyranno SA Grade-3 and Hi-Nicalon Type-S) and with a PyC layer as the interphase. 12MeV Au ions were used for irradiation up to 0.05 and 1 displacement per atom (dpa) fluences at room temperature and 800°C. Analysis of both microstructure and composition of composites were performed by scanning electron microscopy (SEM), electron probe microanalysis and Raman spectroscopy. At room temperature and low fluence, Raman spectroscopy results showed that irradiation induces a disordered/distorted state into fibers and matrix. With increasing fluence, a total amorphization of these constituents occurs. The increase in the irradiation temperature leads to a damage recovery and partial recrystallization of samples. Image analysis performed from SEM micrographs highlights no significant change in fiber diameter and shape. However, SEM analysis suggests a longitudinal shrinkage of Tyranno Type-S fibers for the composite irradiated at 1dpa at room temperature and 800°C. These results are in complete agreement with conclusions from neutron irradiations suggesting an appropriate relevance of irradiations with 12MeV Au.

Determination of interfacial mechanical properties of ceramic composites by the compression of micro-pillar test specimens

A novel method to determine the fiber-matrix interfacial properties of ceramic matrix composites is proposed and evaluated; where micro-pillar samples containing inclined fiber/matrix interfaces were prepared from a SiC fiber-reinforced SiC matrix composites and then compression-tested using the nano-indentation technique. This new test method employs a simple geometry and mitigates the uncertainties associated with complex stress state in the conventional single-filament push-out method or tensile unloading–reloading hysteresis loop analysis method for the determination of interfacial properties. Based on the test results using samples with different interface orientations, the interfacial debond shear strength and the internal friction coefficient are explicitly determined and compared with values obtained by other test methods. SEM observation showed that micro compression caused an adhesive type of debonding between the fiber and the pyrolytic carbon interface. The results suggest that the debonding/failure behavior of the micro-pillars followed the Coulomb fracture criterion. The determined interfacial debond shear strength is ~100 MPa, which appears to be smaller than that determined from fiber push-out test for similar composite systems. The difference can be explained by the effect of normal stress (clamping stress) on the apparent interfacial debond shear strength.

Highly efficient densification of carbon fiber-reinforced SiC-matrix composites by melting infiltration and pyrolysis using polycarbosilane

Abstract Carbon fiber-reinforced SiC-matrix composites (C f /SiC) were fabricated via a precursor infiltration and pyrolysis (PIP) process. A polycarbosilane (PCS) precursor was used, with a halogen element (iodine) for curing. The effects of high-temperature polycarbosilane infiltrate melting and iodine-based curing on the efficiency of the PIP process, as well as the physical characteristics of the fabricated C f /SiC composites, were investigated. Highly dense C f /SiC composites with strong fiber/matrix interfacial bonding were fabricated. By melting the infiltrate and using iodine-based preform curing, the ceramic yield of polycarbosilane increased drastically from 38 wt% to 82 wt%. This increase, which is due to pyrolysis, resulted in a low degree of shrinkage in the polycarbosilane-derived matrix. This shrinkage, in turn, increased the density of the C f /SiC composites and improved the interfacial bonding between the matrix and fibers. As a result, the fabricated C f /SiC composites exhibited a density of 1.75 g/cm 3 . This was much higher than the 0.38 g/cm 3 density of bare carbon fiber preforms after 6 iterations of the PIP process.

Effect of heat treatment on microstructure and mechanical properties of PIP-SiC/SiC composites

Continuous SiC fibre reinforced SiC matrix composites (SiC/SiC) have been studied as materials for heat resistant and nuclear applications. Thermal stability is one of the key issues for SiC/SiC composites. In this study, 3D SiC/SiC composites are fabricated via the polymer impregnation and pyrolysis (PIP) process, and then heat treated at 1400°C, 1600°C and 1800°C in an inert atmosphere for 1h, respectively. The effect of heat treatment on microstructure and mechanical properties of the composites is investigated. The results indicate that the mechanical properties of the SiC/SiC composites are significantly improved after heat treatment at 1400°C mainly because the mechanical properties of the matrix are greatly improved due to crystallisation. With the increasing of heat treatment temperature, the properties of the composites are conversely decreased because of severe damage of the fibres and the matrix.

Dielectric properties of SiC fiber-reinforced SiC matrix composites in the temperature range from 25 to 700 °C at frequencies between 8.2 and 18 GHz

The complex permittivity of a SiC fiber-reinforced SiC matrix (SiCf/SiC) composite was measured in a temperature range of 25–700°C at frequencies from 8.2 to 18GHz. The SiCf/SiC composite exhibited a positive temperature coefficient, that is, its complex permittivity increased with temperature. The observed positive temperature coefficient can be interpreted by Debye theory, by which the theoretical predictions were in well agreement with the experimental results.

The Pyrolysis Processing of Polycarbosilane Studied by TG, XRF, IR, XRD, and XPS

Polycarbosilane (PCS) is one of precursor systems applied in industry for the Polymer Infiltration Pyrolysis (PIP) processing of C or SiC fiber reinforced SiC matrix composites (Cf/SiC or SiCf/SiC CMC) materials. In this work, a series of PCS-derived SiC specimens treated at 300, 550, 800, and 1100 °C was studied by XRF, IR, XRD and XPS methods. The results show that a slight amount of PCS molecules with low softening point evaporates below 300 °C; the cross-link between PCS chains takes place to form a 3D -Si-C-Si- network via the reaction between -Si-CH3, -Si-CH2-Si- and -Si-H groups in the temperature range of 300-550 °C; an amorphous phase of SiC was observed when PCS was heated up to 800 °C, which indicates the completion of transformation from organic to inorganic; above 800 °C, β-SiC domain grows. Furthermore, a surface structure evolution of PCS-derived SiC specimens with temperature is proposed after the analyzing the XPS spectra.

Mechanical Properties of Short Carbon Fiber-Reinforced SiC-Matrix Composites and Correlation to Fibers

PAN and Pitch short carbon fiber-reinforced SiC matrix composites were fabricated by using a melting infiltration technique. The microstructure of the composites was characterized by scanning electron microscopy. The flexural strength of the composites was measured at room and high temperatures. The thermal conducitivity of the composites were evaluated. Effects of fibers on mechanical properties and thermal conductivity were assessed. The experimental results showed that the silicification of fibers during siliconizing was prevented due to the presence of barrier layer on the surface of fiber. Also, flexural strength and thermal conductivity depended on fibers used and content of fibers.

Microstructure and thermal shock property of liquid phase sintered Cf/SiC composites

This paper dealt with a liquid phase sintering process for the fabrication of carbon fiber reinforced SiC matrix composites (Cf/SiC), using a ultra-fine SiC particles and oxide additive materials. Especially, the thermal shock properties of Cf/SiC composites were investigated at the elevated temperatures. The characterization of monolithic SiC materials by the variation of starting SiC particle size was also examined. Monolithic SiC materials possessed an excellent density higher than about 3.0mg/m3 and a good flexural strength of about 700MPa, regardless of starting SiC particle size. Cf/SiC composites also represented a dense morphology in the intra-fiber bundle region, even if there were some amount of pores. However, the flexural strength of Cf/SiC composites greatly decreased at the thermal shock temperature of 400°C.

Mechanical and microwave dielectric properties of SiCf/SiC composites with BN interphase prepared by dip-coating process

Abstract The BN interphase of SiC fiber-reinforced SiC matrix (SiCf/SiC) composites was fabricated by dip-coating process with boric acid and urea as precursor. The results show that the tensile strength of SiC fiber decreases about 30% after BN coating treatment, but the BN coating has little influence on the electrical resistivity of SiC fiber. Compared with the as-received SiCf/SiC composites, the SiCf/SiC composites with BN interphase exhibit a toughened fracture behavior, and the flexural strength is about 2 times that of the as-received SiCf/SiC composites. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in weakening interfacial bonding, which can improve the mechanical properties of SiCf/SiC composites remarkably. Owing to the close dielectric properties between SiC and BN, the complex permittivity of SiCf/SiC composites with and without the BN interphase is similar.

A STUDY ON DYNAMIC BEHAVIOR OF Cf/SiC COMPOSITES

The dynamic behavior for the fabrication of carbon fiber reinforced SiC matrix composites( C f / SiC ) is investigated by the theory and experiment. The governing differential equation of a composite beam is derived via Hamilton's principle. The C f / SiC composites have been fabricated by a liquid phase sintering process, using the ultra-fine SiC particles and oxide additive materials. The SiC based materials are fabricated by using a commercial SiC powder with an average size of about 0.3µm. An Al 2 O 3- Y 2 O 3- SiO 2 powder mixture is used as a sintering additive. The compositional ratio ( Al 2 O 3/ Y 2 O 3) and its total amount ( Al 2 O 3+ Y 2 O 3) of additive materials are 1.5 and 10 wt%, respectively. Especially, the content of PVB is changed from 0 wt% to 10 wt%. The SiC based materials are sintered at the temperature of 1820°C under 30 MPa for 1 hr. In this study, the effect of content of PVB on the natural frequency and mode shape is obtained. Finally, the relationship between natural frequency and mechanical property of C f / SiC composites is discussed.

Al Ion Implantation of SiC Coated Carbon Fiber-Reinforced SiC Matrix Composites by Metal Vapor Vacuum Arc Ion Source

SiC coated carbon fiber-reinforced SiC matrix (C/SiC) composites were implanted with aluminum ions by metal vapor vacuum arc ion source to improve their oxidation resistance. Depth profile of the aluminum ions in the SiC coated C/SiC composites was checked by Auger electronic energy spectrum. Oxidation tests were performed in flowing dry air at 1300°C on the SiC coated C/SiC composites. The samples with ion implantation exhibited lower weight loss than those without aluminum ion implantation. The surface morphologies of the samples were obtained by scanning electronic microscope. As compared with the mechanical properties of the samples without ion implantation, those of ion-implanted samples changed little.

SiCf/SiC 복합체의 특성에 미치는 열간가압소결 조건의 영향

Continuous SiC fiber-reinforced SiC-matrix composites (SiC f /SiC) had been fabricated by electrophoretic infiltration combined with ultrasonication. Nano-sized β-SiC added with 12 wt% of Al 2 O 3 -Y 2 O 3 additive and Tyranno TM -SA3 fabric were used as a matrix phase and fiber reinforcement, respectively. After hot pressing at 5 different conditions, the density, microstructure and mechanical properties of SiC f /SiC were characterized. Hot pressing at relatively severe conditions, such as 1750℃ for 1 and 2 h, resulted in a brittle fracture behavior due to the strong fiber-matrix interface in spite of their high flexural strength. On the other hand, toughened SiC f /SiC composite could be achieved by hot pressing at milder condition because of the formation of weak interface in spite of the decreased flexural strength. These results proposed the importance of weak fiber-matrix interface in the fabrication of ductile SiC f /SiC composite.

Oxidation of SiC Fiber-Reinforced SiC Matrix Composites with a BN Interphase

The oxidation kinetics of SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) and the constituent fibers was characterized by thermogravimetric analysis and microstructural characterization at temperatures (816-1538°C) and oxygen partial pressures (0.1% to 5% O2) relevant to the hypersonic flight and re-entry environments. TGA of the SiC fibers showed that oxidation of the thin BN surface layer led to initially rapid oxidation kinetics and formation of a relatively thick silica scale at very short times under most test conditions. At longer times the fiber oxidation kinetics were representative of silica formation on pure SiC. Oxidation of the composites was conducted on coupons with the SiC seal coat removed on one edge to simulate damage to the composite, allowing ingress of oxygen to the fiber tows. Microscopy was conducted to determine the distance of oxygen ingress into the coupon. At the lower temperatures and oxygen partial pressures the exposed edge did not seal off by silica formation, yet the BN interphase areas were only minimally oxidized. At the intermediate temperatures silica formed at the exposed surface limiting further oxidation of the exposed fibers and BN interphase areas. Finally at the highest temperature and lowest oxygen partial pressure, active oxidation of SiC occurred for both the fibers and coupons resulting in irregular material attack. Implications for use of SiC/BN/SiC materials for hypersonic vehicle thermal protection systems are summarized.

Stress-dependence and time-dependence of the post-fatigue tensile behavior of carbon fiber reinforced SiC matrix composites

The major objective of this paper is to phenomenally report the stress-dependence and time-dependence of fatigue damage to C/SiC composites, and to tentatively discuss the effects of the fatigue stress levels and the fatigue cycles on the post-fatigue tensile behavior. Results show that compared with the virgin strength of the as-received C/SiC specimens, the tensile strengths of the as-fatigued specimens after 86,400 cycles were increased by 8.47% at the stresses of 90 ± 30 MPa, 23.47% at 120 ± 40 MPa, and 9.8% at 160 ± 53 MPa. As cycles continued, however, the post-fatigue strength of the composites gradually decreased after the peak of 23.47%, at which the optimal strength enhancement was obtained because the mean fatigue stress of 120 MPa was the closest to thermal residual stress (TRS), and caused TRS relieve largely during the fatigue. Most interestingly, there was a general inflexion appeared on the post-fatigue tensile stress–strain curves, which was just equal to the historic maximum fatigue stress acted upon the as-fatigued specimens. Below this inflexion stress the tensile curves revealed the apparent linear behavior with little AE response, and above that nonlinearity with new damage immediately emitted highly increase rate of AE activities. This ‘stress memory’ characteristic was strongly relevant to damaged microstructures of the as-fatigued composites in the form of the coating/matrix cracks, interface debonding/wear, and fiber breaking, which resulted undoubtedly in reduction of modulus but in proper increase of strength via TRS relief.

Fabrication Processing and Evaluation on Thermal Shock Damage of C/SiC Composite

Carbon fiber reinforced SiC matrix composites (C/SiC) is one of attractive candidates in the ultrahigh temperature components such as turbine rotor and internal combustion part. The objective of this paper is to investigate the characterization of C/SiC composite containing nano scale SiC powder. Especially, the effects of thermal characteristics and thermal shock damage on the C/SiC composite using nondestructive technique were evaluated in detail because the composite is expected to be used in the conditions of high temperature. The C/SiC composite was fabricated by a liquid phase sintering (LPS) process with commercial SiC powder of about 30nm. The matrix region for C/SiC composites prior to the sintering were prepared by a slurry infiltration technique. The composite material was consolidated at the temperature of 1820°C, pressure of 20MPa and 2hours holding time in hot press, respectively. The fractured surfaces of C/SiC composites were also observed to examine the fracture profile of fiber bundle region and the adhesion between carbon fabric and matrix. The parameters such as velocity and attenuation ratio of ultrasonic wave were used to evaluate nondestructively the degree of damage of the composite underwent cyclic thermal shock.

액상소결 시의 β-SiC의 입자성장 방지

In our previous studies, continuous SiC fiber-reinforced SiC-matrix composites (SiCf/SiC) had been fabricated by two different slurry infiltration methods: vacuum infiltration and electrophoretic deposition (EPD). 12 wt% of Al₂O₃-Y₂O₃-MgO with respect to SiC powder was used as additives for liquid-phase assisted sintering. After hot pressing at 1750°C under 20MPa for 2 h in Ar atmosphere, a high composite density could be achieved for both cases, whereas the problems such as large grain size and non-uniform distribution of liquid phase were observed, which was resulted in the relatively poor mechanical properties of composites. Therefore, efforts have been made to reduce the grain growth during the sintering, including the optimization for hot pressing condition and utilization of spark plasma sintering using a SiC monolith. Based on the results, spark plasma sintering was found to be effective method in decreasing the amount of sintering additive, time and grain growth, which will be explained in comparison to the results of hot pressing in this paper.

Deposition of BN interphase coatings from B-trichloroborazine and its effects on the mechanical properties of SiC/SiC composites

Boron nitride thin films were deposited on silicon carbide fibers by chemical vapor deposition at atmospheric pressure from the single source precursor B-trichloroborazine (Cl 3B 3N 3H 3, TCB). The film growth and structure, as a function of deposition temperature, hydrogen gas flow rate, and deposition time, were discussed. The deposition rate reaches a maximum at 1000 °C, then decreases with the increasing of temperature, and the apparent activation energy of the reaction is 127 kJ/mol. Above 1000 °C, gas-phase nucleation determines the deposition process. The deposited BN films were characterized by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of BN interphase on the mechanical properties of the unidirectional SiC fiber-reinforced SiC matrix (SiC/SiC) composites was also investigated. The results show that the flexural strength of SiC/SiC composites with and without coating is 276 MPa and 70 MPa, respectively, which indicates that BN interphase coating deposited from B-trichloroborazine precursor can effectively adjust the fiber/matrix interface, thus causing a dramatic increase in the mechanical properties of the composites.