Silicon Carbide Fibers Research Articles

Study on the Grooved Morphology of CMC-SiCf/SiC by Dual-Beam Coupling Nanosecond Laser

Due to the excellent properties of high hardness, oxidation resistance, and high-temperature resistance, silicon carbide fiber reinforced silicon carbide ceramic matrix composite (CMC-SiCf/SiC) is a typical difficult-to-process material. In this paper, according to the relationship between the spatial posture of dual beams and the direction of the machining path, two kinds of scanning methods were set up. The CMC-SiCf/SiC grooving experiments were carried out along different feeding directions (transverse scanning and longitudinal scanning) by using a novel dual-beam coupling nanosecond laser, and the characteristics of grooving morphology were observed by Laser Confocal Microscope, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometer (EDS). The results show that the transverse scanning grooving section morphology is V shape, and the longitudinal scanning groove section morphology is W shape. The grooving surface depth and width of transverse scanning are larger and smaller than that of longitudinal scanning when the laser parameters are the same. The depth of the transverse grooving is greater than that of the longitudinal grooving when the laser beam is transverse and longitudinal scanning, the maximum grooving depth is approximately 145.39 μm when the laser energy density is 76.73 J/cm2, and the minimum grooving depth is approximately 83.76 μm when the laser energy density is about 29.59 J/cm2. The thermal conductivity of fiber has a significant effect on the local characteristics of the grooved morphology when using a medium energy density grooving. The obvious recasting layer is produced after the laser is applied to CMC-SiCf/SiC when using a high energy density laser grooving, which directly affects the grooved morphology.

New insights on the ablation mechanism of silicon carbide in dissociated air plasmas

Thermal protection system (TPS) applied in space vehicle is mainly composed of silicon carbide (SiC) and related components. When exposed in re-entry flows, the SiC based TPS may suffer from severe ablation if the surface temperature is beyond a critical threshold (generally ≥1600°C). Unveiling the ablation mechanism of SiC is thus vitally important to define the borders of service and to help optimize the TPS structures in re-entry environments. Motivated by this, this work uses an inductively coupled plasma wind tunnel to generate the dissociated air plasmas and explores the ablation behaviors of several SiC materials (including SiC ceramic and SiC fiber reinforced SiC matrix composites). Some new insights are acquired based on the detailed analysis of the surface characteristics prior to and after ablations. First, the role of surface roughness on the critical ablation temperature of the SiC based composite is put forward. Second, a ‘from-point-to-surface’ ablation process due to the surface roughness during the short ‘temperature jump’ is proposed, which is an important supplementary to the existing ablation model of SiC; Finally, a smoother surface with less defects is concluded to efficiently enhance the ablation resistance of the SiC based TPS in re-entry environments.

Research on the ablation mechanism and ablation threshold of CMC-SiCf/SiC by using dual-beam coupling nanosecond laser

Due to the excellent properties of high hardness, oxidation resistance and high temperature resistance, silicon carbide fiber silicon carbide ceramic matrix composite (CMC-SiC f /SiC) is a typical difficult-to-process material, and is a high-performance advanced material in the aerospace field. In this paper, two groups of ablation experiments (experiment 1 and experiment 2) were performed on CMC-SiC f /SiC using a dual-beam coupling nanosecond laser, and the ablation morphology was observed by confocal laser microscope. The dual-beam coupling angle of experiment 2 is obtained by experimental method. And through the method of calculation, we get the dual-beam coupling angle of experiment 1 and experiment 2. According to the dual-beam coupling ablation mechanism, based on the theoretical calculation model of non-destructive method D 2 -ln P 0 , combined with the Equivalent Diameter Calculation Method (EDCM) and Equivalent Area Calculation Method (EACM), the laser ablation threshold corresponding to different beam waist size was calculated and compared. The results show that the ablation region of CMC-SiC f /SiC surface can be divided into three parts: ablation boundary, recast layer area and SiO 2 coverage area. When the pulse energy increases gradually from 300 μJ to 1500 μJ, the variation trend of hole depth is first increase, second decrease, increase again, and finally decrease. The angle between two laser beams affects the waist radius, which in turn affect the laser ablation threshold. The waist of the dual-beam coupling is elliptical, and the orifice of the ablation hole is elliptical. When the waist radius of nanosecond laser is 57 μm, the laser ablation threshold is calculated to be 3.12 J/cm 2 . The main factors affecting the laser ablation threshold are laser pulse repetition frequency ( f ), beam waist radius ( ω 0 ), laser pulse width ( τ ), minimum laser power ( P th ), and laser wavelength ( λ ).

Current research art of rare earth compound modified SiC-CMCs for enhanced wet-oxygen corrosion resistance

Silicon carbide fiber reinforced silicon carbide ceramic matrix composites (SiC-CMCs) currently present wide application potential as thermal structure component in aero-engine. To solve the wet-oxygen corrosion induced degradation of SiC-CMCs attract growing global attention. In this work, the main preparation methods via introduction of rare earth compound like rare earth phosphates, rare earth oxides, rare earth silicates and rare earth silicide carbides into SiC-CMCs matrix and interphase and their microstructures, mechanical properties and wet-oxygen corrosion resistance are summarized in details. Finally, the challenges and prospects of rare earth compound modified SiC-CMCs are proposed.

Mechanical modeling of ultrasonic vibration helical grinding of SiCf/SiC composites

To reveal the mechanical characteristics of silicon carbide fiber reinforced silicon carbide ceramic matrix (SiCf/SiC) composites during the hole-making process, a mechanical model was developed and a hole-making experiment of ultrasonic vibration helical grinding (UVHG) was conducted to validate the mechanical model. To establish the model, the kinematic simulation of a single grain was carried out, which providing a theoretical basis for the selection of experimental parameters. Based on the kinematic simulation of the single grain, the contact behavior between the single grain and material was analyzed. The mechanical model considered comprehensively the force of fiber fracture, the force of matrix cracking, the force of interface wear, the force of friction, and the force of ultrasonic vibration. The results indicated that the maximum error percentage between the predicted value and the experimental value of the mechanical model is 21.1%. The high ultrasonic amplitude can effectively decrease the grinding force, as well as a low helical feed rate and a low pitch within the range of experimental parameters.

Microstructure and mechanical properties of SiCf/SiC composite prepared by chemical vapor infiltration

Continuous silicon carbide (SiC) fiber reinforced SiC ceramic matrix (SiCf/SiC) composites are widely studied for possible applications as hot sections in next-generation aeroengines because of their excellent thermo-structural properties. Their mechanical properties were comprehensively evaluated based on the interaction mechanisms among fiber, interphase, and matrix. Moreover, it was found that matrix cracking and fiber bridging mechanisms influenced the shear-dominated and tension-dominated properties, respectively, clearly indicating that the mechanical properties of the material should be correlated. In this study, mechanical properties of the two-dimensional SiCf/SiC composite were comprehensively evaluated, and the correlation laws were verified between tension and bending, tension and in-plane shear, and in-plane shear and interlaminar shear. Results showed that the ratio of shear to tensile matrix cracking stress was 0.68, while the ratio of flexural to tensile strength was 2.3, and the interlaminar shear strength was equal to the in-plane shear strength minus the fiber bridging stress. Fiber bridging is the key mechanism controlling the above-mentioned correlation by the established meso-mechanical formulas, and the interlaminar shear mechanism is controlled by matrix cracking and influenced by interlaminar pores.

Properties of super heat-resistant silicon carbide fibres with in situ BN coating

An in situ BN coating was prepared on the surface of a nearly stoichiometric continuous SiC fibre with trademark Cansas-3301 (C3). The coated fibre was then subjected to continuous pyrolysis at 1800 °C, obtaining a fibre named Cansas-BN-1800 (C18). After annealing in Ar at 1500 °C for 1 h, the strength retention ratio of C3 was 49%, and that of C18 was almost unchanged. The strength decrease of the C3 fibre was mainly caused by the formation of surface defects resulting from fibre decomposition and active oxidation. However, the in situ BN coating on C18 protected the fibre from forming surface defects, resulting in high strength. Due to slight growth of the grain and purification of the grain boundary during fast heating at 1800 °C, C18 showed excellent creep resistance in the range of 1200–1500 °C.

Improving the mechanical properties of amorphous silicon carbide fibers by forming a protective silicon dioxide layer

Silicon carbide fiber is a representative structural material that has been studied as a major reinforcement material for ceramic matrix composites (CMCs). SiC fibers are classified by their operating temperature, manufacture process, composition, and crystallinity. Among the various SiC fibers, amorphous ones are composed of a Si–O–C amorphous matrix and nanoscale SiC crystals, and amorphous fibers exhibit amorphous fracture behavior. An amorphous fiber is almost always fractured by surface flaws generated during the manufacturing process. In this study, we aimed to strengthen the surface by etching the surface cracks and forming a SiO2 oxidation layer, and then evaluated the effect of the oxide layer thickness on the fracture behavior and control of surface defects. The passive oxidation layer was formed by exposing the fiber bundles to air atmosphere at a temperature higher than 1000 °C. The mechanical properties of the strengthened fibers were evaluated through single-filament tensile strength tests, and the fracture distribution was analyzed using Weibull distribution. Further, fractographic analyses were conducted on the cross-sectional microstructures observed by field-emission scanning electron microscopy. The surface-oxidized fibers exhibited enhanced flexibility owing to the crack-blunting effect of the SiO2 layer.

Experimental investigation of morphological and mechanical properties of SiC-neem-coir fiber reinforced hybrid composite

ABSTRACT The present work is the novel investigation of a hand layup fabricated hybrid epoxy matrix composite with silicon carbide and neem-coir natural fibers as primary and secondary reinforcements respectively. The hybrid composites were fabricated at varying volume fractions of reinforcements to determine the influence of reinforcements composition on the physical performance of the resulting composite. The fabricated hybrid composites were characterized for mechanical behaviour by tensile and hardness tests. The fiber-matrix interfacial layer was examined by microscopy for morphological behaviour, and the composition was examined by energy dispersive X-ray analysis. The analysis revealed that among the three fabricated composite combinations, the hybrid epoxy matrix SiC-neem-coir reinforcement composite exhibited the peak tensile strength of 53 MPa and the Shore D hardness of 78.1. Enhancement in flexural strength was obtained for the hybrid composite with natural fiber volume fractions of 6% and 3% for neem and coir respectively. The morphological analysis revealed that silicon carbide as primary reinforcement was effective in improving mechanical properties of the composite, but with inconsistent property enhancements. The addition of neem-coir as secondary reinforcements in varying compositions exhibited bolstering effects on the mechanical properties of the composite and maintaining consistency of enhancement over various composition samples.

Mechanical property of Pyro-Carbon coated SiC fibers fabricated by continuous chemical vapor deposition method

PurposeA continuous chemical vapor deposition (CVD) method has been used to fabricate pyro-carbon (PyC) coating on continuous silicon carbide (SiC) fibers. The paper aims to evaluate these coated fibers by testing filament tensile and using microstructure characterization.Design/methodology/approachThe continuous SiC fiber-reinforced SiC matrix (SiC/SiC) composite is widely studied in aerospace and nuclear applications. The PyC is the probable option in fusion and fast reactor. However, the conventional fabrication method of PyC coating has some drawbacks influencing performance and efficiency.FindingsThe results showed that PyC-coated SiC fibers with continuous CVD method are more straight than conventional ones and residual deformations could not be observed, and these PyC coatings have complete geometry and uniform thickness. In different process conditions, the thickness of PyC coating could control from ∼100 to ∼1,000 nm.Originality/valueThe coated SiC fibers in a lower gas ratio (1:7 to 1:3), lower pressure (500–1,000 Pa) and appropriate winding speed (3 to 5 rpm) have relative high filament tensile strength (∼3.5 to ∼3.9 GPa). And the strength of coated SiC fibers has a negative correlation with the measured thickness of PyC coating. A distinctive growth process was discovered in the continuous CVD method. In a certain range, the quicker growing rate of PyC is obtained in shorter deposition time which means an efficient and quality method could be applied to fabricate coatings.

Quantitative atomic force microscopy: A statistical treatment of high-speed AFM data for quality control applications

Prior to the recent developments of high-speed atomic force microscopy (HS-AFM), atomic force microscopy (AFM) was not favoured by industry because of its complexity and slow image acquisition speed which may lead to poor resolution and unreliable quantified results. HS-AFM, however, is capable of imaging several frames per second and thus capable of quick, accurate, and representative measurements – ideal for quality control applications. This study demonstrates HS-AFM as a useful quality control tool by assessing the roughness of silicon carbide (SiC) monofilament fibres as a challenging example of how large HS-AFM datasets in excess of 200 images can be collected and used for reliable quantification.A comparison of two roughness methods utilising either area or line roughness parameters has been conducted, where very little difference was noted apart from the lower statistical significance of line roughness. The roughness of ten SiC fibre samples was measured with Sa (the area equivalent to Ra) roughness results varying from 34 nm to 53 nm. The small measurement uncertainties, as a result of the large number of measurements, meant that the roughness results were distinguishable from one another even though all ten SiC fibres were very similar to each other, having been produced by the same manufacturer and process. The robustness of the methods have been tested by repeating the analysis for each fibre, and in the one instance where the repeated data did not agree, a further dataset proved which one was incorrect, illustrating how industry can use these methods for quality control. A methodology of identifying the minimum number of frames required to account for sample variability, as well as recommendations on how to use HS-AFM for quantitative measurements in quality control, are also included to enable easy reproduction and adaptation of this work for other samples and measurements.

A novel pretreatment strategy for accurate determination the Al element content within polyaluminumcarbsilane

Polymer-derived silicon carbide (SiC) fibers show their merits of high-temperature resistance, oxidation resistance and corrosion resistance; and introducing certain amounts of hetero-elements into ceramic precursor could improve the properties of SiC fibers. Therefore, it is very important to accurately control the amount of introduced hetero-elements to optimize the functionalization of the target SiC fibers. The current method of hetero-element content determination in precursors is to directly adopt the method of hetero-element content in amorphous or microcrystalline ceramics. In contrast to ceramics, low molecule weight Al-contained precursors are easy to volatilize during the alkali fusion process. Moreover, the precursor digestion solution is more likely to produce silicic acid flocculent precipitation when the solution is treated after alkali fusion. These two main aspects seriously affect the detection accuracy of hetero-element content in precursors. In this work, taking polyaluminumcarbsilane (PACS), which is one of the most commonly used ceramic precursors, as a subject of research; and the effects of pretreatment conditions for accurate determination the Al element content within are investigated. The pretreatment method of air crosslinking for precursor, as well as pH value adjustment of digestion solution, is proposed; enabling the accurate detection of Al in PACS. The optimized pretreatment conditions are reached for obtaining the Al elements contents accordant with theoretical derived ones, showing that this method is accurate and reliable. This pretreatment strategy could be extended to other kinds of hetero-elements within precursors.

Feasibility of polarized laser scattering in detecting the grinding-induced subsurface damage in SiCf/SiC ceramic matrix composite

Given the urgent demand in the effective method for detecting the machining-induced damage (MID) of ceramic matrix composite (CMC). This study first time proposes the polarized laser scattering (PLS) method to detect the grinding-induced damage of silicon carbide fiber reinforced silicon carbide (SiCf/SiC). The feasibility of the PLS detection is demonstrated. Moreover, the sensitivity of PLS detection is found dependent on the radiation spot size of the laser beam. Decreasing the radiation spot size, the sensitivity to MID increases. However, the sensitivity to the pre-existed defects also increases, which would disturb the detection of MID. While increasing the radiation spot size, the intensity of the PLS detection decreases. In this study, when the radiation spot size is 66, 132, or 264 μm, the PLS method is suitable for detecting the grinding-induced damage of SiCf/SiC. This study is important for expanding the detection of the MID of CMC.

Oxidation Behavior of the Si-B-X (X = Mo, Cr, or Ti) Alloys in the Temperature Range of 1000-1400 °C.

Low-melting-point silicon–boron system alloys are promising for low-temperature reactive melt infiltration to reduce high-temperature damage to silicon carbide fibers during the densification of SiC/SiC composites. Meanwhile, the oxidation resistance of the alloys will have a large impact on the intrinsic oxidation resistance of the composite. Herein, three alloys, Si-14.88B-7Mo, Si-14.88B-7Ti, and Si-14.88B-7Cr, were fabricated to investigate the oxidation behavior in air at 1000–1400 °C. The results showed that the oxidation weight gains of the Si-B-Mo alloy after oxidation at 1400 °C for 100 h were 0.9 mg/cm–2, which were only 50 and 1.5% of those of Si-B-Ti and Si-B-Cr alloys, respectively. The excellent oxidation resistance of Si-B-Mo alloys at 1000–1400 °C was attributed to the formation of glassy-surface layers and the dense internal oxide layer. The dense oxide layer and the low solubility of Mo ions in SiO2 inhibit the volatilization of MoO3 and the oxidation reaction, reducing the oxidation rate of the Si-B-Mo alloy. The difference in the coefficients of thermal expansion for SiO2 and TiO2 led to penetrating cracks in the oxide layer of the Si-B-Ti alloy during cooling, thereby reducing the oxidation resistance. In addition, the rate of volatilization of Cr2O3 as CrO3 in an oxidation atmosphere above 1200 °C increased significantly in the Si-B-Cr alloy. The simultaneous volatilization of B2O3 and CrO3 resulted in the formation of loose oxide layers in the CrB2 region of the Si-B-Cr alloy, leading to severe oxidation.

Vertical carbon nanotubes arrays with controlled morphology on silicon carbide fibers for electromagnetic wave absorption

Silicon carbide fiber-Carbon nanotubes arrays (SiCf-CNTs) hybrids with controllable morphologies were successfully synthesized by a floating catalyst chemical vapor deposition method (CVD). As the reaction duration prolonged from 2 min to 15 min, the length of CNTs was elongated from 2 μm to 50 μm, and moreover the content of CNTs in the hybrids increased from 1.5 wt% to 3.7 wt%. By filling this chopped SiCf-CNTs (20 wt%) hybrids into paraffin, the composite with 3 mm in thickness presented the minimum reflection loss (RLmin = −56.2 dB) and the maximum effective absorption wideband (EAB, RL ≤ −10 dB) of 4.3 GHz (8.5–12.8 GHz). The dielectric performance of this hybrid synthesized by optimized CNT's length and growth density has presented high potential in the application of electromagnetic wave absorption.

Rare earth monosilicates as oxidation resistant interphase for SiCf/SiC CMC: Investigation of SiCf/Yb2SiO5 model composites

Model composites consisting of SiC fiber and Yb2SiO5 were processed by the spark plasma sintering (SPS) method. The mechanical compatibility and chemical stability between Yb2SiO5 and SiC fiber were studied to evaluate the potential application of Yb monosilicate as the interphase of silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiCf/SiC CMC). Two kinds of interfaces, namely mechanical and chemical bonding interfaces, were achieved by adjusting sintering temperature. SiCf/Yb2SiO5 interfaces prepared at 1450 and 1500 °C exhibit high interface strength and debond energy, which do not satisfy the crack deflection criteria based on He-Hutchison diagram. Raman spectrum analyzation indicates that the thermal expansion mismatch between Yb2SiO5 and SiC contributes to high compressive thermal stress at interface, and leads to high interfacial parameters. Amorphous layer at interface in model composite sintered at 1550 °C is related to the diffusion promoted by high temperature and DC electric filed during SPS. It is inspired that the interfacial parameters could be adjusted by introducing Yb2Si2O7−Yb2SiO5 interphase with controlled composition to optimize the mechanical fuse mechanism in SiCf/SiC CMC.

Tensile properties and failure mechanism of the SiCf/SiC minicomposite with multi-layered (BN/SiC)n interfacial coatings at room temperature

To overcome the brittle fracture of ceramic matrix composites, the interfacial coatings between continuous fibers and the ceramic matrix, especially boron nitride (BN) and silicon carbide (SiC) coatings were often introduced into the composites to improve the interface properties. This work focused on the use of chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) to fabricated SiC fiber-reinforced SiC (SiCf/SiC) minicomposites with interfacial coatings. Single BN, double-layered BN/SiC, and multi-layered (BN/SiC)2 interfacial coatings were deposited on SiC fibers from BCl3-NH3-H2 and MTS (Methyltrichlorosilane)-H2 systems in a low pressure hot-wall CVI reactor. Room-temperature tensile testing was used to evaluate the influence of different interfacial coatings on the tensile properties and failure mechanism of SiCf/SiC minicomposites. The minicomposites with (BN/SiC)2 coatings performed the highest fracture strength of 630.9 MPa. The mechanical behaviour of the composites was characterized by the universal testing machine with an acoustic emission (AE) detector, a scanning electron microscope (SEM), and an energy dispersive X-ray spectrometer (EDS). The existence of (BN/SiC)2 coatings provoked the interface debonding in the minicomposite both at the BN/fiber interface and the interface between BN and SiC layers, prolonging the crack propagation paths and noticeably improving the fracture properties of the minicomposite.

A Fast Thermal 1D Model to Study Aerospace Material Response Behaviors in Uncontrolled Atmospheric Entries.

A preliminary thermal 1D numerical model for studying the demise behavior of stainless steel 316L, silicon carbide (SiC) and carbon fiber reinforced polymer (CFRP) during uncontrolled atmospheric entry is proposed. Test case modeling results are compared to experimental data obtained in the framework of ESA Clean Space initiative: material samples were exposed to different heat flux conditions using the Plasma Wind Tunnel (PWT) facilities at the Institute of Space Systems (IRS) of the University of Stuttgart. This numerical model approximates the heating history of the selected materials by simulating their thermal response and temperature profiles, which have trends similar to the experimental curves that are found. Moreover, when high heat flux conditions are considered, the model simulates the materials’ mass loss due to the ablation process: at the end of the simulation, the difference between the experimental and the modeled results is about 17% for CFRP and 35% for stainless steel. To reduce the model’s uncertainties, the following analysis suggests the need to consider the influence of adequate material thermophysical properties and the physical-chemical processes that affect the samples’ temperature profile and mass loss.

Fabrication and high-temperature performance evaluation of silicon carbide – Hafnium carbide nanocomposite fiber

Silicon carbide fibers are used in silicon carbide fiber reinforced silicon carbide composite (SiCf/SiC) as reinforcement materials because of their outstanding mechanical properties, high-temperature durability and oxidation resistance. Owing to its excellent high-temperature performance, SiCf/SiC finds extensive application in materials exposed to extreme environments for long periods, such as nuclear fusion reactors, gas turbines, and rocket nozzles. Transition metal-based carbides, in particular hafnium carbide, have attracted considerable attention owing to their high melting point, high self-diffusion coefficient and chemical bonding energy. This study aims to improve the high-temperature creep characteristics of polycrystalline silicon carbide fibers by dispersing hafnium carbide nanocrystals in crystalline silicon carbide fibers and the changes in the microstructure, crystal phase and crystallite size were observed under various sintering conditions by different experiments. The results confirmed that hafnium carbide was uniformly dispersed, and that the crystal size grew to approximately 40 nm at a sintering temperature of 2000 °C. For high-temperature property evaluation, bend stress relaxation tests were conducted at temperatures in the range of 1000–1500 °C, and the effects of hafnium carbide were compared with those of other single silicon carbide fibers.

Fracture behaviour of SiC/SiC ceramic matrix composite at room temperature

Ceramic matrix composites are promising materials for structural applications at high temperature due to their excellent thermo-mechanical properties. Despite all their advantages, standardised methods for the characterisation of fracture toughness have not been established yet. Therefore, it is necessary to develop an understanding of their fracture behaviour. In this study, the fracture behaviour of silicon carbide (SiC) materials reinforced by SiC fibres is investigated using notched beams in flexural and tensile tests. The toughening mechanisms were identified. The work of fracture ranges between 4.0 and 24.6 kJ.m−2 and the fracture toughness KIC ranges between 3.2 and 5.5 MPa.m1/2. An equivalent fracture toughness Keq that reflects to some extent the degree of extrinsic toughening was defined and values range between 23.5 and 27.9 MPa.m1/2. KIC and the work of fracture decrease with increasing displacement rate while the strength was not affected. KIC measurements reveal the material’s anisotropy, higher values were obtained for the out-of-plane fibres orientation.