Continuous Silicon Carbide Fiber Research Articles

Long-time oxidation resistance of KD-SiC fibers with different composition and structure in air atmosphere

Continuous silicon carbide (SiC) fibers, as reinforcement of ceramic matrix composites, have broad application prospects in the fields of aviation, aerospace and nuclear energy. Three typical KD-SiC fibers were adopted to explore the relationship of the composition and structure with their long-term oxidation (1–100 h) resistance in air environment. The mechanical strength retention of the nearly stoichiometric polycrystalline SiC fiber (C-1) was generally higher than that of the SiC fiber (C-3) with excess carbon and low oxygen, also higher than the nearly stoichiometric SiC fiber (C-2), especially under oxidation conditions of higher temperature and longer holding time. By comparing the high-temperature resistance with oxidation resistance at 1200–1600 °C, it was found that the oxidation reaction was the dominant factor affecting the mechanical properties. This work could provide theoretical and practical references for improvement of oxidation resistance of SiC fibers and their composites.

Emerging continuous SiC fibers for high-temperature applications

Silicon carbide (SiC) fibers are responsible for the ultimate strength and toughness of SiC-fiber reinforced composites in harsh environments. The development of a new generation of continuous SiC fibers continues to advance the mechanical properties of composite materials. Tyranno™ SA4 fiber was recently released as a successor of Tyranno™ SA3 fiber. Laser-driven chemical vapor deposition (LCVD) has been adopted as an alternative fiber processing route to synthesizing high-strength SiC fiber with tailorable small diameters and chemical compositions. Both Tyranno™ SA4 and laser-driven CVD fibers show very high tensile strength, about 4 GPa in the as-fabricated condition. The degradation of thermal stability and strength due to annealing in an inert environment were similar for Tyranno™ SA3 and SA4 fibers because of their similar carbon-rich, crystalline microstructure. Silicon-rich fibers produced by LCVD possessed heterogeneous crystallinity, which was attributed to laser power distribution and showed microstructural instability at 1500 °C and above. The new SiC fibers demonstrated an increase in as-fabricated strength but faced the same challenges in environmental resistance as the traditional SiC fibers do.

Folding endurance of continuous silicon carbide fibres: A comparative study

The limited folding resistance of continuous silicon carbide (SiC) fibres hinders their application as flexible, foldable materials. With this objective in mind, the folding endurance and damage properties of the second (2nd) and third (3rd) generation continuous SiC fibre tows were investigated through repeated folding tests, optical microscope observation and tensile tests. These SiC fibre tows were disassembled from two-dimensional (2D) SiC fibre braided fabrics with varying braiding angles. The braiding process can alleviate the force on fibre tows during the textile forming process. The investigation of damage mechanisms and analysis of force conditions are instrumental in optimizing structural parameters. The research findings suggested that, in comparison to the 3rd generation continuous SiC fibres, the 2nd generation SiC fibre tows demonstrated higher resistance to repeated folding. In contrast, the 2nd generation fabrics exhibited slightly lower folding endurance values. After repeated folding, the SiC fibre tows in fabrics showed the highest strength losses near the braiding angle of 37.8? to 38.3?. In comparison, the SiC fibre fabric demonstrated the lowest folding endurance values (approximately 760 times) near the braiding angle of 41? to 42?. Considering factors such as folding endurance value, the strength loss rate of fibre tows and fabric strength loss rate, it can be concluded that SiC fibres in fabrics with large braiding angles exhibit optimal performance in terms of folding endurance.

Effect of CaO doping on the properties and crystallization behavior of Y2O3–Al2O3–SiO2 glass

Nowadays, Y2O3–Al2O3–SiO2 (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y2Si2O7, mullite, and SiO2 (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization.

Microstructural evolution of polymer derived SiC ceramics and SiC/SiC composite under 1.8MeV electron irradiation

Continuous silicon carbide fiber reinforced silicon carbide matrix composites (SiC/SiC) are promising candidate materials for nuclear applications. Herein, SiC ceramics and SiC/SiC composite were prepared by a polymer deriving method, and irradiated using a 1.8 MeV electron beam. The microstructural evolution and radioluminescence performance were investigated, and the results showed that the SiC ceramics and the SiC/SiC composite all exhibited evident amorphization after the electron irradiation. In addition, the radioluminescence intensity of the SiC ceramics and the SiC/SiC composite was too low owing to the self-absorption of the free carbon in the polymer derived SiC ceramics.

Review on thermal conductivity of SiCf/SiC composites for nuclear applications

Continuous silicon carbide fibre toughened silicon carbide composites (SiCf/SiC) are highly promising materials for nuclear reactor applications due to their low chemical activity, low density, low coefficient of thermal expansion, high energy conversion rate and good high temperature strength. However, the thermal conductivity requirements of nuclear reactors are difficult to meet in conventional SiCf/SiC composites. To improve the thermal conductivity of SiCf/SiC composites, many approaches to enhance the thermal conductivity of SiCf/SiC composites under nuclear reactor applications were firstly introduced. Further, the worldwide research process in this field has been reviewed. Finally, further development of the thermal conductivity research was discussed and prospected.

Microstructure and mechanical properties of SiCf/SiC composite prepared by chemical vapor infiltration

Continuous silicon carbide (SiC) fiber reinforced SiC ceramic matrix (SiCf/SiC) composites are widely studied for possible applications as hot sections in next-generation aeroengines because of their excellent thermo-structural properties. Their mechanical properties were comprehensively evaluated based on the interaction mechanisms among fiber, interphase, and matrix. Moreover, it was found that matrix cracking and fiber bridging mechanisms influenced the shear-dominated and tension-dominated properties, respectively, clearly indicating that the mechanical properties of the material should be correlated. In this study, mechanical properties of the two-dimensional SiCf/SiC composite were comprehensively evaluated, and the correlation laws were verified between tension and bending, tension and in-plane shear, and in-plane shear and interlaminar shear. Results showed that the ratio of shear to tensile matrix cracking stress was 0.68, while the ratio of flexural to tensile strength was 2.3, and the interlaminar shear strength was equal to the in-plane shear strength minus the fiber bridging stress. Fiber bridging is the key mechanism controlling the above-mentioned correlation by the established meso-mechanical formulas, and the interlaminar shear mechanism is controlled by matrix cracking and influenced by interlaminar pores.

Mechanical property of Pyro-Carbon coated SiC fibers fabricated by continuous chemical vapor deposition method

PurposeA continuous chemical vapor deposition (CVD) method has been used to fabricate pyro-carbon (PyC) coating on continuous silicon carbide (SiC) fibers. The paper aims to evaluate these coated fibers by testing filament tensile and using microstructure characterization.Design/methodology/approachThe continuous SiC fiber-reinforced SiC matrix (SiC/SiC) composite is widely studied in aerospace and nuclear applications. The PyC is the probable option in fusion and fast reactor. However, the conventional fabrication method of PyC coating has some drawbacks influencing performance and efficiency.FindingsThe results showed that PyC-coated SiC fibers with continuous CVD method are more straight than conventional ones and residual deformations could not be observed, and these PyC coatings have complete geometry and uniform thickness. In different process conditions, the thickness of PyC coating could control from ∼100 to ∼1,000 nm.Originality/valueThe coated SiC fibers in a lower gas ratio (1:7 to 1:3), lower pressure (500–1,000 Pa) and appropriate winding speed (3 to 5 rpm) have relative high filament tensile strength (∼3.5 to ∼3.9 GPa). And the strength of coated SiC fibers has a negative correlation with the measured thickness of PyC coating. A distinctive growth process was discovered in the continuous CVD method. In a certain range, the quicker growing rate of PyC is obtained in shorter deposition time which means an efficient and quality method could be applied to fabricate coatings.

Microstructural and mechanical evolution of SiCf/SiC composites in wet oxygen atmosphere above 1000 °C

As thermal-structural materials used in gas turbine hot sections, continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites serve under high temperature gas steam corrosion. Therefore the long-term durability of the composites is strongly dependent on the microstructural and mechanical stability under the corrosion. Here, the microstructural and mechanical evolution of SiCf/SiC were investigated in a simulated steam environment (22 vol% H2O + 78 vol% O2, 1100–1300 °C). The results indicate that the temperature plays a major role in the corrosion of the composites. As the temperature rises up to 1200 °C, the fiber/matrix interphase (boron nitride) is completely dissipated due to oxidation. Meanwhile, a dense SiO2 scale forms on the composite surface and cristobalite phase tends to precipitate with the increase of temperature. The dissipation of interphase can lead to significant mechanical degradation on the composites. Furthermore, the degradation mechanism was also proposed in terms of stress distribution and fracture morphology. This study can offer new insight for understanding the wet-oxygen corrosion of SiCf/SiC and thus constructing SiCf/SiC with high stability in gas steam.

High-temperature mechanical properties and oxidation resistance of SiCf/SiC ceramic matrix composites with multi-layer environmental barrier coatings for turbine applications

Continuous silicon carbide fiber reinforced silicon carbide (SiCf/SiC) ceramic matrix composites are considered promising materials as high-temperature components of advanced aero-engines. However, due to their susceptibility to oxidation and corrosion at high temperature, environmental barrier coatings (EBCs) must be applied on the surface of SiCf/SiC. In this study, Si/Y2SiO5/LaMgAl11O19 (LMA) multi-layer EBCs were fabricated to protect SiCf/SiC by using atmospheric plasma spraying (APS). The high-temperature tensile fatigue performance of SiCf/SiC with and without EBCs was evaluated. The results indicated that EBCs significantly improved the tensile fatigue properties of SiCf/SiC at high temperature in air atmosphere. Meanwhile the bending strength of specimens after isothermal aging or not was also tested. The multi-layer EBCs in this study may be a promising EBCs system for SiCf/SiC after some improvements.

Insight into microstructural architectures contributing to the tensile strength of continuous W-core SiC fiber

The properties of CVD silicon carbide (SiC) fiber are closely correlated with its complex microstructure; however, the microstructural architectures contributing to its strength are not well understood. Here, two kinds of W-core SiC fibers (SiC-3200 and SiC-3800) coated with same C coating, possessing different tensile strength and discrepant microstructure in SiC portion, were fabricated by controlling deposition temperature during CVD process. The structure discrepancy contributing to the different tensile strength for both SiC fibers were explored by the combined Raman spectra, EPMA, SEM and HRTEM. It is revealed the high-crystallinity β-SiC columnar grains in the inner zone always evolve into a higher disorder character yet involving partial surviving columnar grains toward surface for both SiC fibers. However, as compared with SiC-3800 fiber, the slightly higher C over-stoichiometric composition yields lower-crystallinity SiC columnar grains across the radius for SiC-3200 fiber, further resulting in lower strength via forming smoother stepped fracture morphology.

Development of Continuous Silicon Carbide Fibers Nicalon and Hi-Nicalon for High Temperature Composite Applications

Development of Continuous Silicon Carbide Fibers Nicalon and Hi-Nicalon for High Temperature Composite Applications

The effects of preparation temperature on the SiCf/SiC 3D4d woven composite

Continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites have promising applications in aero-engine due to their unique advantages, such as low density, high modulus and strength, outstanding high temperature resistance and oxidation resistance. As SiC fibers are main reinforcements in SiCf/SiC composites, the crystallization rate and initial damage degree of SiC fibers are seriously influenced by preparation temperatures of SiCf/SiC composites, namely mechanical properties of SiC fibers and SiCf/SiC composites are influenced by preparation temperatures. In this paper, KD-II SiC fibers were woven into 3D4d preforms and SiC matrix was fabricated by PIP process at 1100 °C, 1200 °C, 1400 °C and 1600 °C. Digital image correlation (DIC) method was adopted to measure the uniaxial tensile properties of these SiCf/SiC composites. In addition, finite element method (FEM) based on representative volume element (RVE) was adopted to predict the mechanical properties of SiCf/SiC composites. The good agreements between numerical results and experimental results of uniaxial tensile tests verified the validity of the RVE. In last, the transverse tensile, transverse shear, uniaxial shear properties were predicted by this method. The predicted results illustrated that axial tensile, transverse tensile and axial shear properties were greatly influenced by the preparation temperatures of SiCf/SiC composites while transverse shear properties were not significantly various. And the mechanical properties of SiCf/SiC composites peaked at 1200 °C among these four temperatures while their values reached their lowest points at 1600 °C because of thermal damage and brittle failure of SiCf/SiC composites.

Preparation of SiCf/SiC Composites with Low Porosity by Liquid Composite Moulding-Pyrolysis Process

Traditionally, Polymer infiltration and pyrolysis (PIP), chemical vapor infiltration (CVI) and melt infiltration (MI) are main processes to fabricate continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites, one of attractive potential high temperature structural materials. However, long preparation period and high porosity are still problems for further applications. Especially, porosity is crucial to the mechanical properties. Liquid composite moulding-pyrolysis (LCMP) used liquid SiC precursor to decrease the open porosity to 5% with no more than 11 cycles of infiltration and pyrolysis. Mechanical properties like bending strength was investigated with different thickness of pyrolitic carbon (PyC) interface and pyrolysis cycles. The bending strength reached 585 MPa with 200 nm PyC interface under 1200°C pyrolysis temperature. Thus, LCMP process offers exciting opportunities to improve performance of SiCf/SiC composites.

Development of non-brittle fracture in SiCf/SiC composites without a fiber/matrix interface due to the porous structure of the matrix

Silicon carbide (SiC) porous-matrix composites lacking a fiber/matrix interface and incorporating continuous unidirectional SiC fibers as reinforcements were developed using sandwiched layers with non-infiltration fiber bundles and a porous matrix in a laminate to achieve crack deflection. Excellent control of the porosity was achieved by varying the amount of carbon powder added. The matrix porosity was characterized in terms of its microstructure and mechanical properties. The SiC porous-matrix composite with an open porosity of 22%, which was formed with 40 vol% carbon powder, had a flexural strength of 253 ± 31 MPa and exhibited non-brittle fracture behavior up to a stress maximum, followed by a gradual depletion of the fracture energy, decreasing the stress on continued deformation. Significant changes in the mechanical properties, such as the flexural strength and fracture energy, of the fabricated SiC porous-matrix composite were not observed following exposure to air at high temperature (up to 1100 °C).

KD-S SiCf/SiC composites with BN interface fabricated by polymer infiltration and pyrolysis process

Continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites are attractive candidate materials for aerospace engine system and nuclear reactor system. In this paper, SiCf/SiC composites were fabricated by polymer infiltration and pyrolysis (PIP) process using KD-S fiber as the reinforcement and the LPVCS as the precursor, while the BN interface layer was introduced by chemical vapor deposition (CVD) process using borazine as the single precursor. The effect of the BN interface layer on the structure and properties of the SiCf/SiC composites was comprehensively investigated. The results showed that the BN interface layer significantly improved the mechanical properties of the KD-S SiCf/SiC composites. The flexure strength and fracture toughness of the KD-S SiCf/SiC composites were evidently improved from 314±44.8 to 818±39.6 MPa and 8.6± 0.5 to 23.0±2.2 MPa·m1/2, respectively. The observation of TEM analysis displayed a turbostratic structure of the CVD-BN interface layer that facilitated the improvement of the fracture toughness of the SiCf/SiC composites. The thermal conductivity of KD-S SiCf/SiC composites with BN interface layer was lower than that of KD-S SiCf/SiC composites without BN interface layer, which could be attributed to the relative low thermal conductivity of BN interface layer with low crystallinity.

Effects of silicon ion irradiation on the interface properties of SiCf/SiC composites

Continuous silicon carbide fiber–reinforced silicon carbide matrix composites (SiCf/SiC) are promising candidate materials for nuclear applications. In this paper, three–dimensional SiCf/SiC composites were fabricated using polymer infiltration and pyrolysis method. Interface properties of SiCf/SiC composites that were irradiated with 3MeV Si ions to 1dpa and 5dpa at room temperature were studied using single-fiber push–out test, Raman spectroscopy, and transmission electron microscopy. Results indicate that, after being irradiated with different doses of Si ions, SiCf/SiC composites have weaker interfacial shear strength compared to that of samples before irradiation. The greater that the ion irradiation damage is, the lower that the interfacial shear strength is. With an increase in ion irradiation dose, the strength of the disordered (D) and graphitic (G) characteristic peaks in Raman spectra of SiCf/SiC composite decreases, and full width at half–maximum broadens. TEM micrographs show that ion irradiation damaged the continuity of SiCf/SiC composites, and microcracks appeared at pyrocarbon interface between the fiber and matrix. The crystallinity of SiC was lowered, the grain size shrank, and the ordered C phase became amorphous noncrystalline structure.

Effect of oxidation treatment on KD–II SiC fiber–reinforced SiC composites

Abstract Continuous silicon carbide fiber–reinforced silicon carbide matrix (SiC f /SiC) composites have developed into a promising candidate for structural materials for high–temperature applications in aerospace engine systems. This is due to their advantageous properties, such as low density, high hardness and strength, and excellent high temperature and oxidation resistance. In this study, SiC f /SiC composites were fabricated via polymer infiltration and pyrolysis (PIP) with the lower–oxygen–content KD–II SiC fiber as the reinforcement; a mixture of 2,4,6,8–tetravinyl–2,4,6,8–tetramethylcyclotetrasiloxane (V4) and liquid polycarbosilane (LPCS), known as LPVCS, was used as the precursor; while pyrolytic carbon (PyC) was used as the interface. The effects of oxidation treatment at different temperatures on morphology, structure, composition, and mechanical properties of the KD–II SiC fibers, SiC matrix from LPVCS precursor conversion, and SiC f /SiC composites were comprehensively investigated. The results revealed that the oxidation treatment greatly impacted the mechanical properties of the SiC fiber, thereby significantly influencing the mechanical properties of the SiC f /SiC composite. After oxidation at 1300 °C for 1 h, the strength retention rates of the fiber and composite were 41% and 49%, respectively. In terms of the phase structure, oxidation treatment had little effect on the SiC fiber, while greatly influencing the SiC matrix. A weak peak corresponding to silica (SiO 2 ) appeared after high–temperature treatment of the fiber; however, oxidation treatment of the matrix led to the appearance of a very strong diffraction peak that corresponds to SiO 2 . The analysis of the morphology and composition indicated cracking of the fiber surface after oxidation treatment, which was increasingly obvious with the increase in the oxidation treatment temperature. The elemental composition of the fiber surface changed significantly, with drastically decreased carbon element content and sharply increased oxygen element content.

Effect of pyrolysis temperatures on the performance of SiCf/SiC composites

Continuous silicon carbide fiber reinforced silicon carbide matrix composites (SiCf/SiC) are promising candidate materials for nuclear applications. In this paper, three–dimensional (3D) SiCf/SiC composites were fabricated using the polymer infiltration and pyrolysis (PIP) process at different pyrolysis temperatures (i.e. 1100, 1300 and 1500°C). The effect of the pyrolysis temperature on the thermal and mechanical properties of the SiCf/SiC composites was investigated with a laser flash method, a three–point bending test and a single–edged notch beam method. The results indicated that the thermal diffusivity of the SiCf/SiC composites improved considerably with increasing pyrolysis temperatures, due to a higher degree of crystallization in the matrix. Additionally, as the testing temperature increased, the thermal diffusivity of the SiCf/SiC composites gradually decreased. With increasing pyrolysis temperatures, the mechanical properties of the SiCf/SiC composites first increased and later decreased. The SiCf/SiC composites fabricated at 1300°C had the highest average flexural strength and fracture toughness, i.e. 535.6MPa and 17.3MPam1/2, respectively.

Feasibility of Electrochemical Deposition of Nickel/Silicon Carbide Fibers Composites over Nickel Superalloys

Nickel superalloys are typical materials used for the hot parts of engines in aircraft and space vehicles. They are very important in this field as they offer high-temperature mechanical strength together with a good resistance to oxidation and corrosion. Due to high-temperature buckling phenomena, reinforcement of the nickel superalloy might be needed to increase stiffness. For this reason, it was thought to investigate the possibility of producing composite materials that might improve properties of the metal at high temperature. The composite material was produced by using electrochemical deposition method in which a composite with nickel matrix and long silicon carbide fibers was deposited over the nickel superalloy. The substrate was Inconel 718, and monofilament continuous silicon carbide fibers were chosen as reinforcement. Chemical compatibility was studied between Inconel 718 and the reinforcing fibers, with fibers both in an uncoated condition, and coated with carbon or carbon/titanium diboride. Both theoretical calculations and experiments were conducted, which suggested the use of a carbon coating over the fibers and a buffer layer of nickel to avoid unwanted reactions between the substrate and silicon carbide. Deposition was then performed, and this demonstrated the practical feasibility of the process. Yield strength was measured to detect the onset of interface debonding between the substrate and the composite layer.