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This study objective is a proposal of a new lightweight and affordable structural material with heat resistance of 600–1000°C. We developed process technology and evaluated the mechanical properties of SiC fiber (Hi‐Nicalon)/Si‐CoSi2 matrix composites. After Hi‐Nicalon fibers were woven into orthogonal three‐dimensional fabrics (Vf${{V}_f}$ 40%), a carbon layer (FB‐C) was formed on the fiber surface using film boiling, serving as the fiber–matrix interface layer. To suppress Hi‐Nicalon strength degradation, Si‐22 at.% Co alloy with a lower melting point compared to pure Si was infiltrated at 1380°C to produce Hi‐Nicalon/FB‐C/Si‐CoSi2 matrix composites. Dense composites with no open pores were obtained. Their bulk density was 2.7 g/cm3. Their mean value of four‐point bending strength was 460 MPa at room temperature and 612 MPa at 800°C in an Argon atmosphere. Fiber pullout and fiber bridging were observed clearly on the fracture surfaces. The FB‐C, with an average thickness of 4 µm, suppresses Hi‐Nicalon damage from the molten Si‐Co alloy. Furthermore, an inexpensive oxidation‐resistant coating of Si‐Co alloy dispersed with TiB2 and SiC particles was formed on the composite surface. The four‐point bending strength in air was 424 MPa at 800°C and 539 MPa at 1200°C, demonstrating that the oxidation‐resistant coating functions effectively. [ABSTRACT FROM AUTHOR]

If the temperature and environment effects on the oxidation of SiC fibers have been extensively documented, the impact of external stresses (stress‐oxidation coupling effect) remains questioned. Therefore, interrupted static fatigue tests were conducted on filaments. Surviving specimens (>60%) were subsequently tensile tested and fracture surfaces recovered for analysis. The external stress was found to have no impact on the oxidation regime (linear or parabolic) nor on its rate, which is comparable to literature data. As long as the slow crack growth (SCG) incubates (negligible growth rate), the oxidation was shown to govern the embrittlement. Fracture surface analysis revealed tensile residual stresses, attributed to a wedge effect when specimens were unloaded. Rare tests (<2%) were interrupted while the crack had significantly grown highlighting the successive crack fronts. Sources of residual stresses and differences between fiber types (flaw position inducing a bias on lifetime prediction) are discussed. In these circumstances, a coupling effect between the oxidation embrittlement and the SCG could be assumed for moderate stress levels, which is pertinent for most of ceramic matrix composite applications. [ABSTRACT FROM AUTHOR]

In this work, the Yb2Si2O7 interphase was prepared on SiC fibers using the sol–gel method. The influence of sol concentration on the morphology of the interphase was discussed. After heat treatment in argon at 1200°C for 1 h, the Yb2Si2O7 was grown in situ on the fiber surface, forming an interphase layer. Then, SiCf/Yb2Si2O7/SiC minicomposites were prepared by chemical vapor infiltration (CVI). The Yb2Si2O7 interphase exhibited no changes throughout the high‐temperature preparation process and maintained stability and compatibility with the fiber and matrix. The tensile strength of SiCf/Yb2Si2O7/SiC minicomposites with Yb2Si2O7 interphase was significantly higher than SiCf/SiC minicomposites without interphase. The crack deflection, interfacial debonding, and fiber pullout were observed in the tensile fracture of the SiCf/Yb2Si2O7/SiC minicomposites. [ABSTRACT FROM AUTHOR]

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Microwave heating is considered an environmentally friendly and cost-effective method for sintering. Temperature field regulation and local hotspots are gaining widespread attention during microwave sintering. In this study, sol-gel method was employed to synthesize SiC fibers via microwave heating by uniformly combining the raw materials with Cu and Ni catalysts. The thermal effects and growth mechanisms of SiC were investigated using COMSOL Multiphysics software and DFT calculations for samples with Cu and Ni catalysts, respectively. The occurrence of magnetic losses played a significant role at low temperatures in the samples with Ni catalyst, resulting in the formation of local hotspots and the formation of molten Ni–Si alloys.Whereas, a reflection effect was observed in the samples with Cu catalyst, resulting in a more uniform temperature distribution. The V-L-S growth mechanism was identified in the SiC fibers synthesized with Ni catalyst during microwave heating, while the V–S growth mechanism was observed in the SiC particles synthesized with Cu catalyst. [ABSTRACT FROM AUTHOR]

Strong, tough, and almost fully dense unidirectional SiC f /BSAS composites were obtained through the slurry infiltration and hot-pressing process. The 0.75BaO-0.25SrO-A1 2 O 3 -2SiO 2 mixed precursor synthesized by solid state reaction from metal oxides was utilized as the matrix slurry. SiC fibers with BN/C/SiN x /C coating served as reinforcements. During hot pressing, the monoclinic celsian phase in the matrix was produced in situ. The composite exhibited graceful failure in three-point bend tests at room temperature. The flexural strength and strain reached 315.37 MPa and 0.44 %, respectively. With the help of the BN/C/Si 3 N 4 /C coating, the SiC fibers occur debonding and pull-out, exhibiting outside debonding features. After annealing in O 2 at 850 °C for 10 h, the strength retention rate of the composites was 95.41 %, showing excellent stability for in thermal structural components. [ABSTRACT FROM AUTHOR]

SiC-based fibers are key constituents for the reinforcement of SiC/SiC thermo-structural composites. Their tensile strength is however known to decrease if oxidized because of stresses associated to the oxide scale growth, which in turns is affected by the fiber type (chemical composition, microstructure). This phenomenon is here reported for several types of fibers (five in total, Nicalon® or Tyranno®) between 450 and 950 °C in ambient air. The highest strength loss rate was noticed on Tyranno® Grade S, also known to be more sensitive to oxidation. The initial strength was nevertheless recovered when the oxide scale was removed. This report uses a simplistic empirical model to fit the embrittlement phenomenon, relating the tensile strength to x −1/2. The strength distribution and the projection to larger scale thicknesses are discussed. Assuming the same conditions (environment, scale crystallization rate), the oxidation kinetic could be used to estimate the embrittlement phenomenon. [Display omitted] • On top of oxide scale growth, the oxidation of SiC filaments reduces their tensile strength. • Strength proportional to x−1/2, where x is the oxide scale thickness. • Analysis of the fracture pattern did not revealed stresses at the scale-fiber interface. • The strength dispersion tends to become broader on oxidized fibers. • Introduction of flaw size-dependent geometrical factor to solve projection inconsistency. [ABSTRACT FROM AUTHOR]

For this study, orthogonal three dimensional (3D) woven silicon carbide (SiC) fiber (Hi-Nicalon, Hi-Nicalon Type S) -reinforced Si-CoSi2 matrix composites (SiC fiber/Si-CoSi2 composites) were fabricated and the microstructures and mechanical properties were characterized. The SiC fibers (28% fiber volume fraction) woven into orthogonal 3D fabrics and used as reinforcement were coated with chemical vapor infiltration (CVI)-carbon to control the fiber–matrix interface. The composite material infiltrated with Si-CoSi2 was produced using a melt-infiltration process. Four-point bending tests conducted at room temperature showed bending strength exceeding 300 MPa and tensile fracture strain exceeding 0.7%. Furthermore, bending strength greater than 400 MPa was found from a high-temperature four-point bending test under an Ar atmosphere. The failure mode was quasi-ductile. Fiber pull-out and fiber cross-linking were observed clearly. Melt infiltration of the Si-Co alloy caused little damage to the SiC fibers, confirming CVI-C layer protection of the fibers during melt infiltration and confirming that the layer can control mechanical properties at the fiber–matrix interface. [ABSTRACT FROM AUTHOR]

Continuous SiC fibers reinforced SiC ceramic matrix composites have wide applications in the aerospace and nuclear fields owing to their excellent high-temperature resistance, good oxidation resistance and mechanical properties. The precursor-derived method has been the most important method for preparing continuous SiC fibers. The introduction of specific hetero elements could effectively improve properties of SiC fibers. Based on the research work on precursor-derived SiC fibers of high performance carried out by our group in the past forty years, this review firstly summarizes the addition methods of hetero elements, mainly including physical blending or chemical modification methods; The role and mechanism of hetero elements have been elucidated from several aspects: increasing the ceramic yield of the precursor, facilitating densification during sintering of the precursor-derived SiC fibers, improving high-temperature resistance of the final SiC fibers, and generating functions of SiC fibers; The composition, microstructure, properties, and developmental status of SiC fibers containing hetero elements, such as Ti, Al, Zr, Fe, B, as well as refractory metals (Hf, Ta, Nb), have been introduced. Furthermore, future research in the development of precursor systems, quantitative study of the relationship between the types and contents of hetero elements and properties of derived fibers, as well as engineering applications of the precursor-derived SiC fibers, has been prospected.

In current work, irradiation-induced microstructural evolution of the Cansas 3303 SiC fiber was investigated. This fiber was irradiated by 1.8 MeV argon ions at room temperature in the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. The ion fluences were 5 × 1014, 1 × 1015, 2.5 × 1015 and 5 × 1015 ions/cm2 corresponding to the maximum doses of 0.27, 0.54, 1.35 and 2.70 displacements per atom (dpa), respectively. Irradiation effects were characterized by using micro-Raman spectroscopy and transmission electron microscopy. The results showed that the Cansas 3303 fiber consists of nanocrystalline SiC grains, carbon packets and carbon ribbons. Irradiation-induced amorphization accompanied with the decrease of SiC grain size was observed in the fiber with the increase of ion fluences. However, SiC grains still remained in this fiber up to the dose of 2.70 dpa. Besides, the reduction of the quantity and size in carbon packets and the annihilation of carbon ribbons in this fiber were also detected. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The oxidation behavior of Tyranno® Grade-S SiC-tows was investigated under ambient air in the 450–1140 °C range. Below 650 °C, a linear oxidation rate was identified for oxide scale thicknesses up to 1.2 µm, attributed to the hydroxyl (Si-OH) groups degrading the silica structure as shown by 1H and 1H–29Si CP/MAS NMR. Above this temperature, the classical parabolic oxidation rate (diffusion controlled) was identified with a dehydroxylated silica scale. These results bring new insights to interpret the slow crack growth (SCG) transition observed at 650 °C. Above 650 °C the activation energies (Ea) for oxidation and SCG are close to 50 kJ mol−1 indicating the diffusion might be the rate limiting factor; whereas for lower temperatures Ea SCG < Ea oxidation as a consequence of the stress-enhanced chemical reactivity. The oxide thicknesses at failure time (predicted with power or exponential laws) were assessed and highlight some incoherencies in the lifetime projection to lower stresses. [Display omitted] • Oxidation kinetics for Grade S fibers under ambient air from 450° to 1140°C. • Oxidation rate below 650 °C exclusively linear, regardless of silica thickness. • Dehydroxylation of the silica shell observed from 550° to 950°C. • Identical SiO 2 growth rate under static oxidation and static fatigue conditions. • Ea ox ≈ Ea SCG (slow crack growth) above 650 °C and Ea ox > Ea SCG below 650 °C. [ABSTRACT FROM AUTHOR]

SiC fiber is one of the common reinforcements for ceramic matrix composite (CMC) due to its superior characteristics such as low density, high tensile strength, excellent high temperature resistance and oxidation resistance. The preparation of coating on the surface of SiC fiber can not only improve the mechanical properties, high temperature resistance, oxidation resistance and electromagnetic functional properties of the fiber itself, but also effectively improve the bonding properties of the interface between the fiber and the matrix to promote the fracture toughness and mechanical properties of the composite. The preparation methods of surface coatings on SiC fiber were firstly reviewed in this paper by elaborating on the basic processes and related research progress of etching, deposition, chemical vapor infiltration, and precursor derived methods, and the advantages and disadvantages of different preparation methods were compared. Then the effects of coatings on SiC fibers and their reinforced composite materials were reviewed. Finally, the development trend of surface coating on SiC fibers was briefly summarized. The combination of experimental research and computational simulation can be used to simulate the real service environment of SiC fibers coatings, and the performance of fibers under extreme service conditions can be improved by preparing thermal barrier composite coatings.

The BN coating was deposited on the surface of typical domestic SiC fibers by chemical vapor permeation (CVI) process, and the fibers were oxidized at 800-1200 ℃ for 1 h. The morphology, structure and composition of BN coated SiC fibers after oxidation were characterized. The property changes of BN coated SiC fibers after oxidation were evaluated by tensile strength of monofilament. The results show that when the oxidation temperature is lower than 1000 ℃, the BN coating and its oxide can effectively prevent the erosion of the inner SiC fibers by O2, and when the temperature continues to rise, the SiC fibers are oxidized. With the increase of oxidation temperature, the surface oxide of BN coated SiC fibers goes through the process of α-B2O3→SiCxOy→amorphous SiO2. The tensile strength of BN coated SiC fibers decreases with the increase of oxidation temperature. Direct exposure of BN coating to oxidizing environments reduces the oxidation resistance of SiC fibers. The failure source of fiber fracture first transitions from BN coating defects to B2O3 oxide layer defects and finally evolves into SiO2 oxide layer porosity defects.

SiC fibers play an essential role in determining the mechanical properties of ceramic matrix composites. This study examines the influence of different heat treatment atmospheres at 1600 °C on the microstructural and mechanical behaviors of SiC–ZrC fibers. Experimental results demonstrate a general decline in the fibers' mechanical performance, with a reduction of 31.49% in a vacuum environment and 39.36% in an argon atmosphere. Under vacuum conditions, the amorphous phase within the fiber decomposed, leading to an increased crystallinity; however, no significant clustering of the ZrC phase was observed. In contrast, under argon conditions, the amorphous phase of SiC–ZrC underwent decomposition, accompanied by the clustering of ZrC particles, resulting in the fiber exhibiting inferior mechanical properties compared to those treated in a vacuum. In summary, doping ZrC in the fibers enhances microstructural stability under vacuum conditions, suppressing the decomposition of the SiC x O y phase. However, post heat-treatment in an argon environment led to ZrC clustering, adversely impacting the fiber's mechanical performance. [ABSTRACT FROM AUTHOR]

The implementation of in situ carbon nanotube growth on fibers is regarded as a proficient strategy for enhancing the electromagnetic wave (EMW) absorption capabilities of the fibers. However, the introduction of magnetic properties to the fibers and the adjustment of their impedance matching still present significant challenges. In this study, the deposition of uniform arrays of carbon nanotubes (CNTs) onto SiC fibers was successfully achieved through chemical vapor deposition. Subsequently, a FeNi coating was applied to the CNT arrays using the magnetron sputtering technique, as confirmed by SEM and TEM analyses. Furthermore, the SiC f /CNT@FeNi composites exhibited improved EMW absorption characteristics. With a thickness of 2.5 mm, the reflection loss was optimized, attaining an impressive value of −63.4 dB at 16.03 GHz, while the effective frequency bandwidth spanned 6.26 GHz (ranging from 11.74 to 18 GHz). Notably, the radar cross-section (RCS) was reduced by 21.64 dB m2. The enhanced EMW absorption performance of the SiC f /CNT@FeNi composites can be attributed to the incorporation of FeNi-modified CNT arrays, which effectively amplify Debye dipole polarization and optimize the impedance matching of the SiC fiber. This approach paves the way for the fabrication of EMW absorption materials exhibiting superior performance. [ABSTRACT FROM AUTHOR]

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A novel SiC/SiOC composite was prepared via the polymer infiltration and pyrolysis (PIP) process by using a low-cost poly-methyl-silsesquioxane resin as matrix precursor and continuous thin SiC fibers as reinforcements. A carbon coating is in situ formed on SiC fiber prior to the composite processing. The high yield of the resin resulted in a short period of the composites achieving densification. The composites exhibited pseudoplastic fracture with a high flexural strength of 315.10 MPa and a fracture toughness of 21.6 MPa m1/2. With the help of the in situ coating, the SiC fibers pulled out of the matrix independently, leading to optimization of the reinforcing effect and enhancement of the composite strength compared to chemical vapor deposition (CVD) fiber coatings. After annealing in N 2 at 1000 °C for 10 h, the strength retention rate of the composites is 92.21%, showing excellent stability to be used in thermal structural components. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BN and BN/SiC coatings were deposited on the surface of two typical domestic SiC fibers by CVI process, and the composition of coatings was analyzed. The tensile strength of monofilaments was evaluated by Weibull distribution, and the tensile fracture failure behaviors of the fiber before and after depositing coatings were studied. The results show that the carbon-rich layer with appropriate thickness (15 nm) can heal the defects on the surface of SiC fiber and reduce the possibility of fiber failure from the surface. The thickness of the coating prepared by the CVI process is uniform and the composition is stable. After depositing BN and BN/SiC coatings, the tensile strength and elastic modulus of the two kinds of SiC fibers are decreased. BN coatings can also repair the surface defects of the fiber, so that the fiber strength distribution tends to be concentrated. Different from the uncoated fibers, the tensile fracture failure sources of coated fibers are the surface defects of BN and SiC coatings, respectively.

The near stoichiometric SiC fiber has been reported to play significant roles in the application of aeroengine field. An in‐depth understanding on the degradation mechanism of the fiber during its corrosion in air and under a simulated aeroengine environment (PH2O:PO2:PAr = 14:8:78 kPa) will shine a light on the performance evaluations of the near stoichiometric SiC fiber‐based materials as well as the development of their potential applications. In this study, X‐ray diffraction, scanning electron microscope, and FIB‐TEM were utilized to analyze the mechanical properties and microstructure of the fiber. After oxidation in dry air and Ar–H2O–O2 for 1 h, respectively, the fiber strength retention rate has been found to decrease with the increased oxidation temperature. The raise in oxidation temperature also led to the increase of the thickness and the crystallization rate of the oxide scale. The most different oxidation behaviors of SiC being treated under the simulated environment than in air are the lower oxidation activation energy and the higher crystallization activation energy for cristobalite. Water vapor can promote the oxidation reaction and inhibit the crystallization of cristobalite in the oxide scale. Few significant differences have been observed otherwise in the oxidation process and oxidation chromatography crystallization mechanism of fibers being treated under different conditions. The increase of oxide layer thickness and the formation of cristobalite impair the structural integrity and compactness of the oxide scale and thus lead to the deterioration of the mechanical properties of SiC fibers. Therefore, it is proposed that oxidation resistance of SiC fiber can be improved by insulating the reaction between the oxidizing agents and the SiC fiber or by increasing the crystallization temperature of cristobalite in the oxidation process and reducing the crystallization rate. [ABSTRACT FROM AUTHOR]

Polymer-derived SiC fibers are critical structural and functional materials for high-temperature applications, whose service performance can be further improved by introduction of certain heterogeneous elements. Herein, flexible and thermal stable SiC fiber mats were prepared from boron-doped polyaluminocarbosilane (PACS) precursor by electro-spinning, curing and pyrolysis. Two boron-containing compounds o-carborane (oCB) and phenylboronic acid (PBA) were used as the boron sources and their effects on the properties and structure of the SiC fiber mats were investigated. The introduced oCB and PBA had obviously improved the ceramic yield of the cured fiber mats and the flexibility of the SiC fiber mats. However, PBA introduced more boron, but also more oxygen, which leaded to formation of more amorphous SiC x O y phases. Although only a small amount of boron was introduced by oCB, a more significant improvement in the thermal stability of the SiC fiber mat was obtained. This work provided a practical approach for fabrication of flexible and thermally stable SiC fiber mats. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The performance of continuous SiC fiber-reinforced titanium matrix composites (SiC f /Ti) is highly dependent on the interfacial reaction layer (RL) and the microstructure of the matrix. In this study, SiC f /Ti 2 AlNb precursor wires were fabricated using magnetron sputtering, and SiC f /Ti 2 AlNb composites were produced via hot isostatic pressing (HIP). The study explored the interfacial reactions and matrix microstructure evolution induced by HIP. It was found that the precursor wires interface mainly consisted of a TiC layer with an average thickness of 43.31 ± 8.17 nm, while the matrix exhibited a uniform elemental distribution and a complex nano-scale structure composed of O, B2, and α 2 phases. After HIP, elemental diffusion occurred at the interface, forming a multilayer structure that included fine-grained TiC, coarse-grained TiC, and α 2 layers, with thicknesses of 53.79 ± 12.03 nm, 0.46 ± 0.03 μm, and 0.45 ± 0.05 μm, respectively. The matrix evolved into a micron-scale O+B2+α 2 phase structure, with lath-O phase precipitates observed in the B2 phase. The enrichment of matrix elements was attributed to self-diffusion of matrix elements (leading to the formation of a micron-scale phase structure). These findings provide valuable insights into the structural transformation and interfacial evolution of SiC f /Ti 2 AlNb composites under HIP conditions. • The interfacial reaction product in the precursor wires is fine-grained TiC. • The interfacial reaction product in the composites is fine-grained TiC, coarse-grained TiC, and α 2. • During the HIP, the nano-scale α 2 +B2+O in the precursor wires matrix transforms into micro-scale α 2 +B2+O in the composites. • The HIP affects the element distribution and interfacial reaction layer in the SiC f /Ti 2 AlNb composites. [ABSTRACT FROM AUTHOR]

The degradation of SiCxOy phase is a crucial step during the conversion of polyaluminocarbosilane-derived amorphous Si-Al-C-O fiber into highly crystalline SiC fiber. In this work, the high-temperature degradation process of SiCxOy phase of Si-Al-C-O fiber was directly investigated by TG-MS analysis. Two distinct degradation behaviors were observed in the open and closed systems, and three oxygen-containing gaseous products, namely, CO, SiO and monoatomic O, were detected during the degradation process. Oxygen was found to act as a necessary initiator and accelerant of the degradation reaction of SiCxOy phase. A possible mechanism was proposed for the degradation reaction of SiCxOy phase based on the TG-MS results. Si-Al-C-O fiber was heat-treated under CO-filled Ar atmosphere in open and closed systems. Different effects of CO on the degradation reaction of SiCxOy phase in the two systems were observed and reasonably explained by the mechanism. [ABSTRACT FROM AUTHOR]

Continuous SiC fibers were used to toughen tungsten in this work. The composites were prepared by hot-press using W powders sintered from 1500°C to 1900°C for 1 h with 20 MPa pressure. Phases changes, microstructure, mechanical and thermal properties of composites were examined. Besides, the kinetics between SiC and W was also studied. The stress-strain curve had pseudo-ductility at room temperature, except for 1900°C sintered samples due to complete damage of fiber. Thermal conductivity was calculated from two directions: in-plane and throughplane directions (parallel and vertical to fiber direction), in which through-plane direction display higher thermal conductivity than other direction. Besides, severe reaction was verified between SiC and W, and the reaction rate increased 18 times when temperature increased from 1500°C to 1700°C. Therefore, it is suitable to use SiC fiber to reinforce W to ameliorate the brittleness with limited reaction between fiber and matrix. [ABSTRACT FROM AUTHOR]

As an important load-bearing part of SiCf / SiC composites, the microstructure and performance evolution of SiC fibers under high temperature oxidative environment directly affect their practical application. This paper reviewed the oxidation mechanism and oxidation model, as well as the influencing factors of oxidation behavior of SiC fibers. The approaches to improve the oxidation resistance of SiC fibers were also summarized and introduced. The oxidation behavior of SiC fibers is divided into passive and active oxidation according to the oxygen partial pressure. The high temperature oxidation in the water-oxygen environment accelerates the increase of the SiC fibers oxide layer thickness and the generation of cracks, resulting in the degradation of the mechanical properties. The composition and microstructure also have different effects on the oxidation results. This paper is intended to provide some reference for the application of SiC fibers under high temperature oxidative environments. [ABSTRACT FROM AUTHOR]

Y 3 Si 2 C 2 ternary ceramics were in-situ grown on the third-generation Chinese commercial SiC fiber (KD-SA SiC fiber) surface via molten salt method. Microstructures and oxidation/corrosion behavior of in-situ grown Y 3 Si 2 C 2 coated SiC fibers exposed to air and wet-oxygen at 1400 ℃ were investigated. Results indicated that the layered Y 3 Si 2 C 2 slices with thickness of approximately 15 nm can be successfully in-situ grown on SiC fibers. The product on the fibers surface after oxidation/corrosion at 1400 ℃ for 1 h in both ambient air and wet-oxygen are Y 2 Si 2 O 7 and SiO 2. Moreover, microstructural characterization indicates that the immigration and expansion of gaseous bubbles induced by oxidation product, mainly CO, result in microstructural differences of SiC fiber specimens, and finally oxidation mechanism based on the microstructural difference were proposed. [ABSTRACT FROM AUTHOR]

The mechanical behavior of silicon carbide (SiC) fiber used in ceramic matrix composites is valuable to permit the prediction of composite behavior and tailoring of composite properties. Herein, single‐fiber tensile tests of different SiC fibers are carried out and Weibull analysis is implemented to characterize its tensile property. To better understand its mechanical behavior, the surface and tensile fracture morphology of different fibers are observed by scanning electron microscopy (SEM) and the fiber elemental composition along the radial distribution is qualitatively analyzed by energy dispersive spectrometer (EDS). Also, the crystallinity and crystallite size of the fiber are analyzed by X‐ray diffraction (XRD). The results show that the tensile strength of SiC fiber conforms to the Weibull distribution, and its mechanical property is influenced by the surface morphology, elemental composition, crystallinity, and crystallite size. [ABSTRACT FROM AUTHOR]

Although SiC fibers are promising reinforcement materials for applications in high-temperature environments, the effects of heating on the thermomechanical and thermoelectrical properties of these fibers have not been discussed and correlated with the associated microstructural changes. To bridge this gap, we herein in situ monitored the elastic modulus and electrical conductivity changes accompanying the conversion of single amorphous Si–Al–C–O fibers to Si–Al–C polycrystalline fibers during heating to up to 1900 °C in vacuum using an in-house-built device. The weight and tensile strength changes due to heating at 1200–1900 °C in vacuum were correlated with the concomitant fiber crystallinity and microstructural changes. The mechanical and electrical properties of the fibers were related to the porous structure formed by the decomposition of the amorphous SiC x O y phase, rigid structure bonded by nanograin sintering–induced grain growth, and carbon layer formed by Si sublimation from the fiber surface. • Thermal conversion of amorphous Si–Al–C–O (AM) fibers to Si–Al–C polycrystalline fibers evaluated. • Monitoring of thermomechanical and thermoelectrical property degradation of the AM fibers measured at up to 1900 °C. • Weight and tensile strength changes correlated with the concomitant fiber crystallinity and microstructural changes. • Enhanced tensile strength at heating at 1900 °C due to transition from porous to rigid structure. [ABSTRACT FROM AUTHOR]

• Novel method is applied to fabricate SiC fiber-reinforced Al matrix composites. • SiC fibers with high volume fraction is introduced into the Al matrix uniformly. • SiC fiber significantly improve the mechanical properties of Al matrix composites. • Coefficient of thermal expansion decreases with increasing the SiC fibers' content. Combining the colloidal dispersion method with the squeeze melt infiltration technique, aluminum matrix composites with different volume fractions of silicon carbide fiber were fabricated at 680 °C under vacuum. Microstructure analysis found that composite presented a dense structure and fibers were homogeneously distributed in matrix. The hardness, yield strength and elastic modulus of the composite monotonically increased with increasing the volume fraction of fiber. The highest flexural strength for composite with 10 vol% SiC fiber was achieved. The improved mechanical properties could be attributed to the dispersion strengthening and enhanced load transferring ability by fibers as well as the dislocation strengthening. On the other hand, the coefficient of thermal expansion of composites was measured at temperature up to 400 °C. It was found that the uniform introduction of silicon carbide fiber could significantly low the CTE of aluminum matrix composite, which could be attributed to the low CTE of SiC fiber and good fiber–matrix interface bonding. [ABSTRACT FROM AUTHOR]

• Multifilament test results almost correspond to monofilament test results. • Fiber diameter variation does not affect multifilament test results considerably. • Diameter variation along gauge length may affect multifilament test result. The tensile strength distributions of five types of silicon carbide (SiC) fiber, namely, Nicalon, Hi-Nicalon, Hi-Nicalon TypeS, Tyranno ZMI and Tyranno SA, were evaluated by monofilament and multifilament tow tensile testing with the estimated Weibull parameters being compared from each method. Whereas values for the Weibull scale parameter were found to be similar for both the monofilament and multifilament test methods, the Weibull shape parameter obtained from multifilament tow testing tended to be greater than that obtained from monofilament testing. The effect of diameter variation within individual fibers on the multifilament tow test results was investigated by Monte-Carlo simulations. In contrast with the experimentally obtained results, the shape parameters calculated by Monte-Carlo simulation exhibited good agreement with the monofilament test results. [ABSTRACT FROM AUTHOR]

Flexible ultrafine SiC fibers with superior high-temperature stability and excellent oxidation resistance are regarded as one of the most promising materials for high-temperature applications. However, excess oxygen and carbon in the ultrafine SiC fibers limit their thermal stability due to decomposition of the SiC x O y phase. In the present work, flexible ultrafine nearly stoichiometric polycrystalline SiC fibers were fabricated by combining the electrospinning technique and polymer-derived ceramic method. The ultrafine SiC fibers exhibited superior high-temperature stability and oxidation resistance. The retention rates of tensile strength were 90.0 %, 94.2 % and 86.4 % after heat treatment in argon at 1800 °C, 1900 °C and 2000 °C, respectively. TG results of the fibers showed little weight loss of only 1.52 % at 1900 °C in Ar and the weight gain of only 4.1 % up to 1500 °C in air. Such improved thermal stability was achieved through sintering at high temperature for elimination of excess oxygen and carbon with Al doped as the sintering aid to restrain the grain coarsening. The ultrafine SiC fibers still exhibited excellent flexibility without obvious damage when they were heated by the butane blowtorch flame of about 1100 °C in air. Furthermore, the infrared thermography illustrated that the ultrafine SiC fiber membrane also had good thermal insulation performance. The outstanding mechanical properties and thermal stability of ultrafine SiC fibers suggest their potential applications at the high temperature and harsh environment. [ABSTRACT FROM AUTHOR]

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In this study, PyC coating with different thickness was prepared on SiC fibers via chemical vapor deposition method. Uncoated and PyC coated SiC fibers were heat treated in Ar atmosphere under different annealing condition. The effects of PyC coating on the mechanical properties of SiC fibers at room temperature were investigated. The morphology, composition, structure and mechanical properties of SiC fibers after high temperature treatment were also studied. The results showed that PyC coating could reduce the dispersion of tensile strength for SiC fibers. Weibull modulus increased from 4.19 (SiC fiber) to 5.59 (PyC700 fiber), while the tensile strength decreased a little with the increment of PyC coating thickness. Furthermore, PyC coating could remarkably retard Si sublimation from SiC fiber at high temperature. Uncoated SiC fiber was converted to porous pure-carbon fiber after being annealed at 2000 °C for 5 h, while PyC700 fiber still showed relative dense SiC core after the same treatment. To a certain extent, the inhibition ability was improved with increment of PyC coating thickness. In addition, PyC coated SiC fibers could maintain more tensile strength after being annealed at 1800 °C for 1 h. The tensile strength retention of uncoated SiC fiber was 27.3%, while that of PyC700 fiber could reach up to 43.2%. [ABSTRACT FROM AUTHOR]

A novel ternary layered ceramic of Y 3 Si 2 C 2 was successfully in-situ synthesized on the surface of home-made third-generation KD-SA SiC fiber for the first time by molten salt method aimed at improving the electromagnetic wave (EMW) absorption. After in-situ synthesis of Y 3 Si 2 C 2 ceramic layer on SiC fiber (SiC f /Y 3 Si 2 C 2), significantly improved EMW absorption performance was obtained. The minimum reflection loss (RL min) of −16.97 dB was reached in SiC f /Y 3 Si 2 C 2 composites at the thickness of only 2.19 mm, and the effective absorption bandwidth (EAB) was up to 5.44 GHz (12.56–18 GHz) at a thin thickness of 2.64 mm. The improvement in EMW absorption of SiC f /Y 3 Si 2 C 2 is mainly attributed to enhanced dielectric loss and conduction loss resulting from increased heterogeneous interfaces and multiple reflections and scattering originating from net structure. The SiC f /Y 3 Si 2 C 2 could be a promising EMW absorber for application in high-performance EMW absorbing materials. [ABSTRACT FROM AUTHOR]

In this study, the amorphous C, ZrB2, and BN single‐layer coatings as well as C/BN, C/ZrB2, ZrB2/BN, and C/ZrB2/BN composite coatings were prepared on SiC fibers (SiCf) by an in situ synthesis and solution impregnation–pyrolysis method. Subsequently, SiCf/SiBCN composites were fabricated by hot‐pressing sintering at 1900℃/60 MPa/30 min to explore the influence of different coatings on the microstructure and mechanical performance of resulting composites. After the preparation of single‐layer‐coated SiCf, the SiCf(BN) or SiCf(ZrB2) tended to be overlapped with each other, whereas the dispersion of amorphous C–coated SiCf was satisfying. Besides, some uneven areas and attached particles have appeared on fiber surfaces of the SiCf(BN) or SiCf(ZrB2), whereas smooth and dense surfaces of amorphous C–coated SiCf were observed. Because the uniformity of ZrB2 coatings can be partially damaged by the subsequent coating process of BN, the composite coatings of ZrB2/BN and C/ZrB2/BN were thereby not suitable for strengthening SiBCN matrix. The SiCf/SiBCN composites with C/ZrB2 coatings have desirable comprehensive mechanical properties. Nevertheless, the conventional toughening mechanisms such as fiber pull‐out and bridging, and crack deflection are not available for these composites because the serious crystallization of SiCf leading to great strength loss, resulting in catastrophic brittle fracture. [ABSTRACT FROM AUTHOR]

Slow crack growth parameters for SiC-based filaments. τ is the lifetime, σ app the stress, n f the stress exponent and Ea τ the apparent activation energy describing the Arrhenius evolution of the environment constant A with temperature. [Display omitted] • Modified time to failure prediction expression applied to various SiC-based fibers. • Stress exponent subjected to a scale effect, induced by fiber misalignment. • Estimates for SCG parameters of SiC-based filaments. • Stress-probability time diagrams construction from simulation output. • Correlation between stress exponent and chemical composition (O and H content). The delayed failure of SiC fibrous reinforcement has continuously been investigated to warrant the long term performances of Ceramic Matrix Composite (CMC). Chiefly assessed on multifilament tow samples to alleviate some handling difficulties, subcritical crack growth (SCG) parameters are however ruled by structural artifacts which hinder the identification of intrinsic filament behavior. In this paper, we propose to estimate the true filament parameters for 5 fiber types from bundle behavior using a recently communicated Monte Carlo algorithm integrating flaw and stress distributions through a deterministic fracture mechanics law under Paris' formulation. So computed tow lifetime are broadly dispersed, encompassing raw data, and show a structure-dependent scale effect, revealed by n filament >n tow where n is the stress exponent. The relationship between SCG coefficient and chemical composition of the substrate is discussed and highlights the major effect of doping elements (Ti or Zr), oxygen or hydrogen content. [ABSTRACT FROM AUTHOR]

The sensitivity of strength via temperature for SiC/SiC composites and SiC fibers in an oxygen-free environment is studied through experimental investigation and theoretical analysis. Tensile tests are performed on SiC/SiC minicomposites at room temperature, 500 and 1000 ℃ in an oxygen-free environment. A high-efficiency method is proposed to obtain the high-temperature strength distribution of SiC fibers. The experimental results show that the sensitivity of strength via temperature is high for SiC fibers but low for SiC/SiC minicomposites. To explain this phenomenon, the strength model of minicomposites is developed. The theoretical analysis reveals that the low sensitivity of strength via temperature for minicomposites results from that the influences of the changes of the Weibull parameters m and σ0 at elevated temperatures are offset. [ABSTRACT FROM AUTHOR]

SiC fibers have been widely investigated as reinforcements for advanced ceramic matrix composites owing to their excellent high‐temperature properties. However, the axial compressive strength of SiC fibers has not been thoroughly studied. In this study, the compressive behavior of two SiC fiber types containing different compositions and thermal degradation were characterized by tensile recoil measurements. Results illustrated that the SiC fiber compressive strength was 30%–50% of its tensile strength, after heat treatment at 1200℃–1800℃ for 0.5 h in argon. The fiber compressive failure mechanism was studied, and a "shear‐bending‐cleavage" model was proposed for the recoil compression fracture of pristine SiC fibers. The average compressive and tensile strengths of the pristine SiC‐II fiber were 1.37 and 3.08 GPa, respectively. After treatment at 1800℃ for 0.5 h in argon, the SiC‐II fiber compressive strength decreased to 0.42 GPa, whereas the tensile strength reduced to 1.47 GPa. The mechanical properties of the fibers degraded after high‐temperature treatment. This could be attributed to SiC grain coarsening and SiCxOy phase decomposition. [ABSTRACT FROM AUTHOR]

A new approach to improving the interfacial compatibility of SiCf/Ti-6Al-4V composites by using fiber coating coupled with subsequent heat treatment was presented. The SiCf/Ti-6Al-4V composites with C-coated and C/Mo-coated fibers were prepared using the foil-fiber-foil method and subsequently heat treated in vacuum at 750 °C to obtain several kinds of the SiCf/Ti-6Al-4V composites with different interfacial characteristics. Interfacial microstructures of these composites were systematically characterized by means of scanning electron microscopy and X-ray energy dispersive spectroscopy to investigate the interfacial microstructure evolution and reaction dynamics. The effects of interfacial microstructures on interfacial mechanical properties were also investigated using thin-slice fiber push-out tests. The results show that the brittle interfacial reaction layer of TiC in the C-coated SiCf/Ti-6Al-4V composites was obviously thickened and some microvoids even formed near the matrix with increasing heat treatment durations, whereas the matrix adjacent to Mo coating in the C/Mo-coated SiCf/Ti-6Al-4V composites gradually transformed into a ductile β-Ti layer. Interfacial shear strengths of the C/Mo-coated composites were slightly increased with increasing the heat treatment time, while those of the C-coated composites were remarkably improved. Critical issues on modifying interfacial compatibility of the SiCf/Ti composites for further improving the mechanical behavior of the composites were discussed.

SiC fiber reinforced SiC matrix composites (SiC/SiC composites) are a kind of ceramic matrix composites (CMC) and have attracted attention as a new material for aerospace engines because of their high strength, high temperature resistance, and oxidation resistance. The dry-spinning method for SiC fibers is one of approach to reduce the fabrication cost of SiC/SiC composites. In the dry-spinning method, the raw material, polycarbosilane (PCS) is dissolved in a volatile solvent and spun. This method can skip the curing process, which is the cause of high cost. In this study, dry-spun SiC fibers were fabricated by changing molecular weight of PCS and heat-treatment temperature. The mechanical properties of SiC fibers were determined by monofilament tensile tests. The highest tensile strength and elastic modulus of the dry-spun SiC fibers were 2.88 GPa and 270 GPa, respectively. These mechanical properties strongly effected the molecular weight of PCS, the heat-treatment temperature, and the fiber diameter. As the molecular weight of PCS was higher than a certain threshold, the excessive crystallization was observed causing the decrease of mechanical properties. In addition, the defects inside the fiber increase when molecular weight is higher. The heat-treatment temperature also affected the crystallization and the increase of defects with depending on the molecular weight of PCS. The crystal size enlarged with increasing the heat-treatment temperature, while the fracture morphology remained unchanged.

The SiC fibers were coated with Ti 3 SiC 2 interphase by dip-coating. The Ti 3 SiC 2 coated fibers were heat-treated from 900 °C to 1100 °C in vacuum and argon atmospheres to comparatively analyze the effect of temperature and atmosphere on the microstructural evolution and mechanical strength of the fibers. The results show that the surface morphology of Ti 3 SiC 2 coating is rough in vacuum and Ti 3 SiC 2 is decomposed at 1100 °C. However, in argon atmosphere, the surface morphology is smooth and Ti 3 SiC 2 is oxidized at 1000 °C and 1100 °C. At 1100 °C, Ti 3 SiC 2 oxidized to form a thin layer of amorphous SiO 2 embedded with TiO 2 grains. Meanwhile, defects and pores appeared in the interphase scale. As a result, the fiber strength treated in the argon was lower than that treated in vacuum. The porous Ti 3 SiC 2 interphase fabricated under vacuum was then employed to prepare the SiC f /SiC mini composite by chemical vapor infiltration (CVI) combined with precursor infiltration pyrolysis (PIP), and can effectively improve the toughness of SiC f /SiC mini composite. The propagating cracks can be deflected within the porous interphase layer, which promotes fiber pull-outs under the tensile strength. [ABSTRACT FROM AUTHOR]

An electromagnetic wave absorbing material acting from 8.2 to 12.4 GHz (X-band) is fabricated by mixing BN-coated SiC fiber with AlPO4 matrix, and using multiwalled carbon nanotubes (MWNCTs) as the absorber. The effect of temperature on the microstructure of BN interface is disclosed by XRD and FT-IR characterizations. The crystallinity of BN increased with elevated temperature. The fracture strength of SiCf/BN/AlPO4 composites rise from 175 to 350 MPa and the fracture displacement was elevated from 0.25 to 0.7 mm. The increasing complex permittivity of SiCf/BN/AlPO4/MWCNTs composites in the temperature range of 25–600 °C is ascribed to the shortened electron polarization-relaxation time and improved electrical conductivity. Attenuation constant and input impedance are chosen to discuss the reflection loss of the composites. Finally, a 4.2 GHz absorbing bandwidth below −8 dB is achieved with 3.1 mm thickness in the range of 25–600 °C. [ABSTRACT FROM AUTHOR]