SiC Fibers Research Articles

Flexible SiC-CNTs hybrid fiber mats for tunable and broadband microwave absorption

Flexible microwave absorbers with high stability are in increasing demand for the applications under harsh conditions. SiC as a functional ceramic material has the feature of high environmental tolerance and adjustable electromagnetic (EM) absorbing properties, making them suitable to be applied for harsh environments. However, the electrical property of SiC requires to be further enhanced to obtain qualified EM absorbing performance. In this work, multiwall carbon nanotubes (CNTs) were introduced to SiC to enhance the electrical properties. Flexible two-dimensional (2D) CNTs loaded SiC fiber mats were prepared as EM absorbers via electrospinning and polymer-derived-ceramic (PDC) methods. The CNTs inside the fibers can form conductive networks and act as reinforcement to ensure high flexibility and enhance the microwave absorption properties of SiC mats. Thus, a reflection loss of −61 dB and an effective absorption band (EAB) of 2.9 GHz were obtained. More importantly, the EM absorption can be adjusted by tuning the content of CNTs and the EAB can cover the entire X-band by adjusting the material thickness. The work provided a facile strategy to fabricated flexible 2D ceramic mats with high environmental stability and tunable electrical properties, which may shed light on the production of reliable EM absorber for broadband EM absorption applications.

Microstructure characteristics of C+ and He+ irradiated SiCf/SiC composites before and after annealing

The microstructures of SiCf/SiC composites irradiated with 400 keV C+ and then 200 keV He+ at 633 K and annealed post-irradiation at 1073, 1273, and 1473 K for 5 h were analyzed. The SiCf/SiC composites were composed of nanocrystal SiC fibers with 5–25 μm in size, SiC matrix with a columnar crystal structure, and six transition layers (alternate distribution of pyrolytic carbon and SiC layers) between them. Several fine microcracks induced by irradiation appeared at the interfaces and grew during annealing. An irradiation band with a few helium bubbles was formed in the SiC fiber and had a width of approximately 260 nm, which decreased with increase in annealing temperature. Annealing caused the irradiation-induced bubbles to grow and induced a linear arrangement of the bubbles in the SiC fiber. Larger He bubbles were generated at the grain boundary and tended to form microcracks in the SiC matrix. Irradiation did not cause obvious amorphization at 633 K and annealing did not induce nanograin growth. After irradiation, the area fraction and size of carbon packets with graphitic nature in the SiC fiber decreased.

A high-temperature structural and wave-absorbing SiC fiber reinforced Si3N4 matrix composites

The SiCf/Si3N4 composite with low–high–low permittivity sandwich structure was designed for high-temperature electromagnetic (EM) wave absorption and mechanical stability. The SiCf/Si3N4 possessed the remarkable mechanical properties at room temperature (the flexural strength is 357 ± 16 MPa and the fracture toughness is 10.8 ± 1.7 MPa m1/2) for the strong fiber strength, moderate interface bonding strength and uniform matrix. Furthermore, the retention rate is as high as 80% at 800 °C. The A/B/C nanostructure and the sandwich meta-structure endowed the SiCf/Si3N4 with an excellent EM absorbing property at room temperature. The SiCf/Si3N4 still absorbed 75% of the incident EM waves energy in X and Ku bands when the temperature increases up to 600 °C, which is only 6% lower than that at room temperature, for the partial compensation of the decreased interfacial polarization loss for the increased conductivity loss and dipole polarization loss.

Dielectric response and microwave absorption properties of SiCw/SiCf composites derived from carbon fiber

The SiCw/SiCf composites composed by SiC whiskers with core–shell structure and SiC fiber with alike-array structure were prepared without growth catalyst, hydrogen silicone oil (H-PSO) as raw material, carbon fiber as the matrix. SiC fibers act as supports for a nanomesh containing interconnected one-dimensional SiC whiskers. The results of studying the absorption properties of the Ku band show that the density of stacking faults decreases and the aspect ratio increases as the heat treatment temperature increases and they jointly affect the dielectric properties of the SiCw/SiCf composites. The minimum reflection loss of the SiCw/SiCf composites obtained at 1400 °C can reach − 29.75 dB when the absorber thickness is 3.0 mm, and the effective bandwidth is 2.25 GHz. The polarization relaxation and interfacial polarization in the unique structure improve the microwave absorption properties and broaden the absorption frequency.

Thin coatings of hafnon abate oxidative recession of SiC fibers

AbstractThe oxidation behavior of SiC fibers coated with (a) undoped polysilazane and (b) precursors containing a mixture of polysilazane and hafnium butoxide in equal weight fractions, is reported. The coatings were prepared by repetitive cycles of nanolayer depositions, as reported in recent publications. The oxidation experiments were carried out at 1400°C in ambient air (Boulder, CO) for up to 100 hours. The extent of degradation of SiC was measured by the recession in the diameter of the fibers as a function of time. The fibers with undoped polymer precursor recessed significantly, whereas the fibers coated with HfSiCNO remained essentially unchanged. These results are in agreement with earlier work from our laboratory where the resilience of hafnon and zircon, as well as hafnia and zirconia, against high‐temperature corrosion in streaming humid environments had been highlighted.

Development of polymer-derived SiC fiber

The polymer—derived SiC fiber is one of the most important reinforcing materials for high performance ceramic matrix composites (CMC). Three generations of SiC fibers have been developed over the past thirty years. In this article, the preparing methods, compositions, microstructures and performances of three generation fibers are reviewed. Furthermore, the relationships are discussed between microstructure and the main properties of the fibers, such as high temperature-resistance and creep resistance. as a summary, some improving methods for the properties of SiC fibers derived from precursor are summarized.

Study on ZrB2-Based Ceramics Reinforced with SiC Fibers or Whiskers Machined by Micro-Electrical Discharge Machining.

The effects of different reinforcement shapes on stability and repeatability of micro electrical discharge machining were experimentally investigated for ultra-high-temperature ceramics based on zirconium diboride (ZrB2) doped by SiC. Two reinforcement shapes, namely SiC short fibers and SiC whiskers were selected in accordance with their potential effects on mechanical properties and oxidation performance. Specific sets of process parameters were defined minimizing the short circuits in order to identify the best combination for different pulse types. The obtained results were then correlated with the energy per single discharge and the discharges occurred for all the combinations of material and pulse type. The pulse characterization was performed by recording pulses data by means of an oscilloscope, while the surface characteristics were defined by a 3D reconstruction. The results indicated how reinforcement shapes affect the energy efficiency of the process and change the surface aspect.

Magnetic sputtering of FeNi/C bilayer film on SiC fibers for effective microwave absorption in the low-frequency region

It is a great challenge in promoting a microwave absorber with excellent absorbing properties in the low-frequency region. Herein, SiC fibers (SiCf) coated by a bilayer of FeNi/C (SiCf/FeNi/C) are fabricated via a two-step magnetron sputtering method. Owing to the improved dielectric loss, magnetic loss, and impedance matching, the reflection loss of SiCf/FeNi/C is remarkably enhanced. Accordingly, the minimum reflection loss of SiCf/FeNi/C reaches −26.18 dB at a low-frequency region of 3.44 GHz. Besides, the mechanic strength of SiCf/FeNi/C maintains at 2.32 GPa as compared to as-received SiCf. Thus, SiCf/FeNi/C is expected to be an ideal structure material to meet low-frequency microwave absorption requests.

Development of SiC fiber through heat treatment of silica aerogel by in-situ curing

In this study we invented a new way to fabricate SiC fiber by In-situ curing of silica aerogel. At first, silica aerogel was introduced as supporting structure and silicon source to fabricate the graphite preform. Then the obtained preform was sintered at high temperature under inert atmosphere, through which SiC fiber could be successfully obtained. The preparation process and inner structure of SiC fiber were discussed.

Interfacial reaction and brazing behaviour of SiCf/SiC with Cf/C composites using Si-10Zr alloy at high temperatures

A Si-Zr eutectic alloy was employed as a high-temperature braze filler to join SiCf/SiC composites with Cf/C composites. The interfacial microstructure and bonding mechanism on the side of the SiCf/SiC composites were studied for the first time. The results showed that SiC reaction layers formed between the Si-Zr filler and both substrates. The SiC layer resulted from the chemical reaction between Si and C at the filler–Cf/C interface. In contrast, at the filler–SiCf/SiC interface, coarse-SiC crystals only precipitated on the SiC fibre bundles, and there was only non-reactive bonding between the filler and the SiC matrix. In addition, the reactive infiltration process between the liquid Si alloy and the porous substrates contributed to the formation of infiltration structures, including Cf/C–SiC and SiCf/SiC–Si-ZrSi2, resulting in the reinforcement of the substrates and the joint. Finally, a favourable shear strength of 38 MPa was achieved.

Bending Properties and Failure Mechanism of Continuous W-Core-SiC Fiber-Reinforced 2024 and 6061 Aluminum Matrix Composites

In order to investigate the effect of different matrices on the bending properties and fracture behavior of the continuous W-core-SiC fiber-reinforced aluminum matrix (SiCf/Al) composites, 30 vol.% SiCf/2024Al and 30 vol.% SiCf/6061Al composites were prepared via matrix coating and hot isostatic pressing. Samples from these composites were subjected to the push-out test and three-point bending test with in situ SEM. The microstructure of the SiCf/Al composites was examined by SEM and TEM. Results showed that there were coarse AlCuFeMn and Al2Cu phases in the matrix of the SiCf/2024Al composite, and needle-like Al4C3 phase at the interface between fiber and matrix. For the SiCf/6061Al composite, there were no coarse second phase in the matrix and no Al4C3 phase at the interface between fiber and matrix. The interfacial shear strength of the SiCf/2024Al composite (~ 37 MPa) was relatively larger than that of the SiCf/6061Al composite (~ 34 MPa), indicating a relatively strong interface bonding for the SiCf/2024Al composite. The bending strength of the SiCf/6061Al composite (1091 MPa) was superior to that of the SiCf/2024Al composite (968 MPa). For 30 vol.% SiCf/2024Al composite, cracks were initiated at the edge of the coarse second phase under bending load and propagated along the grain boundary of matrix. The crack passed directly through SiC fibers due to the strong interface bonding and needle-like Al4C3 phases formed by interfacial reaction, and the propagation rate was fast. For 30 vol.% SiCf/6061Al composite, the crack was initiated at the interface between fiber and matrix when the plastic deformation of matrix was retarded at the first SiC fiber. Then, the crack passed around SiC fibers and propagated in forms of crack bridging and deflection due to the suitable interface bonding, and the propagation rate was slow.

SiC/SiC mini-composites with yttrium disilicate fiber coatings: Oxidation in steam

Solutions of YPO4 were used to precipitate YPO4 on pre-oxidized Hi-Nicalon-S SiC fibers. Tows of the coated fibers were then infiltrated with a preceramic polymer loaded with SiC particles to form mini-composites. During pyrolysis of the matrix, SiO2 and YPO4 on the fibers reacted and formed a Y2Si2O7 fiber matrix interphase. Mini-composites were exposed to steam at 1000 °C for 10, 50, and 100 h, tensile tested, and the effect of oxidation in steam on the functionality of the Y2Si2O7 fiber coating was investigated. The minicomposites oxidized at 1000 °C for 10 h retained 100 % of their unoxidized strength, and those oxidized for 50 and 100 h retained 92 % and 90 % of unoxidized strength, respectively. Strength retention and fiber pullout in both unoxidized and oxidized minicomposites suggests that the Y2Si2O7 interphase was effective in maintaining a weak fiber-matrix interface.

Mechanical properties and strengthening mechanism of SiCf/SiC mini-composites modified by SiC nanowires

The effects of the SiC nanowires (SiCNWs) and PyC interface layers on the mechanical and anti-oxidation properties of SiC fiber (SiCf)/SiC composites were investigated. To achieve this, the PyC layer was coated on the SiCf using a chemical vapour infiltration (CVI) method. Then, SiCNWs were successfully coated on the surface of SiCf/PyC using the electrophoretic deposition method. Finally, a thin PyC layer was coated on the surface of SiCf/PyC/SiCNWs. Three mini-composites, SiCf/PyC/SiC, SiCf/PyC/SiCNWs/SiC, and SiCf/PyC/SiCNWs/PyC/SiC, were fabricated using the typical precursor infiltration and pyrolysis method. The morphologies of the samples were examined using scanning electron microscopy and energy dispersive X-ray spectrometry. Tensile and single-fibre push-out tests were carried out to investigate the mechanical performance and interfacial shear strength of the composites before and after oxidization at 1200 °C. The results revealed that the SiCf/PyC/SiCNWs/SiC composites showed the best mechanical and anti-oxidation performance among all the composites investigated. The strengthening and toughening is mainly achieved by SiCNWs optimization of the interfacial bonding strength of the composite and its own nano-toughening. On the basis of the results, the effects of SiCNWs on the oxidation process and retardation mechanism of the SiCf/SiC mini-composites were investigated.

Scheelite coatings on SiC fiber: Effect of coating temperature and atmosphere

Scheelite coating was deposited on SiC fiber tows from various liquid-phase precursors followed by heat treatments between 900 °C and 1100 °C in different atmospheres. The tensile strength was fully retained for the coated fibers treated at 900 °C in vacuum. Subsequent heat treatment at 1100 °C in Ar had little effect on the fiber strength, which is explained by the excepted good thermal stability between the scheelite coating and SiC fiber. However, larger strength degradation and poor spool ability of coated fibers prepared in Ar/air were found. Assisted oxidation of SiC fiber by calcium salts is suggested to be responsible for the much larger strength degradation of fibers prepared in Ar/air.

SiC-Fiber Reinforced Silicon Carbide-Based Ceramic Composite

Dense silicon carbide-based ceramic composites reinforced with SiCf fiber have been produced by hot pressing at a temperature of 1850°C. The reinforcing agent used was silicon carbide fiber produced by siliciding carbon cloth with SiO vapor. It has been shown that raising fiber content from 1 to 7 wt % increases the density, bending strength, and fracture toughness of the material, which reach ρ = 3.20 ± 0.01 g/cm3, δb = 450 ± 26 MPa, KIс = 5.6 ± 0.1 MPa m1/2 at 7 wt % SiC fiber.

Oxidation behavior of 3D SiCf/SiBCN composites at 800–1200 °C

3D SiCf/BN–SiC/SiBCN composites were fabricated via precursor impregnation and polymer infiltration pyrolysis (PIP). Oxidation behavior of the composites heated in air at 800 °C, 1000 °C and 1200 °C for 50 h was investigated. Following the oxidation treatment, it was found that the bending strength of the composites at different oxidation temperatures was degraded. The weight loss of the composites decreased gradually over the range of oxidation times of 1–50 h. In order to clarify the oxidation mechanism of the composites, reconstructed images, microstructures, phase compositions, the oxide layer formed on the composites and main chemical reactions were all analyzed. It was revealed that the degradation in the fracture strength of the composites was closely related to the oxidation of SiBCN matrix and BN-SiC interphase, whereas there was no signs of oxidation products about SiC fiber, which indicated that SiC fiber could be protected from oxygen by SiBCN matrix at 800−1200 °C in air.

Influence of porosity on anisotropic thermal conductivity of SiC fiber reinforced SiC matrix composite: A microscopic modeling study

The effect of porosity on the effective thermal conductivities calculation for continuous SiC fiber reinforced SiC matrix composites (SiCf/SiC) was studied in this work by finite element modeling. A three-dimensional representative volume element (RVE) containing detailed geometric features (fibers, matrix, fiber coatings and pores) was generated to rebuild the microstructure of SiCf/SiC and used to numerically calculate the effective transversal and longitudinal thermal conductivities of SiCf/SiC. Markworth model and parallel model were chosen as theoretical models to calculate the transversal and longitudinal thermal conductivities respectively. The numerical results obtained by RVE models were validated by comparison with the theoretical and experimental results. The results highlight the existing theoretical models cannot well predict the transversal thermal conductivity of SiCf/SiC with the existence of pores. In the analysis of the effect of porosity, real pore structure in SiCf/SiC was investigated to revel the relationship between porosity and the effective thermal conductivities. In the case of longitudinal thermal conductivity, the parallel model plus the linear term of porosity can still be used to predict the longitudinal thermal conductivity. As for the transversal thermal conductivity, a more proper Markworth model for SiCf/SiC transversal thermal conductivity calculation calibrated by incorporating porosity is proposed to efficiently calculate the transversal thermal conductivity at the end of this paper.

Fiber-supported alumina separator for achieving high rate of high-temperature lithium-ion batteries

More and more application scenarios of rechargeable batteries like lithium-ion batteries are set up in high-temperature environments, such as large-scale energy storage, aerospace, oil extraction industry, etc. Besides of electrolyte, the separator is also a vital part of the battery's sustainable operation at high temperature working condition, however traditional polyolefin separators and even ceramic-coated polyolefin separators have poor thermal stability. This article provides a fiber-supported aluminum oxide separator with improved flexibility and thermal stability because of the introduced flexible SiC fiber network skeleton. The ceramic separator exhibits electrochemical performance equivalent to commercial separators at room temperature. What's more, with high-temperature electrolyte system, its conductivity at 120 °C reaches 5.12 mS cm−1, which is 3 times higher than that at room temperature, so that the LiFePO4 half-cell has excellent rate performance that still maintains a specific capacity of 140 mAh g−1 for 200 cycles under a rate of 20C at 120 °C. Specially, the half-cell containing the high temperature stable fiber-supported aluminum oxide separator realizes cycles of charging at a high temperature with high rate as 20C and discharging at a room temperature with normal rate of 1C, which is of great guiding significance to practical application.

Low-cycle fatigue behavior and damage progression of a fiber reinforced titanium matrix composite

The low-cycle fatigue behavior and damage progression of a SiC fiber reinforced Ti–6Al–2Sn–4Zr–2Mo-0.1Si matrix composite was investigated systematically. The fatigue life increased from 4 to 52388 cycles when the maximum stress decreased from 1500 MPa to 1100 MPa. The modulus calculated from the stress-strain response exhibited little variation for all the specimens during the fatigue process. Fractographic observations showed that the fatigue cracks initiated internally and propagated preferentially in the internal sputtered matrix instead of the unreinforced matrix in the external layer for the cylindrical specimen. The proportion of the fatigue region in the fracture surface increased as the applied stress level decreased. The internally-progressed damage, especially breaks of bridging fibers, was well characterized in situ by the acoustic emission system.

Effect of different kinds of SiC fibers on microwave absorption and mechanical properties of SiCf/SiC composites

The SiC fibers are essential for designing microwave absorption and mechanical properties of multifunctional composites. In this study, SiCf/SiC composites were fabricated by SLF, KD-II, and KD-S SiC fibers. The SLF fibers are composed by amorphous SiOC. The KD-II and KD-S fibers reveal higher crystallizations. The conductivity of SLF, KD-II, and KD-S SiC fibers are 0.0127, 1.184, and 0.1316 S/cm, respectively. The flexural strength of SLF, KD-II, and KD-S SiCf/SiC composites are 147.77, 322.57, and 248.16 MPa, respectively. With the thickness of 2.3 mm, the microwave absorption property of SLF SiCf/SiC composites is over − 25 dB in X band. Additionally, the effective absorption bandwidth (EAB) of SLF SiCf/SiC composites below − 10 dB reaches 3.72 GHz with the thickness of 2.7 mm. In contrast, the KD-II SiCf/SiC composites only reach − 3.6 dB in X band when the thickness varies from 2 to 2.9 mm. With the thickness of 2 mm, the microwave absorption property of KD-S SiCf/SiC composites is over − 9 dB. With the thickness of 2.2 mm, the EAB of KD-S SiCf/SiC composites below − 7 dB reaches 4.12 GHz. The mechanisms of mechanical, microwave absorption, and penitential applications for SiCf/SiC composites are also discussed.