SiC Fiber-reinforced Composites Research Articles

Fabrication of carbon fiber reinforced SiC composites based on laser directed energy deposition

Carbon fiber reinforced silicon carbide ceramic matrix composites (CF/SiC) are widely applied in aerospace and other industries fields for its extraordinary properties. Nevertheless, traditional preparation processes encounter the challenges of long cyclicality, high economic cost due to the increasing requests. Consequently, this work integrates the CF/SiC composites with the novel laser directed energy deposition (L-DED) printing technology, which is differing from conventional 3D printing technology for it omits the post-processing procedure. CF/SiC composites are designed and manufactured efficiently, and the effects of carbon fiber addition are analyzed. Mechanical properties are utilized to characterize the internal bonding strength and the results reveal that the maximum flexural and compressive reach 119.33 ± 4.04 MPa and 396.20 ± 10.21 MPa, respectively, attributed to the enhanced crack propagation resistance caused by the carbon fiber addition. At the same time, this paper not only characterizes the performance through objective experimental data, but also expounds the formation mechanism of pores and cracks through material analysis. In conclusion, this work pioneers the application of L-DED molding technology to CF/SiC composites fabrication and validated its preparation capability, which not only improves the efficiency but also opens up a new path for CF/SiC composites preparation in the field of 3D printing.

Fabrication of bamboo-inspired continuous carbon fiber-reinforced SiC composites via dual-material thermally assisted extrusion-based 3D printing

Ceramic matrix composites (CMCs) structural components encounter the dual challenges of severe mechanical conditions and complex electromagnetic environments due to the increasing demand for stealth technology in aerospace field. To address various functional requirements, this study integrates a biomimetic strategy inspired by gradient bamboo vascular bundles with a novel dual-material 3D printing approach. Three distinct bamboo-inspired structural configurations Cf/SiC composites are designed and manufactured, and the effects of these different structural configurations on the CVI process are analyzed. Nanoindentation method is utilized to characterize the relationship between interface bonding strength and mechanical properties. The results reveal that the maximum flexural strength and fracture toughness reach 108.6 ± 5.2 MPa and 16.45±1.52 MPa m1/2, respectively, attributed to the enhanced crack propagation resistance and path caused by the weak fiber-matrix interface. Furthermore, the bio-inspired configuration enhances the dielectric loss and conductivity loss, exhibiting a minimum reflection loss of −24.3 dB with the effective absorption band of 3.89 GHz. This work introduces an innovative biomimetic strategy and 3D printing method for continuous fiber-reinforced ceramic composites, expanding the application of 3D printing technology in the field of CMCs.

Thermally assisted extrusion-based 3D printing of continuous carbon fiber-reinforced SiC composites

A novel method for the three-dimensional (3D) printing of continuous carbon fiber-reinforced SiC composites is proposed. A thermally assisted extrusion-based 3D printing system was developed to simultaneously print a thermoplastic SiC ink, which exhibited shear-thinning properties at high temperatures and underwent rapid solidification at room temperature, and continuous carbon fiber bundles. The viscosity, thixotropy, and printability of the thermoplastic ink were optimized by varying the content of SiC whiskers. Furthermore, the established correlation between the ink composition, nozzle structure, and printability demonstrated that fiber deviations in filaments could be minimized by selecting an appropriate whisker content and coaxial nozzle. A trade-off between the dimensional accuracy and mechanical properties of the printed materials was achieved by optimizing the ink composition and nozzle structure. Finally, PIP was combined for composite densification; the final specimens exhibited a maximum bending strength of 149.1 ± 8 MPa and fracture toughness of 5.32 ± 0.4 MPa·m1/2.

Microstructure and Mechanical Properties of Unidirectional, Laminated Cf/SiC Composites with α-Al2O3 Nanoparticles as Filler.

The effects of an α-Al2O3 nanoparticle filler in the SiC matrix on the mechanical properties and failure mechanism of the unidirectional, laminated carbon fiber-reinforced SiC composites were investigated in this work. First, α-Al2O3 nanoparticles were added to the carbon fiber bundles using a slurry impregnation method, and then the Cf/SiC composite with an α-Al2O3 nanoparticle filler (Cf/SiC-Al2O3) was fabricated using a precursor infiltration and pyrolysis method. The microstructure of the Cf/SiC-Al2O3 composite showed chemical compatibility between the α-Al2O3 and the pyrolysis SiC. The Cf/SiC-Al2O3 composite with a low porosity of ~6.67% achieved a good flexural strength of 629.3 MPa and a good fracture toughness of 25.2 MPa·m1/2. The interlaminar shear strength of the Cf/SiC-Al2O3 composite was 11.7 MPa. The SiC-Al2O3 matrix also presented a considerable Young’s modulus of 138.2 ± 8.66 GPa and hardness of 10.3 ± 1.03 GPa. Further analysis indicated that the good mechanical properties with the addition of an α-Al2O3 filler were not only related to the dense matrix and the improvement of the mechanical properties of the matrix. They also originated from the thermal residual compressive stress in the SiC matrix close to the α-Al2O3 nanoparticles caused by the thermal expansion mismatch, which could reflect and close the cracks in the matrix. The findings of this study provide more methods for designing new composites exhibiting a good performance.

Effects of interfacial residual stress on mechanical behavior of SiCf/SiC composites

Layer-structured interphase, existing between reinforcing fiber and ceramics matrix, is an indispensable constituent for fiber-reinforced ceramic composites due to its determinant role in the mechanical behavior of the composites. However, the interphase may suffer high residual stress because of the mismatch of thermal expansion coefficients in the constituents, and this can exert significant influence on the mechanical behavior of the composites. Here, the residual stress in the boron nitride (BN) interphase of continuous SiC fiber-reinforced SiC composites was measured using a micro-Raman spectrometer. The effects of the residual stress on the mechanical behavior of the composites were investigated by correlating the residual stress with the mechanical properties of the composites. The results indicate that the residual stress increases from 26.5 to 82.6 MPa in tension as the fabrication temperature of the composites rises from 1500 to 1650 °C. Moreover, the increasing tensile residual stress leads to significant variation of tensile strain, tensile strength, and fiber/matrix debonding mode of the composites. The sublayer slipping of the interphase caused by the residual stress should be responsible for the transformation of the mechanical behavior. This work can offer important guidance for residual stress adjustment in fiber-reinforced ceramic composites.

Long-term oxidation behavior of C/SiC-SiBCN composites in wet oxygen environment

Polymer derived SiBCN ceramic was introduced into carbon fiber reinforced SiC composites to prepare C/SiC-SiBCN composites. Weight change and flexural strength of the samples after oxidation at different temperatures and in different atmospheres were tested up to 100 h to investigate their wet oxidation behavior. It was found that the stable silicoboron glassy self-healing phase formed from the oxidation of SiBCN had favorable oxidation resistance in wet oxygen atmosphere. And the SiC-SiBCN matrix can provide about 50 h of protection for carbon fiber in wet oxygen. Besides, the influence of temperature on the oxidation behavior of C/SiC-SiBCN composites were much related to the release speed of gas products (B2O3, HBO2 and Si(OH)4). And the oxidation mechanism of SiC/SiC-SiBCN composites were further explained by the comparation with C/SiC-SiBCN composites.

Effects of initial density during laser machining assisted CVI process and its influence on strength of C/SiC composites

Novel laser-assisted chemical vapor infiltration (LA-CVI) technique has been used to improve the density and strength of carbon fiber reinforced SiC composites (C/SiC). Initial density of C/SiC before laser machining played an important role in determining the final density and strength of composites. Results show that final density and bending strength of lower initial density composites were better than that of higher initial density samples after LA-CVI process, while the porosity exhibited opposite behavior. Micro-CT and COMSEL simulation results verify that after LA-CVI process, dense band width of C/SiC with initial density of 1.5 g/cm3 was twice as that of C/SiC with initial density of 1.8 g/cm3. This led to crack propagation bypassing the micro-hole. In conclusion, low initial density when laser machining was carried out resulted in better properties of final composites.

Enhancement of the microwave absorption properties of PyC-SiCf/SiC composites by electrophoretic deposition of SiC nanowires on SiC fibers

The employment of coating technique on the silicon carbide fibers plays a pivotal role in preparing SiC fiber-reinforced SiC composites (SiCf/SiC) toward electromagnetic wave absorption applications. In this work, SiC nanowires (SiCNWs) are successfully deposited onto the pyrolytic carbon (PyC) coated SiC fibers by an electrophoretic deposition method, and subsequently densified by chemical vapor infiltration to obtain SiCNWs/PyC-SiCf/SiC composites. The results reveal that the introduction of SiCNWs could markedly enhance the microwave absorption properties of PyC-SiCf/SiC composites. Owing to the increasing of SiCNWs loading, the minimum reflection loss of composites raises up to −58.5 dB in the SiCNWs/PyC-SiCf/SiC composites with an effective absorption bandwidth (reflection loss ≤ −10 dB) of 6.13 GHz. The remarkable enhancement of electromagnetic wave absorption performances is mainly attributed to the improved dielectric loss ability, impedance matching and multiple reflections. This work provides a novel strategy in preparing SiCf/SiC composites with excellent electromagnetic wave absorption properties.

Microstructure and oxidation behavior of a novel bilayer (c-AlPO4–SiCw–mullite)/SiC coating for carbon fiber reinforced CMCs

A novel cristobalite aluminum phosphate particle (c-AlPO4) modified SiC whisker toughened mullite coating (c-AlPO4-SiCw-mullite) was prepared on SiC coated carbon fiber reinforced SiC composites (C/SiC) by a new sol-gel method combined with air spraying to improve the oxidation resistance of SiCw-mullite coating. Results show that c-AlPO4-SiCw-mullite coatings with 10 and 20 wt.% of c-AlPO4 exhibited obviously improved oxidation resistance at 1773 K in ambient air for 100 h than SiCw-mullite coating. Moreover, the oxidation resistance of c-AlPO4-SiCw-mullite coatings were rapidly declined when the c-AlPO4 in c-AlPO4-SiCw-mullite coating were set to 30 and 40 wt.%. The c-AlPO4-SiCw-mullite coating with 20 wt.% of c-AlPO4 showed most pronounced oxidation resistance, the weight loss rate after the oxidation in ambient air for 210 h was merely 3.00 × 10−5 g·cm−2 h−1. The failure of c-AlPO4-SiCw-mullite coating with 20 wt.% of c-AlPO4 was due to the generation of penetrative micro-cracks and micro-holes in the coating, which cannot be self-healed by the silicate glass layer after long time oxidation at 1773 K.

Fabrication and mechanical behavior of ZrB2 strengthened SiCf/SiC composites prepared by hybrid processing route

A SiC fiber-reinforced composite containing a SiC-ZrB2 mixed matrix (SiCf/(SiC-ZrB2)) with high density and enhanced mechanical properties was fabricated. ZrB2 at 5 or 40 vol% was added to a (SiC + C) slurry to be infiltrated into the voids of 2D woven Tyranno™-SA grade-3 fabrics by electrophoretic deposition. Subsequent hot pressing at 1300 °C and 10 MPa for 1 h, followed by liquid silicon infiltration (LSI) at 1600 °C for 5 h in an Ar atmosphere resulted in the formation of the reaction-bonded SiC matrix, which revealed a composite density close to 97%. SiCf/(SiC-ZrB2) having open porosities of 0.2–0.6% showed peak strengths of 398 and 320 MPa for 5 and 40 vol% ZrB2 addition, respectively. The large mismatch in the coefficient of thermal expansion and Young's modulus between the SiC and ZrB2 phases was attributed to a reverse trend in the strength of composites. Brittle behavior of the composites in flexure can be explained by the strong bonding between the matrix and fibers formed by the reaction of interphase with molten Si during LSI. Strength retention after oxidation at 1000 and 1400 °C for 2 h was also compared in terms of ZrB2 amount contained in the composites.

Effect of fiber heat treatment on microstructure and mechanical properties of 2.5D T700 carbon fiber reinforced SiC composites

T700 carbon fibers were heat treated at 1300 °C and 1600 °C to investigate the effect on microstructure of pyrolytic carbon (PyC) interphase and mechanical properties of 2.5D T700 carbon fiber reinforced SiC (2.5D Cf/SiC) composites, and the untreated carbon fiber acts as a comparison. The flexural strength was measured using three-point bending test and the fracture toughness was evaluated by a single-edge notched beam test. Results show that heat treatment at 1300 °C leads to highest mechanical properties of 2.5D Cf/SiC composites, with the flexural strength in warp direction of 248.6 ± 12.3 MPa, the flexural strength in weft direction of 421.6 ± 15.1 MPa, and the fracture toughness of 18.7 ± 1.7 MPa · m1/2. Nevertheless, both the unheated and heat treatment at 1600 °C result in a decrease in mechanical properties. The microstructural investigations revealed that the bonding strength between the carbon fiber and PyC is best when the heat treatment of carbon fiber at 1300 °C.

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.

Enhancing the fracture resistance of carbon fiber reinforced SiC matrix composites by interface modification through a simple fiber heat-treatment process

A simple method to significantly increase the toughness of carbon fiber reinforced SiC matrix composites is presented. The method is based on the heat treatment of Toray T300 carbon fibers in vacuum, leading to the in-situ formation of carbon coatings on the fiber surface that optimizes the interfacial strength in carbon fiber reinforced SiC matrix composite. The formation mechanism of the in-situ coatings was studied by transmission electron microscopy, and the effects of the in-situ carbon interphase on the interfacial property and fracture resistance of the composites were comprehensively assessed by combining transmission electron microscopy, fiber push-in and macro mechanical testing. The results reveal that the in-situ coating was originated from the pyrolysis of the proprietary sizing of the T300 fibers, that was crystallized during thermal treatment, maintaining a low oxygen content. For this reason, the resulting coating can effectively hinder the interfacial reactions in carbon fiber reinforced SiC composites, and remarkably weaken the composite interfacial shear strength from 105 ± 10 MPa to 30 ± 5 MPa. Due to the introduction of in-situ carbon interphase, the toughness of the carbon fiber reinforced SiC composite increased significantly from 1.7 ± 0.3 MPa m1/2 to 21.3 ± 0.7 MPa m1/2, triggered by toughening mechanisms such as crack deflection and fiber pullout.

Fabrication of Mullite Coating and its Oxidation Protection for Carbon Fiber Reinforced SiC Composites

To protect carbon fiber-reinforced SiC (C/SiC) composites against oxidation,mullite coating was prepared on C/SiC composites by dip-coating method with high solid content Al2O3-SiO2 sol as raw materials. X-ray diffraction and scanning electron microscopy were employed to analyze the phase and microstructure of the coating. The results show that the as-prepared coating is SiO2-rich, monolithic and well bonded with substrate without penetrating crack, giving rise to good oxidation-resistance. After soaked at 1400°C for 30min under static air, the coated C/SiC composites possess 87% of original flexural strength. As a result of sealing and filling of cracks and pores by viscous SiO2 in coating, the coated C/SiC composites exhibit improved oxidation resistance at 1500°C and 1600°C. There is no change in flexural strength after oxidized at 1500°C and 1600°C for 30min, respectively. Nevertheless, the carbothermal reduction between viscous SiO2 and free carbon in C/SiC substrate would occur obviously when oxidation temperature was elevated or oxidation time was prolonged, leading to local foaming in coating and decreasing in oxidation resistance.

Quasi-static and dynamic compressive fracture behavior of SiCf/SiC composites

To understand the quasi-static and dynamic compressive mechanical behavior of two-dimensional SiC fiber-reinforced SiC composites (2D-SiCf/SiC), their compressive behavior at room temperature was investigated at a strain rate from 10−4 to 104 /s, and the fracture surfaces and damage morphology were observed. The results show that the dynamic failure strength of 2D-SiCf/SiC obeys the Weibull distribution, and the Weibull modulus is 5.66. Meanwhile, 2D-SiCf/SiC presents a transition from brittle to tough with a decrease of strain rate, and 2D-SiCf/SiC has a more significant strain rate sensitivity compared to the 2D-C/SiC composites. The failure mode of 2D-SiCf/SiC depends upon the strain rate.

Complete recovery of high temperature oxidation resistance in carbon fiber reinforced SiC composites by a recoating repair methodology

The current work reports on the oxidation behavior and residual flexural strength of carbon fiber–reinforced silicon carbide composites (C/SiC) after induction of thermal crack damage by heat treatment (HT) at 1900°C and the effect, therein, of a repair process involving recoating by SiC. As-prepared, heat-treated and heat-treated/recoated specimens, were subjected to static oxidation tests in air at a temperature range of 500–1500°C for 10h and then tested in three-point bending. It was found that composite weight of heat-treated samples decreased dramatically with increasing oxidation temperature with weight loss values of ~30% being systematically observed for oxidation temperatures above 800°C. On the other hand, as-prepared and heat-treated/SiC-recoated specimens reached almost their original weight after oxidation. The residual flexural strength of C/SiC composites with thermally-induced crack damage decreased significantly compared to as-prepared specimens, while SiC recoating was found to efficiently enable strength enhancement. Microstructural analysis showed that HT was associated with increased population and dimensions of micro-cracks on the C/SiC surface while SiC recoating enabled repair of HT-induced thermal crack damage hence leading to oxidation resistance recovery of the material.

Fabrication of SiCf/SiC composites by alternating current electrophoretic deposition (AC–EPD) and hot pressing

Abstract Alternating current electrophoretic deposition (AC–EPD) was used to infiltrate a SiC-based matrix phase containing Al 2 O 3 –Sc 2 O 3 sintering aids into the fine voids of a two-dimensionally woven Tyranno™-SA3 SiC fabric preform for the fabrication of a dense SiC fiber-reinforced SiC composite (SiC f /SiC). The zeta potential of the aqueous suspension was set to ≥−55 mV to achieve uniform and simultaneous deposition of all constituent particles. EPD was performed at 20 V AC for 30 min under the application of ultrasonic pulses for the initial 20 min to minimize the surface sealing effect. A high SiC f /SiC density of 96.5% along with a flexural strength of 413.9 ± 18.5 MPa was achieved after hot pressing at 1750 °C for 1 h due to the high degree of matrix phase infiltration. These results showed that an eco-friend AC–EPD process can be applied to the fabrication of high density SiC f /SiC.

Fabrication of Dense Carbon Fiber Reinforced SiC Composites by Controlling the Rheology of Polycarbosilane Solution

Fabrication of Dense Carbon Fiber Reinforced SiC Composites by Controlling the Rheology of Polycarbosilane Solution

Fabricating hollow turbine blades using short carbon fiber-reinforced SiC composite

The development of hollow turbine blades fabricated by nickel-base superalloy is limited by its high density and low operating temperature (<1,100 °C). A new technology for fabricating hollow turbine blades of fiber-reinforced SiC composite was put forward. The chemical corrosion process of DSM Somos 19120 resin mold was investigated, and the pyrolysis of phenolic resin and the infiltration of liquid silicon were analyzed by using scanning electron microscope and X-ray diffraction. The influence of carbon fiber content on fracture strength and fracture toughness of fiber-reinforced SiC composite was investigated using the measurement of three-point flexural strength test. Results showed that stereolithography molds of photosensitive resin were corroded perfectly using KOH alcohol water solution. The porous carbon preforms were obtained after phenolic resin was pyrolyzed from 400 to 800 °C, which were then infiltrated with molten silicon to gain SiC matrix at the temperature of 1,450 °C in 1 h. The fracture strength and fracture toughness of SiC ceramic matrix were enhanced with the increase of short carbon fiber content. The maximum fracture strength and fracture toughness of samples were about 270 MPa and 5.1 MPa m1/2, respectively. Finally, hollow turbine blades were successfully fabricated using short carbon fiber-reinforced SiC composite.

Mechanical and Tribological Properties of 3D Carbon Fiber Reinforced SiC Composites Prepared by Liquid Silicon Infiltration

C/SiC composites were prepared by liquid silicon infiltration process, and their microstructure, mechanical and tribological properties were studied in this paper. The results showed that the composites demonstrated non-catastrophic fracture behavior with long fibers pulled out and about 115 MPa flexural strength. The stability of coefficient of friction (COF) was improved and wear rate demonstrated a linear variation with the increasing of rotation speeds. However, wear rate exhibited a higher value (~3.6 μg/m) under a higher load (~150 N), even though the COF curves for C/SiC composites showed no significant changes.