SiC Fibers Research Articles

High‐efficiency electromagnetic absorption of HfC–SiCf ceramics with a 3D reticular structure

AbstractThe development of high‐temperature electromagnetic (EM) wave absorbing materials is an important direction for achieving radar stealth in high‐speed aircraft. In this study, HfC–SiCf composite ceramics with 3D reticular structure were synthesized in one‐step using the molten‐salt‐assisted carbon thermal reduction method. During the synthesis process, SiC grew in situ into a fibrous structure with a diameter of 500 nm and lengths ranging from 2 to 30 µm. By adjusting the molar ratio of HfC to SiC, the HfC‐30 mol% SiC (HS30) exhibited the best EM absorption performance at room temperature, with a minimum reflection loss (RLmin) of −31.4 dB at 16.1 GHz and an effective absorption bandwidth (EAB) of 4.6 GHz. The excellent absorption performance was attributed to the 3D reticular structure composed of SiC fibers, HfC bulk, and HfC nanoparticles, which significantly increased the number of pores and heterogeneous interfaces in the material. These microinterfaces induced interface polarization effects, thereby effectively enhancing the EM absorption. As the temperature increased, the EM absorption performance declined. At 900°C, the HS30 sample exhibited an EAB of 1.18 GHz from 12.4 to 13.58 GHz and an RLmin of 22.6 dB at 13.0 GHz. This research provides references for understanding the effects of material composition and structure on EM absorption performance.

Boron nitride nanosheets composite SiC fibers with enhanced mechanical properties and high‐temperature resistance

Boron nitride nanosheets composite SiC fibers with enhanced mechanical properties and high‐temperature resistance

Paste extrusion‐based 3D printing of fiber‐reinforced ultra high‐temperature ceramics

AbstractUltra–high‐temperature ceramics (UHTCs) are valued for their extremely high melting temperatures and resistance to active oxidation. However, their low fracture strengths and the difficulties in shaping them into complex geometries hamper their widespread application. This study aims to fabricate zirconium diboride–silicon carbide (ZrB2‐SiC) composites reinforced with aligned SiC fibers by formulating suspensions containing a preceramic polymer, ZrB2, and SiC fibers. This study assessed the influence of fiber alignment on electrical and thermal conductivities, as well as on mechanical strength. The results revealed a significant enhancement in thermal conductivity, particularly when the fibers were aligned, effectively doubling it compared with the non‐aligned parts. Additionally, increasing the fiber content significantly improved the fracture strength, with composites containing 22.5 vol% fibers reaching fracture strengths over 57 MPa. However, the final values did not meet the theoretical expectations because the porosity in pyrolyzed parts exceeded 10%. Furthermore, the study demonstrated a 10‐fold increase in electrical conductivity with fiber alignment compared to that for non‐aligned composites. These results highlight the capability of paste extrusion‐based additive manufacturing in tailoring ultra–high‐temperature ceramic matrix composites (UHTCMCs) with aligned fibers, realizing their suitability for aerospace applications.

Microstructure Evolution of the Interface in SiCf/TiC-Ti3SiC2 Composite under Sequential Xe-He-H Ion Irradiation and Annealing Process.

A new type of SiCf/TiC-Ti3SiC2 composite was prepared by the Spark Plasma Sintering (SPS) method in this work. The phase transformation and interface cracking of this composite under ion irradiation (single Xe, Xe + He, and Xe + He + H ions) and subsequent annealing were analyzed using transmission electron microscopy (TEM), mainly focusing on the interface regions. Xe ion irradiation resulted in the formation of high-density stacking faults in the TiC coatings and the complete amorphization of SiC fibers. The implanted H ions exacerbated interface coarsening. After annealing at 900 °C for 2 h, the interface in the Xe + He + H ion-irradiated samples was seriously damaged, resulting in the formation of large bubbles and cracks. This damage occurred because the H atoms reduced the surface free energy, thereby promoting the nucleation and growth of bubbles. Due to the absorption effect of the SiCf/TiC interface on defects, the SiC fiber areas near the interface recovered back to the initial nano-polycrystalline structure after annealing.

Heat treatment effects on the shear performance and microstructure evolution of W-core SiC fibers

SiC fiber reinforced titanium alloy matrix composites employed in elevated temperature aeroengine components are subjected to complex loading conditions. Investigating the shear performance of SiC fibers after heat treatment can help ensure the load-carrying capability of composites at service temperatures. This study presents a novel double shear testing method for W-core SiC fibers. The shear strength and stiffness of the SiC fibers in as-received and heat-treated conditions were measured. The morphologies of SiC fibers’ shear fracture surfaces and C coatings were thoroughly analyzed. The evolution of the internal microstructure and the composition of reaction layers after heat treatments were investigated. The shear strength of W-core SiC fibers at 95% survival probability reached 588.64MPa after 200 h of heat treatment at 600°Celsius, representing a 55% improvement over both the as-received and 1100°Celsius heat-treated conditions. After heat treatment at 1100°Celsius, the reaction layer between the W core and the SiC sheath thickened exponentially due to extensive elemental diffusion, resulting in the formation of numerous Kirkendall voids. The voids facilitated crack initiation and propagation, leading to a deterioration in fiber shear performance. The insights gained in this study regarding the shear properties of SiC fibers can provide support for predicting the mechanical performance of composites under complex loading conditions.

Evaluation of the relationship between the number of surface and internal defects and stress in inorganic fibers

To better utilize the mechanical properties of ceramics fibers, it is very important to understand the ceramics fiber distribution. The strength distribution of ceramics fibers is strongly dependent on defects that are present in or on the surface of the material. When the defects are large, the location of the defects is identified by observing the fracture surface, and the strength of the material is analyzed based on the results. However, in recent years, defects in high-strength ceramics such as carbon fibers have become so small that it is very difficult to analyze the location of such defects. To overcome this problem, a defect analysis method has been developed based on the observation that the tensile strength of fibers decreases when tensile tests are performed in liquids. In this study, a new model that considers both surface and internal defects of fibers was introduced into this analysis method, and the newly developed method was applied to quantitatively separate surface and internal defects of polyacrylonitrile-based fibers, pitch-based carbon fibers, SiC fibers, and glass fibers in air, water, and organic solvents. The number of internal and external defects was expressed as a function of stress. Based on the number of defects, the influence of surface defects was significant for glass fibers, polyacrylonitrile-based carbon fibers, silicon carbide fibers, and pitch-based carbon fibers, in that order. This method is useful for analyses of surface defects in fibers.

Ultrahigh room and high − temperature mechanical properties of SiCf/SiC composites prepared by hybrid CVI and PIP methods: Effects of PIP temperature

Unidirectional (UD) SiCf/SiC composites were prepared using chemical vapor infiltration (CVI)-polymer infiltration and pyrolysis (PIP) hybrid procedure at different PIP temperatures of 1100 °C (1100PIP), 1300 °C (1300PIP), and 1500 °C (1500PIP). The effect of PIP temperature on the microstructure of each component was studied. Results showed that SiC fiber strength and interfacial shear strength (IFSS) were the main factors affecting the mechanical properties of the composite. At 1100 °C, the fiber was thermally stable and IFSS was high, due to which 1100PIP achieved ultrahigh mechanical performance with tensile strength of 901.0 ± 87.7 MPa, flexural strength of 2186.5 ± 192.5 MPa, and toughness of 80.6 ± 12.0 MPa·m1/2. At 1300 °C, IFSS decreased slightly, due to the crystallization of BN interphase. Hence, the mechanical performance of 1300PIP decreased slightly to 789.8 ± 42.9 MPa, 1935.9 ± 163.2 MPa, and 58.2 ± 4.0 MPa·m1/2, respectively. At 1500 °C, severe fiber ceramization and decrease in IFSS caused severe decline in mechanical performance to about half of that of 1100PIP. The crack could be deflected not only at the fiber/BN (F/B) interface, but also at the CVI SiC/PIP SiC (C/P) interface, due to the existence of free carbon layers at the C/P interface, which played an important role in improving the strength and toughness of the composite. 1300PIP also showed excellent strength at high − temperature. At 1350 °C and 1500 °C, its flexural strengths were as high as 1529.0 ± 73.0 MPa and 1223.1 ± 81.1 MPa, respectively. The thermal conductivity and thermal expansion coefficient were also tested. Their values were mainly affected by the grain size and thermal stabilities of the SiC fiber and PIP matrix.

Microstructure evolution and mechanical properties of SiCf/BN/SiBCN composite after high temperature thermal exposure

The present study investigates the microstructure evolution and subsequent mechanical properties of SiCfiber/BN/SiBCNmatrix composites after high temperature exposure. These composites display a non-brittle failure response under three-point bending retaining 80% of the as-processed strength, even after elevated temperature exposure up to 1350oC for 10h. This is due to crack deflection accompanied by extensive fiber pull-out. In addition, both thermodynamic modelling and phase analysis by XRD show higher matrix degradation in vacuum than in N2 atmosphere due to the lower N2 partial pressure. After thermally exposed at 1500°C, carbothermal reaction in the matrix leads to the formation of a porous composite, and the composites retains a non-brittle failure behaviour. Meanwhile, SiBCN matrix degradation and SiC fiber strength degradation occurs, which results in significant composite strength decrement. Modest increases in the fiber/matrix interfacial shear strength occur upon exposure at temperatures up to 1350°C, and then significantly reduced after expsoure at 1500oC in N2.

Hoop tensile properties and crack propagation investigation of 2D braided SiCf/SiC composite tubes: Experiments and simulations

SiCf/SiC composites are promising candidates for advanced pressurized water reactors (PWRs) fuel cladding materials due to their enhanced accident tolerance. Their mechanical properties are strongly influenced by the braided structure of continuous SiC fibers. This study fabricated SiCf/SiC composite tubes with braid angles ranging from 30° to 50°, evaluating their hoop tensile properties through expansion-due-to-compression (EDC) experiments and analyzing the damage process using finite element method simulation. Results indicate that variations in braid angles significantly affect structural density, thereby impacting mechanical strength under hoop tensile stress. Increased braid angles result in smaller pore units and higher pore density, leading to local stress concentrations and varied deflections at overlapping regions. The dynamic propagation behavior of cracks was investigated through acoustic and structural nondestructive testing methods. Finite element analysis of different braid configurations highlights the pivotal role of pore units in the initiation and propagation of hoop tensile cracks. This study enhances the understanding of toughening structures in 2D braided composites and provides a theoretical basis for future accident-tolerant fuel cladding design.

Interfacial characteristics and thermal stability of polymer-derived SiCf/Ti composite fabricated by powder hot isostatic pressing

The novel SiCf/Ti composite is prepared by hot isostatic pressing (HIP) with polymer-derived (PD) SiC fiber and powder titanium alloy as raw materials in this work. The interfacial characteristics and thermal stability of the PD SiCf/Ti composite have been systematically investigated. The interfacial properties of the PD SiCf/Ti composites are quantified to discuss the interfacial reaction mechanisms and kinetics. The results show that with the proposed HIP process, the powder matrix can be near-fully dense, and the matrix and SiC fiber are well bonded with a uniform interfacial layer. The major interfacial products are C-Ti compounds and Si-Ti compounds, which are formed by atomic diffusion reaction. During subsequent thermal exposure conditions, the interfacial layer growth is temperature-dependent and diffusion-controlled, following the parabolic relation and Arrhenius law. The frequency factor k0 is 102–103 times lower than that in the chemical vapor deposition (CVD) SiCf/Ti composites, showing better interfacial thermal stability. After thermal exposure, the element diffusion becomes significant, and the microhardness of the near-interface zone is noticeably greater than the matrix microhardness because of the atomic diffusion of C. The microhardness of both the matrix and near-interface zone reaches the highest value after 900 °C/9 h thermal exposure. It is concluded that the PD SiCf/Ti composites with good thermal stability can be successfully fabricated by powder HIP.

Understanding fiber preform effects on tensile strengths of SiC/SiC composites prepared by chemical vapor infiltration based on a unified fiber bundle bending view

SiC/SiC composites are internationally recognized as viable thermal structural materials. Grasping the strength and the complex failure mechanisms is fundamental to comprehend their mechanical behaviors. Three types of SiC fibers and four weaving architectures were employed to fabricate eight types of preform, and the SiC/SiC composites were prepared by the chemical vapor infiltration. The microstructures were analysed by Computed Tomography imaging combined with intelligent recognition, mainly the weaving architectures and pores. Cracks in multi-layered SiC matrix exhibit periodic characteristics during propagation, enabling the theoretical in-situ strength of the fiber bundle SiC/SiC units. An empirical strength formula was established, which considered factors such as fiber bending, fiber orientation, proportion of fibers in longitudinal direction, and porosity. The deviation of the predicted strength from the actual value ranged from 0.78 % to 29.51 %. A unified fiber bundle bending view to understanding fiber preform effects on tensile strengths of SiC/SiC was introduced.

Effect of temperature and oxidative atmosphere on the oxidation behavior of yttrium-containing ceramics

Yttrium-containing ceramics exhibit excellent resistance to water-oxygen corrosion, making them an attractive choice as the modified matrix for SiCf/SiC composites. However, the oxidation products of yttrium-containing ceramics are complex and vary widely in performance. In this study, YSOC ceramics, which are composed of yttrium silicate, SiO2, and SiC, were prepared using Y2O3, SiO2, SiC, and Li2CO3. This research investigated the effects of high temperatures, air oxidation, and water-oxygen corrosion on the phase compositions of YSOC ceramics. The influence of environmental factors on the synthesis and decomposition of yttrium silicate was analyzed. Moreover, the study explored the compatibility of different oxidation products with SiC. The results suggest that Y2SiO5 and Y2Si2O7 are formed through the low eutectic of SiO2, Y2O3, and Li2CO3. The high SiO2 content likely contributes to the relatively low formation temperature of Y2Si2O7. In the oxidizing environment, Y2SiO5 reacts with SiO2 to produce Y2Si2O7. Conversely, in the water vapor-containing atmosphere, Y2Si2O7 undergoes hydrolysis to form Y2SiO5. Y2Si2O7 displays a reduced elastic modulus in comparison to SiC fibers and exhibits favorable physical and chemical compatibility with SiC fibers. However, the hydrolysis of Y2Si2O7 may potentially affect the water-oxygen corrosion resistance of the ceramics. These findings will significantly advance research and enhance understanding of the water-oxygen corrosion behaviors of yttrium-containing matrix-modified composites.

Gradient-structured SiCf/SiC hybrid woven metamaterials with superior broadband absorption and high-load bearing

SiCf/SiC composites provide a possibility to achieve the structure-function integration of military stealth materials used for aircraft tail. However, how to overcome narrow-band electromagnetic wave (EMW) absorption remains challenging. Herein, based on the adjustable permittivity of SiC fibers and the flexible design of woven structures, a gradient-structured SiCf/SiC hybrid woven metamaterial (GHWMM) is engineered with three different permittivity SiC fibers. The absorbing properties and mechanisms of the GHWMM were studied by combining experiment and simulation. Benefiting from the synergistic effect of strong dielectric loss, structural loss, and impedance matching, the GHWMM harvests an average reflection loss (RL) of −12 dB (93.7 % absorptivity), with an effective absorption bandwidth (EAB, RL ≤ −10 dB) of up to 10.7 GHz in the 4–18 GHz. Surprisingly, at high temperature of 1000 °C, the GHWMM still exhibits a RL below −5 dB in most frequency bands. Moreover, the GHWMM displays excellent wide-angle incidence characteristics, while possessing a remarkable flexural strength of 226.4 MPa. This work lays a foundation for the renewal of textile structures and the preparation of large-size assemblies, which holds promising prospect for application in the field of aircraft hot end components.

Empirical formula model and process parameter optimization of two-dimensional ultrasonic-assisted grinding force based on 2.5D-Cf/SiC fiber orientation

Empirical formula model and process parameter optimization of two-dimensional ultrasonic-assisted grinding force based on 2.5D-Cf/SiC fiber orientation

Effect of Fe-Co catalysis on the temperature field distribution during the growth of 3C-SiC fibers synthesised by microwave heating

Microwave heating produce local hot spots on materials, which result in uneven heating and other issues. Regulate the microwave temperature field using different catalyst combinations such as Fe (NO3)3·9H2O and Co (NO3)2·6H2O. The electromagnetic and temperature field distributions of 3C–SiC fibers and the molecular dynamics of the SiC interfacial growth process and interfacial oxidation reaction during microwave heating in the presence of a catalyst were simulated and calculated respectively. The results show that the combination of Fe and Co at 9 wt% catalyst concentration can effectively improve the electromagnetic loss capability of SiC fibers. The Fe and Co bimetallic catalysed synthesis of 3C–SiC fibers follows a vapor–liquid–solid growth mechanism. The Fe–Si and Fe–Co–Si alloy phases can induce 3C–SiC growth along (111) crystal faces. The simultaneous exothermic reactions provide a highly catalytically active growth environment that facilitates the enhancement of microwave temperature field uniformity. This phenomenon facilitated the synthesis of 3C–SiC fibers.

A Combined Investigation of Bending Behavior of a SiC Fiber‐Reinforced Titanium Matrix Composite with Compressive and Tensile Tests

The study investigates the bending behavior and failure mechanisms of a titanium matrix composite reinforced with SiC fibers. The effects of nominal fiber volume fraction, testing temperature, and fiber position on bending behavior are evaluated. The results indicate that increasing the nominal fiber volume fraction from 19% to 50% improves average bending strength, reaching 2757 MPa at room temperature and 2596 MPa at 350 °C. Fiber position significantly influences bend strength, and composites with fibers on the concave side show greater strength than those with fibers on the convex side. Cracks in the composite specimen preferentially initiate from the bottom of the composite core rather than from the top, and fiber breakage under tensile stress is the dominant damage mechanism in the bend test. That is consistent with the lower tensile strength relative to the compressive strength of the composite.

Processing, microstructure, and mechanical properties of chopped SiC fibers reinforced ZrB2–hBN–based composites

Processing, microstructure, and mechanical properties of chopped SiC fibers reinforced ZrB₂–<i>h</i>BN–based composites

Evolution of high temperature oxidation properties of SiCf/SiCN composites with BN interphase

In this study, SiC/SiCN composites with BN interphase were prepared using chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP) methods. The evolution and related mechanisms of mechanical and microwave absorption properties of the composites after oxidation at 800 °C, 1000 °C, 1200 °C, and 1400 °C were investigated. The results showed that with the elevating of oxidation temperature, the flexural strength of SiC/SiCN composites gradually decreased, with a retention rate of 56.7 % after oxidation at 1400 °C. The main reasons for the deterioration of mechanical properties were the changes in the crystal structure of SiC fibers under high-temperature conditions and the formation of brittle SiO2 phases on the surface and interior of the SiCN matrix. With the increase in oxidation temperature, the microwave absorption performance of the composites showed an enhancing trend. The main reasons were that after oxidation treatment, the reduction of free carbon content and the formation of SiO2 film layers from the oxidation of SiC and SiCN led to a decrease in the complex permittivity of the composites, resulting in better impedance matching and dielectric loss capabilities. The contributions of BN interphase to stress dispersion, interface polarization, and oxidation protection significantly enhance the mechanical and electromagnetic absorption properties of the composites. Therefore, SiC/SiCN composites are high-temperature structural microwave absorbing materials with great application prospects.

Novel multifibrillar carbon and oxidation-stable carbon/ceramic hybrid fibers consisting of thousands of individual nanofibers with high tensile strength

In this study, multifibrillar carbon and carbon/ceramic (C/SiCON) fibers consisting of thousands of single nanofibers are continuously manufactured. The process starts with electrospinning of polyacrylonitrile (PAN) and PAN/oligosilazane precursors resulting in poorly aligned polymer fibers. Subsequent stretching leads to parallel aligned multifibrillar fibers, which are continuously stabilized and pyrolyzed to C or C/SiCON hybrid fibers. The multifibrillar carbon fibers show a high tensile strength of 911 MPa and Young’s modulus of 154 GPa, whereas the multifibrillar C/SiCON fibers initially have only tensile strengths of 407 MPa and Young’s modulus of 77 GPa, due to sticking of the nanofibers during the stabilization in air. Additional curing with electron beam radiation, results in a remarkable increase in tensile strength of 707 MPa and Young's modulus of 98 GPa. The good mechanical properties are highlighted by the low linear density of the multifibrillar C/SiCON fibers (~ 1 tex) compared to conventional C and SiC fiber bundles (~ 200 tex). In combination with the large surface area of the fibers better mechanical properties of respective composites with a reduced fiber content can be achieved. In addition, the developed approach offers high potential to produce advanced endless multifibrillar carbon and C/SiCON nanofibers in an industrial scale.

Heterogeneous components removal mechanism and grinding force model from energy aspect in ultrasonic grinding continuous fiber reinforced metal matrix composites

Continuous fiber reinforced metal matrix composites (CFMMCs) offer higher specific strength, specific modulus, and operating temperature than matrix metals due to the unique enforcement mechanism of the one-to-one scale arrangement of matrix and reinforced phases. Due to the heterogeneous characteristics between the plastic matrix and brittle fibers, the removal mechanism of CFMMCs during processing is exceptionally complex. Ultrasonic vibration-assisted grinding (UVAG) shows great advantages in machining difficult-to-cut materials (i.e., ceramics and composites) by changing the motion trajectory between grains and workpieces, effectively reducing grinding force and improving machining quality. However, little is known about the removal mechanism of UVAG for CFMMCs composed of the ductile (i.e., metal matrix) and brittle (i.e., SiC fiber) phases with highly anisotropic structure characteristics. This raises the question of how CFMMCs with heterogeneous components perform under abrasive processing and how to predict their processing forces. Hence, UVAG and conventional grinding (CG) experiments with single CBN grain were carried out on SiC fiber reinforced TC17 matrix composites (SiCf/TC17) in this work. A grinding force model considering both phases and materials structure from energy aspect was proposed. A theoretical model for suppressing SiC fiber damage has been proposed, which is expected to guide low-damage processing of brittle materials. According to the results, the removal models of CFMMCs are revealed including: i) macro fracture of SiC fiber, ii) neat fracture of SiC fiber, and iii) TC17 matrix massive adhesion on the SiC fiber. Besides, no cracks crossing fibers are observed on the subsurface of SiC fiber under both UVAG and CG due to the good support of the TC17 matrix on SiC fibers. The grinding force predicted model error decreases as ap increases. When ap is 50 μm, the errors between predicted and experimental values are 7.8 % and 9.1 % for normal forces (Fn) and tangential forces (Ft), respectively. Ultrasound suppresses the severe wear behavior of grains, thereby improving the tool life. This paper aims to comprehensively reveal the characteristics of abrasive processing of CFMMCs from various aspects (surface morphology, subsurface features, grinding force prediction, and tool wear), which will promote the industrial application of CFMMCs.