Reinforced Silicon Carbide Ceramic Matrix Research Articles

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.

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.

On understanding the mechanical properties and damage behavior of Cf/SiC composites by indentation method

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have the advantages of high temperature resistance, wear resistance, low density, high hardness as well as specific strength. They have been applied extensively in hot-end components of aerospace and braking systems of trains. Nevertheless, grappling with the anisotropy, non-homogeneity, and weak interlayer bonding of Cf/SiC composites presents a major challenge for achieving efficient and low-damage processing. This paper is primarily intended to investigate comprehensively the mechanical properties and damage behavior of Cf/SiC composites by nanoindentation and Vickers indentation tests. The behaviors of indentation damage on the longitudinal section of fiber (LSF), the cross-section of fiber (CSF) and matrix under different loads and the deflection mechanism of matrix crack were analyzed. The findings reveal a pronounced anisotropy between the radial and axial orientations of the fiber, and plastic deformation exists in the matrix. Furthermore, the matrix has the largest hardness and elastic modulus, while the LSF displays the lowest values among the composites. The main forms of indentation damage on the LSF are fiber crack, fiber peel off, fiber cocked up and squamous crack. The main manifestations of indentation damage on CSF are fiber crushing and fiber debonding, with the total surface damage area being comparatively limited. The fiber orientation and interface are influential factors in the crack propagation path of matrix. Notably, the fibers effectively inhibit the crack propagation of the matrix. This investigation provides valuable theoretical guidance for the formation mechanism and suppression strategy of machining damage in Cf/SiC composites.

Investigations on the effect of ultrasonic vibration on fibre fracture and removal mechanism in cutting of fibre reinforced silicon carbide ceramic matrix composites

To clarify the effectiveness of ultrasonic vibration-assisted cutting (UVAC) technology for improving the surface quality of FRCMCs-SiC, it is necessary to have a deep understanding of fibre fracture and removal mechanism of UVAC. The paper focuses on the feasibility and effect of UVAC technology on improving the machined surface quality of FRCMCs-SiC combining finite element model (FEM). The results show that applying ultrasonic vibration (UV) along the cutting direction, whether in the micro brittle fracture regime or the macro brittle fracture regime, is beneficial to reduce the cutting force, the machined surface roughness and the depth of the subsurface damage. When UV is applied perpendicular to the cutting direction, it can promote fibre fracture in the macro brittle fracture regime and reduce the depth of the subsurface damage, but deteriorate the machined surface quality in the micro brittle fracture regime.

Material Removal Behavior of Ultrasonic Vibration Helical Grinding of SiCf/SiC Composites

Abstract To reveal the material removal mechanism of silicon carbide fiber reinforced silicon carbide ceramic matrix (SiCf/SiC) composites during the ultrasonic vibration helical grinding (UVHG) of hole-making process, a hole-making experiment of UVHG was conducted, and the contact behavior between a grain and different components in the SiCf/SiC was analyzed. The evaluation index of the hole wall quality Cw which comprehensively considers the overall level and local defects of surface quality was proposed, while the evaluation index of the hole exit quality Ce which comprehensively considers the area and depth of edge chipping was proposed too. The results show that the periodic changes of the fiber cutting angle θ will lead to different fracture mechanisms of the fibers and the interfaces, so the surface topography will change regularly. The brittle fracture of the matrixes under different process parameters is different, so the surface topography is different. The quality evaluation indexes Cw and Ce are highly reliable. Within the experimental parameters, selecting a smaller pitch, a smaller helical feed rate, and an appropriate ultrasonic amplitude can obtain better hole-making quality.

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.

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.

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.

Effect of ceramic surface texture on the tribological property of ceramics and carbon fiber reinforced silicon carbide ceramic matrix composite (C/SiC)

Three processing methods including grinding, polishing, laser engraving were used on ZrO2 and Si3N4 surfaces. Two types of surface textures were obtained including micro dimples and micro grooves through the laser engraving. Therefore, the friction experiments of the eight surfaces mated with C/SiC were conducted under a dry condition at ambient temperature. The results indicated that surface texture does not necessarily have a positive effect on the tribological properties which are largely influenced by the countrpart materials and the texture type. Ground ZrO2-C/SiC and Si3N4 with micro dimples-C/SiC have a better tribological property, and the former shows the best performance during the tests. The formation and the falling off of wear debris are accompanied with the whole friction process while C/SiC rubbing against Si3N4 disc with micro dimples thus resulting in a worse result.

Heat Insulation Performance of Lattice Thermal Protection Structure with Reinforced Plate

A lightweight lattice structure is proposed, which can be applied to the thermal protection system of high speed aircraft. The structure uses carbon fiber reinforced silicon carbide ceramic matrix composite as the framework, and the inner cavity can be filled with heat insulation materials with small thermal conductivity. In order to study the heat insulation performance of the structure, the three-dimensional finite element heat transfer model of the lattice structure with and without heat insulation material was established. Abaqus software was used to calculate the temperature distribution and change of the lattice structure under different temperature boundary conditions. The equivalent thermal conductivity of the lattice structures under different temperature boundary conditions is defined and calculated. The results show that the heat insulation effect of the lattice structure is improved obviously with the addition of heat insulation materials, but the time required to reach the stable state is increased. Without heat insulation materials, the strength of cavity radiation is greatly affected by the temperature boundary conditions on the top surface and positively correlated. Increasing heat insulation materials can effectively block the generation of cavity radiation, thus enhancing the heat insulation effect. The conclusion provides a foundation for further application of the lattice structure in thermal protection system of high speed aircraft.

Experimental Study on High-Speed Milling of SiCf/SiC Composites with PCD and CVD Diamond Tools.

Silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiCf/SiC composite) is characterized by a high strength-to-density ratio, high hardness, and high temperature resistance. However, due to the brittleness of the matrix material and the anisotropy of the reinforcing phase, it is a huge challenge for machining of the material. The milling method has advantages of a high material removal rate and applicability to complex surface geometry. However, no published literature on milling of SiCf/SiC composite has been found up to now. In this paper, high-speed milling of SiCf/SiC composites was carried out under dry conditions and cryogenic cooling using liquid nitrogen, respectively. Polycrystalline diamond (PCD) and chemical vapor deposition (CVD) diamond cutting tools were used for the milling work. The cutting performance of the two kinds of tools in high-speed milling of SiCf/SiC composites was studied. Tool failure modes and mechanisms were analyzed. The effects of the cooling approach on tool wear and machined surface quality were also investigated. The experimental results showed that under identical cutting parameters and cooling approaches, the PCD tool yielded better cutting performance in terms of a longer tool life and better surface quality than that of the CVD diamond tool. In dry machining, the failure modes of the CVD diamond tool were a large area of spalling on the rake face, edge chipping and severe tool nose fracture, whereas for the PCD tool, only a small area of spalling around the tool nose took place. Compared to the dry machining, the wear magnitudes of both PCD and CVD diamond tools were decreased in cryogenic machining. Additionally, the surface quality also showed significant improvements. This study indicates that the PCD tool is highly suitable for machining of SiCf/SiC composite, and that the cryogenic method can improve machining efficiency and surface quality.

Effects of grinding speed on the material removal mechanism in single grain grinding of SiCf/SiC ceramic matrix composite

Silicon carbide (SiC) fibers reinforced SiC ceramic matrix composite (SiCf/SiC) is an advanced material for aeroengines because of its high-temperature resistance and high specific strength. However, it is rather difficult to machine. Though there have been many methods available for machining SiCf/SiC, the material removal mechanism is not fully understood and the machining efficiency is still low. This paper studies the effects of grinding speed on the material removal mechanism of SiCf/SiC by single grain grinding. Results indicate that increasing speed grinding could embrittle the material and enhance the breakage of fibers. When grinding along the fiber longitude direction, fibers present brittle fracture and matrix is torn off in high speed grinding rather than the ploughing in fibers or the smearing in matrix in low speed grinding. When grinding transverse to the fiber longitude direction, fibers are removed completely without any residual cut-off fiber end which is common in low speed grinding. Both the groove surface quality and machining efficiency are improved by increasing speed grinding.

Influences of clearance angle and point angle on drilling performance of 2D Cf/SiC composites using polycrystalline diamond tools

Cf/SiC composite (carbon fiber reinforced silicon carbide ceramic matrix composites) is a kind of advanced composite material constituted by SiC as matrix and carbon fiber as reinforcing phase. Cf/SiC composites are being extensively used in the modern aerospace industry owing to their excellent physical and mechanical properties. The current work aims to investigate influences of clearance angle and point angle on drilling performance of 2D Cf/SiC composites using PCD (polycrystalline diamond) tools in terms of thrust force, drilling torque, hole surface quality, and material removal mechanism. PCD drill bits with different point angles and clearance angles were used in the experiment. The obtained results indicate that the 150° point angle is beneficial to improve the hole surface quality, and larger clearance angle is helpful to reduce the damage of exits. Additionally, the variation of clearance angle has little effect on the roughness of the machined surface. During the drilling process, the dominated material removal mechanisms are matrix removal, fiber breakage, and matrix-fiber debonding. The brittle fracture mode of carbon fibers, which directly affects surface roughness, can be divided into micro-brittle fractures in carbon fiber and macro-brittle fractures. Besides, the damage identification method of hole entrance and exit based on image processing technology is helping to improve the efficiency of machining quality evaluation.

Measurement and evaluation of fiber bundle surface of long fiber reinforced woven composites

Long fiber reinforced woven composites (LFRWCs) are being applied to many growing fields because of their excellent properties; however, owing to their anisotropy and inhomogeneity, traditional surface measurements and evaluation methods appropriate for isotropic materials are no longer suitable to LFRWC, thus causing many difficulties in terms of their wide industrial applications. Based on this fact, a multi-scale surface evaluation system is proposed according to the LFRWC structure. This paper is mainly focused on the first scale evaluation-fiber bundle scale. First, the reasons why 2D rather than 3D measurements and evaluations should be adopted at this scale are described, and four indexes, namely, Raave, Rqave, Rskave and Rkuave are proposed to evaluate the surface roughness, damage type, and degree of damage. A method is proposed to determine the maximum sampling step (MaxSS) to ensure that the measurement data are undistorted. As a demonstration, the validity of the method is checked through the testing of a carbon fiber reinforced silicon carbide ceramic matrix composite (Cf/SiC).