Fabrication and mechanical properties of carbon fibers/lithium aluminosilicate ceramic matrix composites reinforced by in-situ growth SiC nanowires

To improve the mechanical properties of carbon fibers/lithium aluminosilicate (C_f/LAS) composites, C_f/LAS with in-situ grown SiC nanowires (SiC_nw-C_f/LAS) were prepared by chemical vapor phase reaction, precursor impregnation, and hot press sintering, consecutively. The effect of multi-scaled reinforcements (micro-scaled C_f and nano-scaled SiC_nw) on the mechanical properties was investigated. The phase composition, microstructure and fracture surface of the composites were characterized by XRD, Raman Spectrum, SEM, and TEM. The morphology of SiC_nw has a close relation with the content of Si. Microstructure analysis suggests that the growth of SiC nanowires depends on the VLS mechanism. The multi-scale reinforcement formed by C_f and SiC_nw can significantly improve the mechanical properties of C_f/LAS. The bending strength of SiC_nw-C_f/LAS reaches to 597 MPa, achieving an increase of 19% to C_f/LAS. Moreover, the samples show a maximum fracture toughness of 11.01 MPa m^1/2, achieving an increase of 46.4% to C_f/LAS. Through analysis of the fracture surface, the improved mechanical properties could be attributed to the multi-scaled reinforcements by the pull-out and debonding of C_f and SiC_nw from the composites.     

Co-enhancement of oxidation resistance and mechanical properties of Cf/LAS composites: The effects of h-BN addition

Carbon fiber reinforced lithium aluminosilicate glass-ceramic composites have been extensively studied and widely used in industry applications, because of its good mechanical properties and low thermal expansion coefficient. However, further investigation is also need to improve its oxidation resistance and mechanical performance to meet higher requirements. In this work, C_f/LAS glass-ceramic composites were fabricated by a slurry impregnation and hot-pressing method with different amounts of h-BN. Results indicate that composites with 2 wt.% h-BN addition exhibit excellent flexural strength and fracture toughness, reaching 910 ± 22 MPa and 21 ± 1 MPa·m^1/2, respectively, and that after oxidation at 600, 800 and 1000 °C for 1 h, their strength residual ratio can reach 47%, 35% and 32%, respectively. TEM analyses suggest the improvement of oxidation resistance and mechanical properties should be attributed to the unique interface of composites caused by h-BN addition.     

ZrO2f-coated Cf hybrid fibrous reinforcements and properties of their reinforced ceramicizable phenolic resin matrix composites

Carbon fiber-reinforced ceramicizable phenolic resin matrix composites have been widely used in the field of thermal protection materials. In this paper, the ZrO_2f-coated C_f (ZrO_2f/C_f) hybrid fibrous reinforcements were designed to improve oxidation resistance of carbon fiber and ceramicizable composites reinforced by ZrO_2f/C_f hybrid fibrous reinforcements were prepared to investigated oxidation resistance and mechanical properties of the composites at high temperature. The results show that ZrO_2f/C_f hybrid fibrous reinforcements have good thermal stability and high oxidation resistance, and its ceramicizable composites have good bending strength at high temperature. Weight loss rate of the composites is only 21 %, and bending strength can be as high as 39 MPa when ablation time was 12 min at 1400 °C.     

Enhanced mechanical properties in Cf/LAS composite with yolk-shell structure interface

A new approach to improve the interfacial matching of carbon fiber-reinforced lithium-aluminum-silicon(C_f/LAS) composites is proposed, which is achieved by Ni nanoparticles catalyzing the formation of a tunable graphite layer on the surface of C_f. The interfacial structure between the composites can be effectively improved by tuning parameters such as Ni²⁺ content and sintering holding time, and ultimately, the mechanical properties of the composites can be improved. Interestingly, due to the introduction of Ni²⁺, a yolk-shell type graphite layer is formed between the C_f and LAS, and the bridging effect of the graphite layer improves interfacial bonding. The highest flexural strength (515 ± 30 MPa) and fracture toughness (14.7 ± 1.6 MPa·m^1/2) were obtained. Taking C_f/LAS as an example, the relationship between interfacial matching and mechanical properties of composites is systematically investigated and may provide a new idea for the improvement of mechanical properties of fiber-reinforced composites.     

A new route to fabricate SiB4 modified C/SiC composites

In order to improve the oxidation and thermal shock resistance of 2D C/SiC composites, dense SiB₄–SiC matrix was in situ formed in 2D C/SiC composites by a joint process of slurry infiltration and liquid silicon infiltration. The synthesis mechanism of SiB₄ was investigated by analyzing the reaction products of B₄C–Si system. Compared with the porous C/SiC composites, the density of C/SiC–SiB₄ composites increased from 1.63 to 2.23 g/cm³ and the flexural strength increased from 135 to 330 MPa. The thermal shock behaviors of C/SiC and C/SiC–SiB₄ composites protected with SiC coating were studied using the method of air quenching. C/SiC–SiB₄ composites displayed good resistance to thermal shock, and retained 95% of the original strength after being quenched in air from 1300 °C to room temperature for 60 cycles, which showed less weight loss than C/SiC composite.     

Microstructures and mechanical properties of Cf/LAS composite and Ti60 alloy joints brazed with TiZrNiCu + Cf mixed powders

In this paper, carbon fiber reinforced lithium aluminosilicate (LAS) glass-ceramics matrix composites (C_f/LAS composites) are joined to Ti60 alloy using TiZrNiCu + C_f mixed powders by proper process parameters. The carbon fibers distribute uniformly in the brazing interlayer and react with Ti, Zr elements in the brazing alloy to form (Ti, Zr)C thin reactive layers, which are between the carbon fibers and the Ti, Zr elements. The effect of C_f content on the mechanical properties and microstructure of brazed joints are investigated. The microstructure of brazed joints varied obviously with the increasing of C_f content. The thickness of reactive layer between interlayer and C_f/LAS composites and Ti solid solution (Ti (s.s)) decrease gradually, and the volume of eutectic structure (Ti(s,s) + (Ti,Zr)₂(Ni,Cu)) decrease gradually. The obtained brazed joints exhibit a maximum shear strength of 73.5 MPa at room temperature using TiZrNiCu + 0.3 wt% C_f mixed powders. The enhanced shear strength can be attributed to the reduction in thermal stress and the reinforcing effect originated from the carbon fiber addition.     

Two-step method to deposit ZrO2 coating on carbon fiber: Preparation,characterization, and performance in SiC composites

Recently, ceramic matrix composites reinforced by short carbon fibers (CFs) attracted increasing attentions. To further improve mechanical properties and oxidation resistances, CFs were subjected to oxidation and acidification followed by sol-gel dip-coating to deposit ZrO₂ on their surfaces. ZrO₂-C_f/SiC composites were fabricated by joint hot compression molding and sintering, compared to C_f/SiC and SiC prepared by the same method. Microstructural analyses indicated that ZrO₂ coatings were successfully deposited on CF surfaces, formed strong bonding and interfaces between CF and the matrix. Meanwhile, CFs were found uniformly distributed in SiC matrix with random orientations. Flexural curves of ZrO₂-C_f/SiC and C_f/SiC revealed the presence of “false plasticity” regions after sharp drops, which were quite different from brittle flexural behavior of SiC ceramic. Compression strength of the three samples showed step-up growth. ZrO₂-C_f/SiC exhibited the highest value, indicating the introduction of CFs and ZrO₂ coatings do have great influence on mechanical performances. After heat treatment, ZrO₂-C_f/SiC exhibited better oxidation resistance than C_f/SiC, with weight loss ratios estimated to ??3.76% and ??6.43%, respectively. These improved properties indicated that ZrO₂-C_f/SiC would be excellent alternatives to other existence materials under ultra-high temperature environments.     

Effect of preform and carbon matrix on bending strength of Cf/Cu/C composites

Aiming to obtain composites with appropriate mechanical properties for pantograph sliders, copper mesh modified carbon/carbon (C_f/Cu/C) composites were prepared by chemical vapor infiltration (CVI) in C₃H₆ +?N₂ atmosphere and impregnation-carbonization (I-C) with furan resin. In this paper, C_f/Cu/C composites with two kinds of preforms and carbon matrixes were obtained. The effect of preforms and carbon matrixes on bending strength was investigated. The results indicated that the bending strength of carbon fiber/copper mesh reinforced pyrolytic carbon matrix composites was about 181.39–195.43?MPa, while that reinforced resin carbon matrix composites had the worst bending strength around 54.45–57.04?MPa, in terms of the same preform. The bending strength of C_f/Cu/C composites in the parallel orientation and vertical orientation were also similar. As for C_f/Cu/C composites with the same carbon matrix, the bending strength of C_f/Cu/C composites with non-woven fiber/fiber web/copper mesh type preform was higher than that with fiber web/copper mesh type preform. However, the bending strength of carbon fiber/copper mesh reinforced resin carbon matrix composites showed the opposite trend, and its reasons were analyzed and discussed taking advantage of the fracture mechanisms.     

Degradation behavior of SiO2f/Al2O3-SiO2 composites: Anti-oxidation behavior and high-temperature flexural strength

2.5-Dimensional SiO₂ fiber-reinforced Al₂O₃-SiO₂ (SiO_2f/Al₂O₃-SiO₂) composites were prepared by the sol-gel method, using diphasic SiO₂ sol as the precursor into which Al₂O₃ powders were added. Their antioxidative behaviors and flexural strengths at high temperature were tested and compared. In an oxidation atmosphere, the composites showed high oxidation resistance, with a flexural strength retention ratio of over 90.00% at 1200?°C. After oxidation at 1500?°C, the mass retention ratio and flexural strength were 97.49% and 65.0?MPa respectively. The oxidation resistance of SiO_2f/Al₂O₃-SiO₂ composites was higher than that of SiO_2f/SiO₂ composites. After high-temperature test, the flexural strength retention ratios of SiO_2f/SiO₂ and SiO_2f/Al₂O₃-SiO₂ composites were 86.18% and 94.80% respectively, and the latter had a flexural strength of 134.9?MPa. SiO_2?f/Al₂O₃-SiO₂ composites worked better than SiO_2f/SiO₂ composites did in the flexural strength test at 1200?°C. The mechanical performance degradation and mass variations of the composites during tests were closely associated with their microstructural evolutions.     

Fabrication of carbon fiber reinforced ceramic matrix composites with improved oxidation resistance using boron as active filler

Boron was introduced into C_f/SiC composites as active filler to shorten the processing time of PIP process and improve the oxidation resistance of composites. When heat-treated at 1800 °C in N₂ for 1 h, the density of composites with boron (C_f/SiC-BN) increased from 1.71 to 1.78 g/cm³, while that of composites without boron (C_f/SiC) decreased from 1.92 to 1.77 g/cm³. So when boron was used, two cycles of polymer impregnation and pyrolysis (PIP) could be reduced. Meanwhile, the oxidation resistance of composites was greatly improved with the incorporation of boron-bearing species. Most carbon fiber reinforcements in C_f/SiC composite were burnt off when they were oxidized at 800 °C for 10 h. By contrast, only a small amount of carbon fibers in C_f/SiC-BN composite were burnt off. Weight losses for C_f/SiC composite and C_f/SiC-BN composite were about 36 and 16 wt%, respectively.     

Ablation resistance of HfC(Si,O)-HfB2(Si,O) composites fabricated by one-step reactive spark plasma sintering

A dense HfC(Si, O)-HfB₂(Si, O) composite was fabricated by reactive spark plasma sintering using HfC and SiB₆ as starting reactants. The best ablation resistance was obtained with the composite fabricated with the addition of 15 vol.% SiB₆. After ablation under an oxyacetylene flame for 60 s, the mass and linear ablation rates of this composite were ?0.007 mg cm^?2 s^?1 and ?0.233 μm s^?1, respectively. The negative ablation rates are the result of a slight mass gain/thickness increase, which indicate that the oxidation process was stable and mechanical scouring was limited during ablation. This enhanced ablation resistance was attributed to a unique double-layered oxide formation, which possessed lower oxygen permeability and better mechanical strength. The solid solution nature of the composite and its appropriate phase composition were responsible for the stable oxide structure formation.     

TaSi2–SiC high-emissivity coating modified by SiB6 on flexible alumina fibre fabric with enhanced oxidation resistance and high interfacial bonding strength

To improve the oxidation inhibition of TaSi₂-based high-emissivity coatings at high temperatures, TaSi₂–SiC coating modified by SiB₆ was prepared on the surface of alumina fibre fabrics. The effects of the SiB₆ content on the surface appearance and emissivity of the coating were investigated, and the mechanical properties of the coated fabrics were compared. When the SiB₆ content in the coating was 2.5%, the borosilicate glass liquid phase generated by SiB₆ oxidation effectively prevented the oxidation of TaSi₂. The bond strength between the coatings and fibre fabric was 207 kPa after calcination at 1200 °C, which was 39% higher than that of the coated fabric without SiB₆. The emissivity of the TaSi₂–SiC coating, modified by a SiB₆ content of 2.5%, reached above 0.92 after calcination at 1200 °C for 5 h. Therefore, the TaSi₂–SiC high-emissivity coating modified by SiB₆ has good application prospects in the field of thermal protection.     

Fabrication process and growth mechanism of novel micro-stack PyC interphase with different textures

Pyrolytic carbon (PyC) interphase plays a crucial role in the mechanical properties of fiber-reinforced ceramic matrix composites. In this research, a novel micro-stack PyC interphase with different PyC textures was designed and fabricated by changing the deposition parameters during the chemical vapor infiltration process. The growth mechanism of the micro-stack PyC interphase with different texture were also studied by experimental characterizations and kinetic calculations, and the results show that the content ratio of (C₂H₂ + C₂H₄) to C₆H₆ gas intermediate is a key parameter to control the texture types of PyC interphase. Furthermore, the value of orientation angle (OA) value, thickness, and modulus of the micro-stack PyC interphase were further characterized by high resolution TEM (HRTEM), scanning electronic microscopy, and nanoindentation. Finally, the tensile testing of mini-C_f/PyC/SiC composites was conducted, and the results showed that the tensile strength of mini-C_f/PyC/SiC composites with micro-stack PyC interphase is approximately 40% higher than that containing single high texture PyC interphase. The improvements on the tensile strength of C_f/PyC/SiC composites prove the significant advantages of micro-stack PyC interphase.     

Processing and properties of Cfibre/SiCfillers/SiOC composites using solvent free liquid polysiloxane as matrix source

Abstract

Carbon fibre reinforced SiOC composites (denoted as C_fibre/SiC_fillers/SiOC) were prepared by slurry coating and polymer infiltration pyrolysis (PIP) process. Low viscosity liquid polysiloxane (PSO) and SiC powder were combined at a 1∶1 weight ratio to produce a blend (S-PSO), which was employed as matrix source. Heat treated carbon fibre fabric was adopted as the reinforcement. The lamination process was determined on the basis of cure and rheology investigations on S-PSO. The effects of PIP cycles and temperature of heat treatment of the carbon fibre on the mechanical properties of C_fibre/SiC_fillers/SiOC were examined. The results indicate that composites using carbon fibres annealed at 1700°C as reinforcement reached a maximum flexural strength of 300 MPa after six PIP cycles. The resistance of the C_fibre/SiC_fillers/SiOC composite to oxidation was also evaluated. Without any protective coatings, the composite retained 60% of its strength after oxidation at 800°C for 3 h in a static air environment.     

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

Continuous silicon carbide fiber reinforced silicon carbide matrix (SiC_f/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 SiC_f/SiC composites, the crystallization rate and initial damage degree of SiC fibers are seriously influenced by preparation temperatures of SiC_f/SiC composites, namely mechanical properties of SiC fibers and SiC_f/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 SiC_f/SiC composites. In addition, finite element method (FEM) based on representative volume element (RVE) was adopted to predict the mechanical properties of SiC_f/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 SiC_f/SiC composites while transverse shear properties were not significantly various. And the mechanical properties of SiC_f/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 SiC_f/SiC composites.     

Ablation properties and mechanisms of BN-coated Cf-reinforced SiBCNZr ceramic composites under an oxyacetylene combustion torch

The ablation properties andmechanisms of BN-coated C_f-reinforced SiBCNZr composites under an oxyacetylene combustion torch were investigated. The mass and linear ablation rates of the C_f/SiBCNZr ceramic matrix composites were lower than those of C_f/SiBCN and SiC_f/SiBCN composites, reaching 0.0022 mg/s and 0.0136 mm/s, respectively. The ablation resistance of the SiBCN ceramics was enhanced by the addition of Zr, whereas the BN-coated C_f increased the thermal shock resistance of the SiBCNZr ceramics. No macrocracks were found on the ablation surface of the C_f/SiBCNZr specimen. The ablation mechanisms based on different ablation temperatures, phase evolution during ablation, and ablation morphologies in the different ablation regions consisted of oxidation of the carbon fibre and ceramic matrix, emission of various gases, the flow of high-viscosity SiO₂, and denudation of C_f under the erosion of the ablation flame.     

Polymer derived ceramic materials from Si,B and MoSiB filler-loaded perhydropolysilazane precursor for oxidation protection

Silica-based coating systems were developed using polymer derived ceramics (PDCs) technology. Ceramic composites on the base of a SiO₂ and SiNO matrix and homogeneously distributed Mo₅SiB₂, SiB₆, Si and B fillers were manufactured. The coating systems have low porosity and provide a high oxidation resistance up to 100 h at 800 °C and 1100 °C in air. The influence of temperature and atmosphere of pyrolysis on the polymer precursor, the volume fraction of filler materials on the chemical composition of compacts as well as their high-temperature oxidation protection was investigated.     

Improved mechanical properties of SiB6 reinforced silica-based ceramic cores fabricated by 3D stereolithography printing

Silica-based ceramic core is an extremely critical component in the manufacture of hollow blades during investment casting. However, the traditional preparation methods rely more on the molds, and the manufacturing costs are relatively high. In this study, silica-based ceramics with silicon hexaboride (SiB₆) addition were prepared via 3D stereolithography printing. And the effects of the SiB₆ content on mechanical properties of the obtained ceramic samples were explored. As the SiB₆ content increased to 2.0 wt%, the linear shrinkage gradually decreased, while the room temperature and high temperature flexural strength were enhanced at the SiB₆ content from 0 to 1.0 wt% and reduced as the SiB₆ content further rose. As the SiB₆ content increased to 1.0 wt%, the linear shrinkage was reduced to 1.86% resulting from the oxidation reaction of SiB₆. Furthermore, with 1.0 wt% SiB₆ addition, the flexural strength of the samples at room temperature was enhanced from 6.75 MPa to 14.63 MPa due to the sintering promotion of oxidation product B₂O₃, and the flexural strength at 1550 °C was improved from 7.68 MPa to 13.08 MPa because of the enhanced β-cristobalite content, which is suitable for high temperature casting of ceramic cores. Therefore, it demonstrates the capability of fabricating SiB₆ reinforced silica-based ceramic cores with high performance via stereolithography.     

Microstructure and mechanical properties of quasi-isotropic chopped fiber-reinforced PyC–SiC matrix composite prepared by novel nondamaging method

In this work, quasi-isotropic chopped carbon fiber-reinforced pyrolytic carbon and silicon carbide matrix (C_f/C–SiC) composites and chopped silicon carbide fiber-reinforced silicon carbide matrix (SiC_f/SiC) composites were prepared via novel nondamaging method, namely airlaid process combined with chemical vapor infiltration. Both composites exhibit random fiber distribution and homogeneous pore size. Young's modulus of highly textured pyrolytic carbon (PyC) matrix is 23.01 ± 1.43 GPa, and that of SiC matrix composed of columnar crystals is 305.8 ± 9.49 GPa in C_f/C–SiC composites. Tensile strength and interlaminar shear strength of C_f/C–SiC composites are 52.56 ± 4.81 and 98.16 ± 24.62 MPa, respectively, which are both higher than those of SiC_f/SiC composites because of appropriate interfacial shear strength and introduction of low-modulus and highly textured PyC matrix. Excellent mechanical properties of C_f/C–SiC composites, particularly regarding interlaminar shear strength, are due to their quasi-isotropic structure, interfacial debonding, interfacial sliding, and crack deflection. In addition to the occurrence of crack deflection at the fiber/matrix interface, crack deflection in C_f/C–SiC composites takes also place at the interface between PyC–SiC composite matrix and the interlamination of multilayered PyC matrix. Outstanding mechanical properties of as-prepared C_f/C–SiC composites render them potential candidates for application as thermal structure materials under complex stress conditions.     

Long-term oxidation and ablation behavior of Cf/ZrB2–SiC composites at 1500, 2000, and 2200°C

Although C_f/ZrB₂–SiC composites prepared via direct ink writing combined with low-temperature hot-pressing were shown to exhibit high relative density, high preparation efficiency, and excellent flexural strength and fracture toughness in our previous work, their oxidation and ablation resistance at high and ultrahigh temperatures had not been investigated. In this work, the oxidation and ablation resistance of C_f/ZrB₂–SiC composites were evaluated via static oxidation at high temperature (1500°C) and oxyacetylene ablation at ultrahigh temperatures (2080 and 2270°C), respectively. The thickness of the oxide layer of the C_f/ZrB₂–SiC composites is <40 μm after oxidizing at 1500°C for 1 h. The C_f/ZrB₂–SiC composites exhibit non-ablative properties after oxyacetylene ablation at 2080 and 2270°C for >600 s, with mass ablation rates of 3.77 × 10⁻³ and 5.53 × 10⁻³ mg/(cm² s), and linear ablation rates of −4.5 × 10⁻⁴ and −5.8 × 10⁻⁴ mm/s, respectively. Upon an increase in the ablation temperature from 2080 to 2270°C, the thickness of the total oxide layer increases from 360 to 570 μm, and the carbon fibers remain intact in the unaffected region. Moreover, the oxidation and ablation process of C_f/ZrB₂–SiC at various temperatures was analyzed and discussed.