Silicon Carbide Ceramic Matrix Research Articles

Advancing SiC Coatings of Short‐Fiber Using Triethylsilane: Insights from FB‐CVD Deposition Process

AbstractThis study examines the use of triethylsilane (TES) as a non‐halogenated, less hazardous precursor in the Fluidized Bed ‐ Chemical Vapor Deposition (FB‐CVD) process for silicon carbide (SiC) coating on short fibers. It focuses on characterizing a pre‐matrix SiC layer over an interphase boron nitride (BN) coating, aiming to improve short‐fiber‐reinforced silicon carbide ceramic matrix composites (SiC/SiC CMCs). FB‐CVD is highlighted as a promising method for enhancing the applicability of discontinuous SiC/SiC CMCs. Advanced characterization techniquesScanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDX), Auger Electron Spectroscopy (AES), X‐ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM)—were used to analyze coated fibers. The findings reveal uniform, robust SiC coatings while preserving the BN layer. Notably, a stratified SiC structure, alternating between carbon‐rich and silicon‐rich zones, was observed. Auger spectroscopy and XPS provided insights into SiCx atomic composition and bonding environments. This research demonstrates TES's potential as an effective SiC precursor and advances understanding of FB‐CVD processes for short‐fiber coatings. The results pave the way for optimizing coating properties to enhance performance in SiC/SiC composites, opening new opportunities for further development.

Multiscale Modeling of Silicon Carbide Cladding for Nuclear Applications: Thermal Performance Modeling

The complex multiscale and anisotropic nature of silicon carbide (SiC) ceramic matrix composite (CMC) makes it difficult to accurately model its performance in nuclear applications. The existing models for nuclear grade composite SiC do not account for the microstructural features and how these features can affect the thermal and structural behavior of the cladding and its anisotropic properties. In addition to the microstructural features, the properties of individual constituents of the composites and fiber tow architecture determine the bulk properties. Models for determining the relationship between the individual constituents’ properties and the bulk properties of SiC composites for nuclear applications are absent, although empirical relationships exist in the literature. Here, a hierarchical multiscale modeling approach was presented to address this challenge. This modular approach addressed this difficulty by dividing the various aspects of the composite material into separate models at different length scales, with the evaluated property from the lower-length-scale model serving as an input to the higher-length-scale model. The multiscale model considered the properties of various individual constituents of the composite material (fiber, matrix, and interphase), the porosity in the matrix, the fiber volume fraction, the composite architecture, the tow thickness, etc. By considering inhomogeneous and anisotropic contributions intrinsically, our bottom-up multiscale modeling strategy is naturally physics-informed, bridging constitutive law from micromechanics to meso-mechanics and structural mechanics. The effects that these various physical attributes and thermo-physical properties have on the composite’s bulk thermal properties were easily evaluated and demonstrated through the various analyses presented herein. Since silicon carbide fiber-reinforced SiC CMCs are also promising thermal–structural materials with a broad range of high-end technology applications beyond nuclear applications, we envision that the multiscale modeling method we present here may prove helpful in future efforts to develop and construct reinforced CMCs and other advanced composite nuclear materials, such as MAX phase materials, that can service under harsh environments of ultrahigh temperatures, oxidation, corrosion, and/or irradiation.

A review on high-performance SiCf/SiC composites prepared by PIP process

Silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) are considered as a promising material for aero-engine hot-end structural components. The polymer infiltration and pyrolysis (PIP) process offers the benefits of high cost-effectiveness, adjustable preparation temperatures, and the ability to fabricate components with complex shapes. The manufacture of high-performance SiCf/SiC composites using the PIP process has become a research focus. This review briefly generalizes the synthesis methods of polycarbosilane and the specific process of polycarbosilane converting into SiC ceramics during pyrolysis. In addition, the physical and mechanical properties of SiCf/SiC composites prepared by the PIP process in recent years are discussed. Furthermore, this review summarizes some improvements to address the shortcomings of the PIP process, including adding fillers and combining other processes to assist the PIP process. At last, the future development trend of high-performance SiCf/SiC composites prepared by the PIP process is prospected.

High-entropy engineering improved the corrosion resistance of rare earth tantalates

High-entropy RETa3O9 ceramics have garnered significant interest in materials science due to their impressive high melting points and lower thermal conductivity. This study focuses on three types of these ceramics: (La0.2Ce0.2Nd0.2Sm0.2Dy0.2)Ta3O9, (La0.2Ce0.2Nd0.2Sm0.2Tm0.2)Ta3O9, and SmTa3O9.The results indicate that the coefficient of thermal expansion (TEC) for RETa3O9 ceramics remains in the range of approximately 5.94×10-6 K-1 to 6.05×10-6 K-1 when subjected to temperatures from room temperature up to 1400°C. This TEC is notably similar to that of silicon carbide ceramic matrix composites (SiC-CMC), which is essential for compatibility in applications where these materials are used together.Moreover, the study highlights an important finding: after 20 hours of exposure to a CMAS (calcium-magnesium-alumino-silicate) environment at 1300°C, the high-entropy tantalates exhibit significantly reduced susceptibility to corrosion compared to traditional single-component tantalate ceramics. While single-component materials, including SmTa3O9, showed greater degradation, the high-entropy RETa3O9 ceramics maintained their original morphology, free from porosity and cracking.This impressive resistance to CMAS corrosion indicates that the high-entropy design is beneficial in enhancing the durability of tantalates in extreme environments. Consequently, these findings suggest that high-entropy RETa3O9 ceramics hold promise for use as thermal/environmental barrier coating (T/EBC) materials in applications involving SiC-CMCs, potentially leading to improved performance and longevity in high-temperature applications.

Identification of component material in-situ properties of C/SiC composites based on self-consistent clustering analysis and Bayesian method

In the paper, a method for identifying the mechanical properties of the in-situ component materials in carbon fiber reinforced silicon carbide ceramic matrix composites based on the macro mechanical test data is proposed. Firstly, the computation efficiency of considering damage behavior in the meso-mechanial model is improved through the self-consistent clustering analysis. Subsequently, sensitivity analysis is introduced in the parameter identification based on the Bayesian network to reduce the number of parameters to be identified simultaneously, thereby alleviating the ill-posedness of the inverse problem. Numerical and experimental cases were conducted to validate the proposed method. The maximum error of parameter identification is 6.0 % and the prediction error for strength is only 1.7 % in the numerical case with 5 % Gaussian noise. In the experimental case, the stress–strain curve calculated using the identified results shows good agreement with the experimental data. The prediction error for strength is only 2.2 %, while the maximum deviation between the identified results and the reference value in the literature can be up to 50 %, indicating the importance of obtaining the properties of component materials in-situ.

Internal damage evolution of C/SiC composites in air at 1650 °C studied by in-situ synchrotron X-ray imaging

Carbon fibre reinforced silicon carbide (C/SiC) ceramic matrix composites have attracted considerable attention due to their exceptional properties and extensive potential applications as high-temperature structural materials. However, due to their complex structure and manufacturing defects, C/SiC composites exhibit intricate mechanical behaviour under thermal-mechanical-oxidative coupling environments. To date, systematic studies on the internal damage evolution and failure mechanisms of C/SiC composites under high-temperature oxidative environments are lacking. In this study, a combination of synchrotron X-ray micro-computed tomography (SR-μCT) and in-situ experiments under thermal-mechanical-oxidative coupling environments at room temperature and 1650 °C in air was used to characterize the internal microstructures and damage evolution processes of C/SiC composites at different loading levels. Additionally, the 3D strain fields during in-situ loading were quantitatively analysed using the Digital Volume Correlation (DVC) method. The findings underscore the substantial impact of oxidative damage on the mechanical response of C/SiC composites, particularly concerning tensile properties and fracture modes. At room temperature, severe delamination, fibre bundle pull-out and interfacial debonding occurred internally. Whereas, under high-temperature atmospheric conditions, severe fibre oxidation reactions occurred at the specimen edges, resulting in rapid porosity escalation. Crack initiation from surface defects followed by rapid inward propagation is observed. Moreover, while the strain distribution remains relatively uniform until fracture, a pronounced concentration of strain is evident near the fracture zones at room temperature, with an even greater concentration observed at 1650 °C. Notably, the region of concentrated strain within the 3D deformation field corresponds closely to the final fracture location, as revealed by quantitative DVC analysis.

Investigation of Titanium Nitride as an Effective Interphase for Carbon-Fiber-Reinforced Silicon Carbide Ceramic Matrix Composites.

Ceramic matrix composites (CMCs) have played a significant role in increasing the efficiency of gas turbine engines. CMCs combine the high temperature resistance of ceramics with the high mechanical strength of ceramic fibers into a single unit. Interphase layers are a crucial component in CMCs, as they prevent ceramic fibers from oxidation and introduce strengthening mechanisms into the composite. Hexagonal boron nitride and pyrolytic carbon are the most commonly used interphase layers in the aerospace industry. Other than that, very few materials have been evaluated as interphase layers. In this study, we explore the possibilities of using titanium nitride as an interphase layer in single-tow CMCs (mini composite) representative of a unidirectional composite at a smaller scale. T-300 carbon fibers were coated with TiN by atmospheric pressure chemical vapor infiltration using TiCl4, N2, and H2. The deposition temperature, precursor flow rate ratio, total precursor flow rate, and deposition time were optimized to obtain high-quality coatings. The best coating was produced at 800 °C, 4:1 H2 [TiCl4]/N2 ratio, 125 standard cubic centimeters per minute (N2 + H2 [TiCl4]) total flow precursor flow rate, and 2 h of deposition time. At these conditions, the coatings displayed good fiber coverage, good fiber adhesion, minimum fiber linkage, and minimum surface roughness. There was minimum fiber degradation after TiN coating, with a retention of 95% of the initial Young's modulus and 26% of the ultimate tensile strength of the carbon fiber. Adding the TiN interphase coating to the Cf/SiC CMC increased the ultimate tensile strength of the composite by 1122% and Young's modulus by 150%.

Recent progress on wet-oxygen corrosion resistance of SiCf/SiC composites

Being an aero-engine hot-end structural material, silicon carbide fiber (SiCf) reinforced silicon carbide (SiC) ceramic matrix composites (SiCf/SiC) display remarkable application potential. The wet-oxygen environment inside the aero-engine erodes the composites and leads to their performance degradation, which has become a key factor limiting the long-time service of SiCf/SiC. Finding an appropriate way to improve the wet-oxygen corrosion resistance of the composites is worthy of attention. This paper briefly analyzes the mechanisms of wet-oxygen corrosion and reviews the research progress in modified SiCf/SiC from three aspects: coatings, matrix, and interface. At last, the future development trend of the composites against the wet-oxygen environment is prospected.

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

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

Investigation on high-precision drilling of Cf/SiC composites with brazed diamond core-drill

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have promising applications as lightweight and hot end components due to their unique mechanical and high-temperature properties. However, high-precision drilling of Cf/SiC composites is still a difficult task, which is attributed to material's high hardness, anisotropy, and heterogeneity. In this work, a kind of core-drill with cemented carbide as shank and polycrystalline diamond (PCD) as grits, was prepared with vacuum brazing method. Experiments on drilling of 2D-Cf/SiC composite with the brazed core-drill were carried out. The effects of drilling parameters on the hole dimensional accuracy, surface roughness and defects were investigated. The results showed that with the increase of spindle speed and the decrease of feed rate, the dimensional accuracy was improved and surface roughness was reduced. Delamination, burr, and hole edge collapse were the main defects. The feed rate had a significant influence on the formation of defects. When the feed per revolution was equivalent to the diameter of a single carbon fiber, the defects were reduced effectively and the hole quality was improved substantially. In the investigated range of parameters, the optimal spindle speed and feed rate for high-precision drilling of Cf/SiC composites were 5000 r/min and 30 mm/min, respectively. Under this condition, the hole dimension accuracy was IT 10, and barely defects were observed on the machined surface. The surface roughness of hole sidewall reached a minimum value of 1.9 μm. This work provides a vital process for high-precision drilling on fiber reinforced ceramic matrix composites.

Nano-roughness effect on the interfacial thermal oxidation and surface catalytical recombination characteristics for silicon carbide based materials under non-equilibrium flow

With the rapid development of high-speed aircraft, the demanding for light, strong, reliable and high temperature resistive thermal protection material (TPM) is becoming urgent. High temperature material interface, such as silicon carbide (SiC) ceramic matrix composite, has received strong interest recently due to its high mechanical and thermochemical stability. For reactive interface development with nano-roughness under extremely hyperthermal non-equilibrium flow conditions for TPM applications, however, has not been reported yet. This work performs a systematic reactive molecular dynamics (RMD) study of the SiC surface morphology effect withstanding hyperthermal atomic oxygen (AO) impact via a gas–solid interface reaction model. The results show that a self-healing trend of the defect-rich silicon carbide surface with original nano-roughness is revealed towards a flatter interface accompanying with the oxidation process. The surface catalytic recombination coefficient is more sensitivity to the surface defects when wall temperature Tw > 500 K. Nano-roughness structure can also vary the main thermochemical reaction path at the thermochemical reactive interface: For the nano-groove surface model, the thermal oxidation reaction becomes dominant, while more pronounced surface catalytic recombination characteristics are revealed for the flat surface model. The mechanisms of roughness effect, surface temperature and gas impacting angle on the surface catalytic recombination, surface oxidation, and interface evolution are revealed, which advance our microscopic understanding of SiC interfacial performance with nano-roughness under non-equilibrium flow conditions.

Continuous Carbon Fiber Reinforced SiC Ceramic Matrix Composites by Vertical Fiber Laying Combined with Material Extrusion 3D Printing

3D printing is reported in the fabrication of continuous carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC CMCs), however, there are layer defects in the 3D printed materials, manifested as weak mechanical properties between layers. Therefore, it is essential and urgent to study how to improve the mechanical properties of 3D printed Cf/SiC CMCs at the layers. In this article, a novel processing technique which combined vertical fiber laying method with material extrusion (ME) 3D printing is proposed to manufacture Cf/SiC CMCs. A self‐developed 3D printing fixed‐axis rotating lifting synchronizer is adopted. The vertical fiber laying of continuous carbon fibers (Cf) in Z‐direction is introduced into the X−Y printing plane. Five cycles of precursor infiltration and pyrolysis (PIP) are performed to achieve the densification of Cf/SiC CMCs. The effects of Cf bundle numbers on the flexural strength and fracture work of Cf/SiC CMCs are studied. The best performing composite is Cf/SiC CMC with six bundles, and the maximum flexural strength and fracture work is 63.84 ± 6.62 MPa and 1291.99 ± 161.39 J m−3, respectively. Compared with pure SiC, the fracture work of Cf/SiC CMC with 6 bundles Cf is increased by 2.54 times.

Investigation of Yb2SiO5/BSAS/Si coating on Cf/SiC composites: processing and steam corrosion behavior

Environmental Barrier Coatings (EBCs) are used to protect silicon carbide-based composites in the high-temperature steam combustion environment of the latest generation of high-efficiency gas turbine aero-engines. The Yb2SiO5/BSAS/Si coatings with gradient coefficient of thermal expansion were prepared using atmospheric plasma spraying (APS) method on the carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC) composites surface. The coating preparation process parameters were optimized by evaluating the influence of spraying power on the bonding strength, deposition efficiency, and porosity. The corrosion behaviors and mechanism of the optimized Yb2SiO5/BSAS/Si coating was investigated at 1200 ℃ by thermal cycle test in steam conditions. The results indicated that the decomposition of Yb2SiO5 and the conversion of SiO2 to Si(OH)4 were the main corrosion reactions of Yb2SiO5 top coating. Noticeably, the SiO2 component acted as an obvious sign of the reaction front diffusing, forming the clear SiO2-gradient layers. The gradient Yb2SiO5/BSAS/Si coating remained intact after thermal cycles for 500 h at 1200 ℃ in steam conditions which effectively enhanced the resistance of Cf/SiC composites to high temperature steam corrosion.

Processing characteristics and ablation mechanism of CMC-SiCf/SiC by rotational thirteen-beam coupling nanosecond laser

Silicon carbide fiber reinforced silicon carbide ceramic matrix composite (CMC SiCf/SiC) has the advantages of high temperature resistance, corrosion resistance, high strength, low density, and oxidation resistance. It is a high-performance advanced material in aerospace, energy and other fields. However, due to its high hardness, brittleness and anisotropy of fiber structure, the research on application-oriented high-quality processing technology has become a hot issue. In this paper, a new process of rotational thirteen-beam coupling nanosecond laser processing of CMC-SiCf/SiC was studied. The rotational thirteen-beam coupling ablation experiments were carried out on CMC-SiCf/SiC workpiece. A laser beam is divided into thirteen beams and rotated around the beam center by using a beam splitter element. The morphology, structure and composition of ablation holes at different speeds were observed and analyzed by laser confocal microscope, scanning electron microscope, and X-ray energy dispersive spectrometer. It is found that the characteristics of rotational beam coupling have a significant effect on the laser ablation morphologies. The results show that the ablation region of CMC-SiCf/SiC is elliptical due to the fast heat transfer of fibers. The energy density distribution of the waist section of the Gaussian like beam after beam coupling is similar to the “W" shape, and the central energy is lower than the surrounding energy, and the ablation holes also show a similar “W" shape. With the increase of rotational speed, the hole depth first decreased and then increased, the hole diameter and roundness first increased and then decreased, and the hole section was “W" shaped. The ablation area can be divided into five parts: the white granular SiO2 solid coverage area, the recast layer, the lower recast layer, the molten layer, and the heat affected zone. The rotational characteristics will make the reaction intensity of the whole ablation area more uniform in the circumferential direction. The formation mechanism and element distribution of each part were explored. The research work in this paper will provide a new technical way for the high-performance application of CMC-SiCf/SiC.

Characterization, quantitative evaluation, and formation mechanism of surface damage in ultrasonic vibration assisted scratching of Cf/SiC composites

Carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC composites) have a wide range of applications in aerospace, nuclear energy, braking systems owing to its excellent mechanical performance. Nevertheless, the hardness, brittleness, heterogeneity, and anisotropy of Cf/SiC composites give rise to difficulties in machining them. In addition, the characterization and formation mechanism of surface damage in the grinding of Cf/SiC composites have not been fully elucidated. The purpose of this paper is to provide a characterization method for surface damage of Cf/SiC composites and an evaluation index for surface edge chipping damage (SECD) through conventional scratching (CS) / ultrasonic vibration assisted scratching (UVAS) tests with single abrasive. Towards revealing the surface damage behavior of Cf/SiC composites during scratching, as well as the impact of fiber orientation on surface damage. The findings indicate that main forms of surface damage of Cf/SiC composites in single abrasive scratching are fiber breakage, fiber fracture-shedding, fiber fracture, fiber-matrix interface debonding, interface fragmentation, matrix cracking, and matrix microcracks. Further, ultrasonic vibration could help to suppress the SECD, and the SECD factor was smallest when scratching along the perpendicular fiber. Furthermore, the fiber orientation can significantly affect the scratching force and cross-sectional area of scratches on Cf/SiC composites via single abrasive scratching. The tangential scratching force was usually smaller as compared to the normal scratching force, and the cross-sectional area of scratches in UVAS is smaller than that in CS. Based on the above findings, this study elucidates the formation and evolution of surface damage after scratching under different fiber orientations, filling the research gap in surface damage under ultrasonic assisted machining of Cf/SiC composites and providing technical guidance for the machining.

Multi-layered environmental barrier coatings designed on basis of YbTaO4-Ta2O5 composites for protecting SiCf/SiC composites

YbTaO4-Ta2O5 composites were designed and different multi-layered YbTaO4-Ta2O5/Yb2Si2O7/Si (YbT-T/YbDS/Si) as well as YbTaO4-Ta2O5/Si (YbT-T/Si) environmental barrier coatings (EBCs) were put forward to protect SiC fiber reinforced silicon carbide (SiCf/SiC) ceramic matrix composites (CMCs). The thermal cycling and the water-vapor/oxygen corrosion behavior of different multi-layered EBCs were compared. Results indicated that the thermal cycling lifetime of the bi-layered YbT-T/Si EBCs was similar with the tri-layered YbT-T/YbDS/Si ones. The ultimate failure of these two EBCs was induced by the cracking of the SiCf/SiC substrates as well as the vertical cracks associated with the thermal mismatch stress among different layers. However, the tri-layered EBCs exhibited greater resistance to water-vapor/oxygen corrosion than the bi-layered ones, primarily due to that the tri-layered YbT-T/YbDS/Si EBCs contained significantly less cracks than the bi-layered ones, limiting the transport of reactant (oxygen and/or water vapor) to reach Si bond coat.

Development Strategy of Continuous Silicon-Carbide-Fiber-Reinforced Silicon Carbide Ceramic Matrix Composites in the Field of Advanced Nuclear Energy

Development Strategy of Continuous Silicon-Carbide-Fiber-Reinforced Silicon Carbide Ceramic Matrix Composites in the Field of Advanced Nuclear Energy

Multi-Scale Characterization of Porosity and Cracks in Silicon Carbide Cladding after Transient Reactor Test Facility Irradiation

Silicon carbide (SiC) ceramic matrix composite (CMC) cladding is currently being pursued as one of the leading candidates for accident-tolerant fuel (ATF) cladding for light water reactor applications. The morphology of fabrication defects, including the size and shape of voids, is one of the key challenges that impacts cladding performance and guarantees reactor safety. Therefore, quantification of defects’ size, location, distribution, and leak paths is critical to determining SiC CMC in-core performance. This research aims to provide quantitative insight into the defect’s distribution under multi-scale characterization at different length scales before and after different Transient Reactor Test Facility (TREAT) irradiation tests. A non-destructive multi-scale evaluation of irradiated SiC will help to assess critical microstructural defects from production and/or experimental testing to better understand and predict overall cladding performance. X-ray computed tomography (XCT), a non-destructive, data-rich characterization technique, is combined with lower length scale electronic microscopic characterization, which provides microscale morphology and structural characterization. This paper discusses a fully automatic workflow to detect and analyze SiC-SiC defects using image processing techniques on 3D X-ray images. Following the XCT data analysis, advanced characterizations from focused ion beam (FIB) and transmission electron microscopy (TEM) were conducted to verify the findings from the XCT data, especially quantitative results from local nano-scale TEM 3D tomography data, which were utilized to complement the 3D XCT results. In this work, three SiC samples (two irradiated and one unirradiated) provided by General Atomics are investigated. The irradiated samples were irradiated in a way that was expected to induce cracking, and indeed, the automated workflow developed in this work was able to successfully identify and characterize the defects formation in the irradiated samples while detecting no observed cracking in the unirradiated sample. These results demonstrate the value of automated XCT tools to better understand the damage and damage propagation in SiC-SiC structures for nuclear applications.

Cf/SiC Ceramic Matrix Composites with Extraordinary Thermomechanical Properties up to 2000 °C.

The thermomechanical properties of carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC CMCs) were studied up to 2000 °C using high-temperature in situ flexural testing in argon. The CMC specimens were fabricated using an ultrahigh concentration (66 vol%) aqueous slurry containing nano-sized silicon carbide powder. The SiC powder compacts were obtained by drying the slurry and were densified using the precursor impregnation and pyrolysis (PIP) method with field assisted sintering technology/spark plasma sintering (FAST/SPS). The high relative density of the SiC green body (77.6%) enabled densification within 2.5 days using four PIP cycles. In contrast, conventional PIP processes take over 7 days. The in situ flexural strength of the Cf/SiC CMC was 434 MPa at 1750 °C, which was 84% higher than the room temperature value. The value further increased to 542 MPa at 2000 °C. Possible mechanisms to explain the excellent strength of the CMC at elevated temperatures are discussed.

Effect of tool wear on machining quality in milling Cf/SiC composites with PCD tool

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have great application potential in aerospace. But their high hardness and anisotropy cause rapid tool wear during machining, which affects machining quality and efficiency. However, tool wear mechanisms in milling Cf/SiC composites are still unclear. There is a lack of research on the relationship between tool wear and cutting performance. In this paper, milling experiments on 2.5D Cf/SiC composites were conducted using polycrystalline diamond (PCD) cutters. The tool wear mechanisms and effect of tool wear on surface roughness, milling force, burr damage, surface microstructure and chips were explored. The results show that abrasive wear caused by chips continuously scraping tool material and diamond particle fragmentation and falling off caused by sprouting and expansion of cracks inside grain were primary causes of tool failure. The formation mechanism of burr damage was analyzed. It was proved that the peak radius of cutting edge Rpeak and flank wear VB could reflect cutting capabilities. It was found that increasing flank wear had regrinding effects on the cutting edge, which affects the peak radius. The degree of burr damage was related to these two parameters. Tool wear changed the surface formation mechanism. Before tool wear, carbon fibers were primarily removed through the micro-brittle fracture, with low surface roughness. The flank face and chips scratched the workpiece like abrasive grains after tool wear, leaving scratches on the surface and increasing surface roughness from 1.27 μm to 2.25 μm.