Silicon Carbide Ceramic Matrix Composites 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.

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.

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.

Interactions of Na2SO4 and yttrium‐silicate environmental barrier coatings at 825°C

AbstractYttrium‐silicates (Y2Si2O7 and Y2SiO5) are candidate environmental barrier coating (EBC) materials for silicon carbide ceramic matrix composites (SiC‐CMCs). These materials’ high‐temperature, high‐velocity steam, and siliceous debris resistance are well studied. However, Na2SO4‐induced hot corrosion mechanisms are less understood. Free‐standing atmospheric plasma sprayed Y2Si2O7 and Y2SiO5 coupons were exposed to 2.5 mg/cm2 of Na2SO4 at 825°C in 0.1% SO2‐O2 (g). Scanning electron microscopy, X‐ray diffraction, transmission electron microscopy, and inductively coupled plasma‐optical emission spectrometry were used to identify a previously unknown damage mechanism. Water‐soluble Y and Na‐Y sulfates and oxysulfates formed in reaction with Na2SO4, causing significant damage to the yttrium‐silicate EBCs materials.

Fine study of hierarchical interphase constructed by Ti3SiC2 and carbon nanotubes in SiCf/SiC composites

The interphase in silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) assumes a significant role in the mechanical properties exhibited at elevated temperatures. The strength, toughness, and chemical stability of a composite is frequently influenced by the optimization of its interphase. In this work, the MAX phase (Ti3SiC2) and carbon nanotubes (CNTs) were successively deposited on the SiCf using the molten salt method and chemical vapor deposition technique, respectively, to create a hierarchical structure. Transmission electron microscopy was employed to undertake a comprehensive investigation of the interfacial component in SiCf/SiC composites. The detailed study of interphases in SiCf/SiC composites has been conducted through the analysis of crystallization, the bonding natures, and the micromorphology, encompassing geometry and constituent characteristics. A bilayer consisting of TiC–Ti3SiC2/Ti5Si3 and a vertical array of carbon nanotubes (CNTs) with a length of 7 μm is fabricated on the surface of SiCf/Ti3SiC2-CNTs. The SiCf/Ti3SiC2/SiC and SiCf/Ti3SiC2-CNTs/SiC composites exhibit lamellar structures of Ti3SiC2, which indicates a further crystallization of Ti3SiC2 resulting from the formation of SiC matrix by PIP procedure. The interphase of SiCf/Ti3SiC2-CNTs/SiC composite may be categorized into four distinct layers: a TiC phase, a TiSi2 phase, a transition phase of TiSi2/TiC, and a Ti3SiC2 phase. This interphase structure is more intricate compared to the interphase structure observed in the SiCf/Ti3SiC2/SiC composite. This research indicates significant value for the future design and optimization of interfaces.

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.

Large-scale material extrusion-based additive manufacturing of short carbon fibre-reinforced silicon carbide ceramic matrix composite preforms

ABSTRACT Large-scale short carbon fibre-reinforced silicon carbide (Csf/SiC) ceramic matrix composites (CMCs) have important applications in the field of aerospace engineering. This study proposed the use of material extrusion based additive manufacturing to fabricate large-scale C sf/SiC CMC preforms. In this paper, we determined how the key material extrusion parameters, including solid loading, nozzle diameter and layer height impact the stability of the additively manufactured C sf/SiC CMCs. The solid loading significantly influenced the stability of the C sf/SiC CMCs, and the slurry with 50 vol.% solid loading was better for additive manufacturing. The layer height played a significant role in the void formation in CMCs. It was appropriate for structure retention to set the layer height as 60–75% of the nozzle diameter. The effect of angle from vertical on the stability of out-of-plane structure was also investigated. When the angle was over 40o, the out-of-plane structure additively manufactured without supports tended to collapse. Large-scale C sf/SiC CMC preforms with out-of-plane structures were finally successfully fabricated. This study is believed to provide some fundamental understanding for the fabrication of large-scale fibre-reinforced ceramic matrix composites.

Temperature Resistance Properties of Unidirectional Laminated Cf/SiC-Al Prepared by PIP and Vacuum Pressure Infiltration.

Material used for aero-engine fan blade requires excellent mechanical properties at high temperature (300 °C). Continuous carbon-fiber-reinforced silicon carbide ceramic matrix composites (Cf/SiC) are necessary candidates in this field, possessing low density, high strength, high modulus, and excellent high-temperature resistance. However, during the preparation process of Cf/SiC, there were inevitably residual pores and defects inside, resulting in insufficient compressive strength and reliability. The vacuum pressure melting infiltration process was used to infiltrate low melting point and high wettability aluminum alloys into the porous Cf/SiC composite material prepared by the precursor impregnation cracking process, repairing the residual pore defects inside the body. The porosity of porous Cf/SiC decreased from 49.65% to 5.1% after aluminum alloy repair and strengthening. The mechanical properties of Cf/SiC-Al composite materials strengthened by aluminum alloy repair after heat treatment were studied. The tensile strength of the as-prepared Cf/SiC-Al was 166 ± 10 MPa, which were degraded by 13~22% after heat treatment. The nonlinear sections of stress-displacement curve of as-treated samples were shorter than that of as-prepared sample. The hardness of aluminum alloy matrix after 300 °C 1 h heat treatment was 58 Hv, which was not obviously reduced compared with the sample without heat treatment. The vacuum infiltration of aluminum alloy is expected to have guiding significance for repairing and strengthening internal defects in ceramic matrix composites.

Experimental investigation and prediction of ECDM parameters on fiber reinforced SiC composite using hybrid ERNN-based Sparrow Search Optimization

The Silicon Carbide (SiC) fiber-reinforced SiC ceramic matrix composites have proved their outstanding performance on high thermal applications such as gas turbine engine parts, turbo-pumps, nozzles, and various other aerospace/aero-propulsion system parts. Regardless of their enhanced strength properties, the SiC fiber-reinforced SiC ceramic composite materials are difficult to process using conventional machining methods. Also, SiC fiber-reinforced SiC ceramic promotes a higher tool wear rate while doing conventional drilling operations. Therefore, this study investigates the Electrochemical Discharge Machining (ECDM) parameters on such SiC fiber-reinforced SiC ceramic composite. Besides, the levels of most influencing ECDM input parameters Voltage, Electrolytic Concentration and Duty Cycle are optimized using a novel hybrid machine learning optimizer called Elman Recurrent Neural Network-based Sparrow Search Optimization (ERNN-SSO). The experiment is planned using Response Surface Methodology based on Box Behnken Design (RSM-BBD) and verified using ANOVA. The Material Removal Rate (MRR), Tool Wear Rate (TWR) and Overcut (OC) are considered output performances during this study. The proposed ERNN-SSO has optimized ECDM input parameters at a maximum of 0.03 root mean square error (RMSE), approximately 33 % and 95 % lower than the conventional ERNN and RSM optimization techniques. This study’s suggested ECDM input parameters for drilling SiC fiber-reinforced SiC ceramic composite are 95 V voltage supply, 10 %Wt. of electrolytic concentration, and 50 % duty cycle. Because, such optimum ECDM parameters produced a maximum MRR of 370 μg/min with minimum TWR and OC of 283 μg/min and 161 µm during this study.

Preparation and properties of highly thermal conductive C/C-SiC

A kind of highly thermal conductive silicon carbide matrix composites (c-1000/C-SiC, c-600/C-SiC) reinforced with chopped mesophase pitch-based carbon fibers (c-MPCF) including 1000 W/(m·K) and 600 W/(m·K) were successfully prepared by the phenolic resin precursor impregnation pyrolysis and liquid silicon infiltration (LSI) method. Quasi-isotropic c-MPCF/C-SiC composites demonstrate excellent thermophysical properties, including average flexure strength of 111.5 MPa of c-1000/C-SiC and 123.0 MPa of c-600/C-SiC, average high thermal conductivity of 101.33 W/(m·K) and 93.94 W/(m·K) at room temperature, low coefficient of thermal expansions of 2.942 ppm/K and 3.147 ppm/K at room temperature, which provides a new strategy for preparing isotropic silicon carbide ceramic matrix composites with comprehensive properties and dimensional stability.

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.

Identification of microstructures and damages in silicon carbide ceramic matrix composites by deep learning

Identification of microstructures and damages in silicon carbide ceramic matrix composites by deep learning

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.

Combination of direct ink writing and reaction bonded for rapid fabrication of SiCw/SiC composites

Silicon carbide ceramic matrix composites are widely used in aerospace field due to their advantages of high temperature resistance, high strength and corrosion resistance. However, its application is greatly limited because of the difficulty in preparing complex shape structures by traditional machining methods. Here, a new strategy for preparing SiC w /SiC complex structure by combining direct ink writing with reaction bonding is proposed. A water-based slurry consisting of silicon carbide, carbon powder and silicon carbide whisker was developed. The influence laws of C content and SiC w content in slurry on sintering properties of direct-written samples were studied. The reaction bonding mechanism and whisker reinforcing and toughening mechanism were analyzed by means of microstructure and phase composition. The results show that the slurry exhibits shear thinning behavior with stress yield point, and its flow behavior and plasticity meet the requirements of direct writing. When the carbon content is 6.4 wt%, the maximum flexural strength is 239.3 MPa. When 15 wt% SiC w was added, the flexural strength of the composite reached 301.6 MPa, and when 20 wt% SiC w was added, the fracture toughness of the composite reached 4.02 MPa m 1/2 , which was increased by 26% and 18% compared with single-phase SiC, respectively. The reinforcing and toughening mechanisms of the whiskers mainly include whisker pullout, crack deflection and whisker bridging. After direct ink writing and reaction bonded, the whole process shows good near net forming ability. 3D printed SiC w /SiC composites have great application prospects in aerospace field.

Modeling the two-way coupling of stress, diffusion, and oxidation in heterogeneous CMC microstructures

A multiphysics methodology and a corresponding numerical scheme are proposed for modeling the complex interactions between oxygen diffusion, matrix cracking, oxidation, and the state of stress in carbon silicon carbide (C/SiC) ceramic matrix composites (CMCs) at the microstructural scale. The model is derived from the governing equations for force equilibrium and conservation of mass for oxygen and carbon, which are coupled through reaction terms, oxygen diffusivities and solubilities, and damage in the matrix. The Galerkin method of weighted residuals is used to derive the finite element method (FEM) equations, and the model is demonstrated on a representative stochastic heterogeneous microstructure to investigate the creep-like strain acceleration of stressed oxidation experiments and analyze the fundamental differences between the reaction-limited and diffusion-limited temperature regimes.

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.