Ceramic Matrix Composites Research Articles

Regulating synergistic micro-nano pore structure of CNT sponge to control EMI shielding performance

The aggregation in high-content carbon nanotube reinforced silica carbide composites (CNT/SiC) imposed constraints for further large-scale industrial applications. This study established a synergistic micro-nano pore structure by assembling CNT bundles to fabricate the CNT sponge preform, and then the SiC matrix was in-situ deposited by chemical vapor infiltration method, which facilitates composites with high density and exceptional properties. The pore size distribution and pore area can be regulated by simply adjusting the compression ratios (CRs) of the as-assembled CNT sponge. Samples with CR of 50 % exhibited noteworthy densification, significantly reduced porosity, and a remarkable 163.54 % extra increase in compression strength compared to uncompressed ones. Additionally, the CNT/SiC composites displayed excellent oxidation resistance and demonstrated improved electromagnetic interference (EMI) shielding performance, which exhibited a substantial increase with higher CRs. These findings underscore the significance of employing appropriate multi-level porosity in CNT preforms to fabricate advanced ceramic matrix composites with superior EMI shielding capabilities.

Influence of spraying power on microstructure, phase composition and nanomechanical properties of plasma-sprayed nanostructured Yb-silicate environmental barrier coatings

Currently, achieving high stability for environmental barrier coatings (EBCs) in service at higher operational temperatures (>1400 °C) remains a challenging issue. In our previous work, a nanostructured Yb-silicate coating was successfully fabricated, which could be a promising EBC candidate for CMC (Ceramics Matrix Composites) components protection at higher temperatures. However, there have been limited reports on the relationship between mechanical properties and spraying power for producing a nanostructured Yb-silicate coating. Therefore, this study delves into the microstructure, phase composition, and nanomechanical properties of nanostructured Yb-silicate coatings before and after heat treatment at different spraying powers. The results indicate that, due to the intricate interplay of microstructural and phase composition evolution, noticeable disparities in nanomechanical properties were observed in nanostructured Yb-silicate coatings before and after heat treatment. It is noted that the as-sprayed coating at 36 kW exhibits comparable nanomechanical properties to 45.5 kW, whereas the heat-treated coating demonstrates higher nanohardness and elastic modulus at 36 kW but greater damage tolerance at 45.5 kW. These findings offer a preliminary guidance for optimizing process parameters in nanostructured Yb-silicate coating's preparation, and laying the foundation for further researches.

Virtual development of competitive products made of customized ceramic composites

Ceramic matrix composites (CMCs) are commonly employed in situations where conventional materials face limitations or when they could provide substantial performance enhancements. However, when the latter condition is met, the increased performance must offset the higher costs associated with development and manufacturing. In this study, a methodological approach is introduced to concurrently reduce costs and optimize performance via virtual product development and tailored material customization. The effectiveness of this approach is demonstrated using an antenna strut in the context of space applications as an illustrative example.Moreover, strategies are proposed for the integration of pre-existing simulation models. Relevant diagrams are provided for CMC customization, alongside the introduction of a cost model based on the cost-performance ratio in contrast to a reference product. As a result, the study significantly enhances the competitiveness of CMC components compared to conventional materials, ultimately expanding their market potential.

Line-of-sight gas radiation effects on near-infrared two-color ratio pyrometry measurements during plasma wind tunnel experiments

Two-color ratio pyrometry is commonly used to measure the surface temperature of aerospace materials during plasma wind tunnel experiments. However, the effect of the plasma radiation on the measurement accuracy is often neglected. In this paper, we formulate a model of the instrument response to analyze the systematic error induced by the gas radiation along the optical path. CFD simulations of the plasma flow field, together with a radiation code, allow to compute the gas spectral radiance within the instrument wavelength range. The measurement error is numerically assessed as a function of the true object temperature and emissivity value. Our simulations explain the typical behavior observed in experiments, showing that a significant bias can affect the measured temperature during the material heating phase. For an actual experiment on a ceramic-matrix composite, a correction to the measured data is proposed, while comparative measurements with a spectrometer corroborate the results.

Material design using calculation phase diagram for refractory high‐entropy ceramic matrix composites

AbstractTo achieve Si‐free refractory ceramic matrix composites exposed to an oxidizing atmosphere at approximately 2000°C, a Ti–Zr–Mo ternary alloy melt‐infiltration (MI) method was developed for the production of carbon fiber‐reinforced refractory high‐entropy ceramic matrix composites (C/RHECs), with high‐entropy carbides serving as the matrix. This approach was designed using calculation phase diagrams (CALPHADs) and the calculation of thermodynamic parameters. The combination of CALPHAD and the calculation of alloy and carbon reactivity enabled the prediction of reaction and infiltration behavior into a preform comprising carbon fiber, carbon black, and transition metal carbide powders. Furthermore, C/RHECs featuring a (Ti, Zr, Hf, Nb, Ta, Nb, Mo)C matrix were experimentally fabricated through the Ti–Zr–Mo alloy MI method in accordance with the design. The arc‐wind tunnel tests on the C/RHECs conducted at approximately 2000°C revealed surfaces covered with complex oxides. The apparent oxidation rate of the C/RHECs was similar to that of Si‐containing ceramics and composites. These results indicate that complex oxides act as a barrier to oxygen diffusion toward unoxidized regions, making Si no longer essential for protecting materials from oxidation above 2000°C.

Effect of BN interfacial layer on the mechanical behavior of SiC fiber reinforced SiC ceramic matrix composites

AbstractBoron nitride (BN) interfacial layer with controlled thickness and structure was prepared on the surface of near stoichiometric ratio SiC fiber preforms by a chemical vapor deposition process, and the SiC/SiC composites were obtained by polymer precursor infiltration and pyrolysis process. The microstructure of the BN interfacial layer and SiC/SiC composites was tested by scanning electron microscopy, and the mechanical behavior of SiC/SiC composites was characterized by a mechanical properties test. Results showed that BN interfacial layer was evenly distributed in the fiber preforms with excellent thickness consistency. As the thickness of the BN interfacial layer increased, the deflection path of the crack increased gradually, resulting in the flexural strength first increasing and then decreasing. The mechanical behavior mentioned above was mainly attributed to the dual effects of load transfer and crack propagation of the BN interfacial layer; that was, the crack propagation of ceramic matrix under external load lengthened the path of load transfer and formed a large number of fibers bridging and pulling out successively, which contributed to the energy dissipation mechanism.

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.

Study on grinding removal mechanism and subsurface damage of bionic layered graphene ceramic matrix composites

Study on grinding removal mechanism and subsurface damage of bionic layered graphene ceramic matrix composites

Thermo-Mechanical Stress Distributions in a Ceramic Matrix Composites Turbine Vane Coated with Environmental Barrier Coatings

It is of great significance to obtain an accurate stress assessment when replacing traditional metal components with ceramic matrix composites (CMCs) in turbine engines. The current study aims to investigate the stress characteristics of CMCs turbine vanes with multilayer-structured environmental barrier coatings (EBCs) using numerical simulation techniques. A three-dimensional finite element model of CMCs turbine vanes coated with EBCs was formulated. The distribution of thermal residual stresses generated during the manufacturing process of EBCs and the distribution of stresses under different loading conditions were calculated and compared. The results show that the hoop stress (σ11) and spanwise stress (σ22) in the turbine vanes are significantly higher than the through-thickness stress (σ33) under coupled loads. The maximum hoop stress (σ11) is approximately 346 MPa. The thermal residual stress induced during the EBCs manufacturing process reaches a maximum of approximately 360 MPa. The loading conditions significantly influence the stress distribution of EBCs, and the stress distribution of EBCs exhibits certain regularities at different heights under varying loading conditions. These results enable us to gain a deeper understanding of the failure mechanism of CMCs/EBCs turbine vanes and can improve the optimization capabilities for these components.

Review on Abrasive Machining Technology of SiC Ceramic Composites.

Ceramic matrix composites have the advantages of low density, high specific strength, high specific die, high-temperature resistance, wear resistance, chemical corrosion resistance, etc., which are widely used in aerospace, energy, transportation, and other fields. CMCs have become an important choice for engine components and other high-temperature component manufacturing. However, ceramic matrix composite is a kind of multi-phase structure, anisotropy, high hardness material, due to the brittleness of the ceramic matrix, the weak bonding force between fiber and matrix, and the anisotropy of composite material. Burr, delamination, tearing, chips, and other surface damage tend to generate in the machining, resulting in surface quality and strength decline. This paper reviewed the latest abrasive machining technology for SiC ceramic composites. The characteristics and research directions of the main abrasive machining technology, including grinding, laser-assisted grinding, ultrasonic-assisted grinding, and abrasive waterjet machining, are introduced first. Then, the commonly used numerical simulation research for modeling and simulating the machining of ceramic matrix composites is briefly summarized. Finally, the processing difficulties and research hotspots of ceramic matrix composites are summarized.

Design aspects of a CMC coating-like system for hot surfaces of aero engine components

Ceramic Matrix Composite (CMC) is an emerging material system that can be a game changer in the aerospace industry, both civil and military. CMCs components are, in fact, lighter and less prone to fatigue failure in a high temperature environment. However, at high temperatures, the diffusion of oxygen and water vapour inside the CMC can have detrimental effects. Therefore, the presence of protective coating is necessary to extend the life of CMC components. In the present work, a three-layers coating, consisting of a silicon bond (BND), adhesively bonded to the CMC, an Environment Barrier Coating (EBC) and a softer layer 3 (LAY3), is investigated for a CMC component. An aero-engine high pressure turbine seal segment was considered. Two design aspects are covered: (i) creep law is determined and calibrated in environment Abaqus from the experimental data of each coating layer available in the open literature, to provide a suitable instrument for the creep relaxation analyses of hot components; (ii) thickness sensitivity study of each layer of the coating is conducted to minimise the interface stresses of coating with substrate in order to mitigate cracking and removal/spalling phenomena when exposed to temperature gradients and to increase their service life. These two different aspects are combined together to predict the coating stress field as a function of service time.

Theoretical Prediction of Thermal Expansion Anisotropy for Y2Si2O7 Environmental Barrier Coatings Using a Deep Neural Network Potential and Comparison to Experiment.

Environmental barrier coatings (EBCs) are an enabling technology for silicon carbide (SiC)-based ceramic matrix composites (CMCs) in extreme environments such as gas turbine engines. However, the development of new coating systems is hindered by the large design space and difficulty in predicting the properties for these materials. Density Functional Theory (DFT) has successfully been used to model and predict some thermodynamic and thermo-mechanical properties of high-temperature ceramics for EBCs, although these calculations are challenging due to their high computational costs. In this work, we use machine learning to train a deep neural network potential (DNP) for Y2Si2O7, which is then applied to calculate the thermodynamic and thermo-mechanical properties at near-DFT accuracy much faster and using less computational resources than DFT. We use this DNP to predict the phonon-based thermodynamic properties of Y2Si2O7 with good agreement to DFT and experiments. We also utilize the DNP to calculate the anisotropic, lattice direction-dependent coefficients of thermal expansion (CTEs) for Y2Si2O7. Molecular dynamics trajectories using the DNP correctly demonstrate the accurate prediction of the anisotropy of the CTE in good agreement with the diffraction experiments. In the future, this DNP could be applied to accelerate additional property calculations for Y2Si2O7 compared to DFT or experiments.

Effect of PyC/BN interfacial phases on mechanical behavior of SiC/SiC composites

AbstractPyC/BN multiphase interfacial phases were prepared on the surface of SiC fiber preform, then the near stoichiometric ratio SiC fiber reinforced SiC ceramic matrix composites were obtained by polymer impregnation and pyrolysis (PIP) process. The mechanical behavior of SiC/SiC composites was characterized by three‐point bending tests and fracture toughness tests. The stress release and load transfer effects of the interfaces under external loads were analyzed by scanning electron microscope (SEM). Results showed that with the increasing of PyC component thickness from .10 to.30 µm in the PyC/BN multiphase interfacial phases, the bending strength and fracture toughness both increased first and then decreased. The results occurred due to the competition between load transfer and stress release of the interfaces. The relatively optimized interfacial phase structure was that the thickness of the PyC interfacial phase and BN interfacial phase were .20 and.30 µm. The bending strength and fracture toughness of the optimized SiC/SiC composites reached 660.65 MPa and 29.01 MPa•m1/2. Respectively, many matrix cracks appeared in the horizontal and vertical directions, occupying almost the entire fracture section. The growth path of the matrix crack was significantly increased with many long fibers pulled out and broken, which was conducive to the strengthening and toughening of SiC/SiC composites.

Multi-scale collaborative design method for macroscopic thermal optimization and mesoscopic woven structure of hypersonic vehicle’s TOCMC leading edge

A new thermal protection design method for hypersonic vehicle’s leading edge is proposed, which can effectively reduce temperature of the leading edge without additional cooling measures. This method reduces the leading-edge’s temperature by the multi-scale collaborative design of the macroscopic thermal optimization and the mesoscopic woven structures of Three-dimensional Orthogonal Woven Ceramic Matrix Composites (TOCMC). The macroscopic thermal optimization is achieved by designing different mesoscopic woven structures in different regions to create combined heat transfer channels to dredge the heat. The combined heat transfer channel is macroscopically represented by the anisotropic thermal conductivity of TOCMC. The thermal optimization multiple linear regression model is established to optimize the heat transport channel, which predicts Theoretical Optimal Thermal Conductivity Configuration (TOTCC) in different regions to achieve the lowest leading-edge temperature. The function-oriented mesostructure design method is invented to design the corresponding mesostructure of TOCMC according to the TOTCC, which consists of universal thermal conductivity prediction formulas for TOCMC. These universal formulas are firstly derived based on the thermal resistance network method, which is verified by experiments with an error of 6.25%. The results show that the collaborative design method can effectively reduce the leading edge temperature by about 12.8% without adding cooling measures.

3D observations of room temperature capillary infiltration mechanism in SiC compacts

The melt infiltration of a liquid metal is a successful method for densifying metal and ceramic matrix composites (CMC). The reduction of residual porosity of silicon carbide composites by infiltration of molten silicon into the matrix allows to reach interesting mechanical properties. However, fluid progression within the pore network of the granular matrix is a complex phenomenon, driven by physical and thermomechanical mechanisms that are not yet fully understood. This publication focuses on the capillary impregnation at room temperature and highlights important parameters related to the physical aspect of the process. Two different model fluids (n-hexadecane and exo-dicyclopentadiene) were used to reproduce the behaviour of molten silicon alloy. During the infiltration, the monitoring of the infiltrated liquid weight, along with the image acquisition, was used to compare the infiltration difference between several types of samples. An innovative way to interrupt and fix liquid inside samples, based on rapid polymerization, was investigated during capillary rise experiments. The correlation between 2D observations and 3D volumes obtained by tomography outlines the existence of two different flow fronts, the surface flow front (SFF) which often have a flat shape, and a second inside the sample, the volume flow front (VFF), which shows a paraboloid shape.

High Power Laser Cutting of SiC-Al2O3 Ceramic Matrix Composites

Machining composite to achieve the desired surface and sub-surface condition, whether through conventional or non-conventional techniques, presents persistent challenges due to their anisotropic thermal characteristics. These challenges escalate when dealing with ceramic matrix composites (CMC) due to their high melting and boiling temperature. This study investigates the surface and sub-surface characteristics of SiC-Al2O3 CMC laser-cut components, produced using a 2 kW quasi-continuous wave laser. The influence of laser parameters such as focal position, cutting speed, number of cutting passes, average power, and assist gas type on surface and sub-surface characteristics have been investigated in detail. The laser cut samples were analysed using white light interferometer, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and 3D X-ray Computer Tomography (XCT) for both surface and sub-surface characteristics. The effect of laser process parameters on the surface composition, surface topology, and sub-surface thermal defects have been studied in detail. The results revealed that multi-pass cutting (16 pass) can be used to achieve lower thermal affected zone (~200 µm) and reduced surface roughness with an overall cutting speed of 625 mm/min. No delamination was observed with multi-pass cutting. Nitrogen was found to be the most suitable assist gas, as it prevented oxide layer formation across the laser cut SiC-Al2O3 CMC surface.

Seeding ductile nanophase in ceramic grains.

Transgranular brittle fracture is the dominant failure mode of brittle materials, including ceramics and ceramic matrix composites. However, strengthening these materials without sacrificing their toughness has been a big challenge. In this study, an innovative approach is proposed to achieve coordinated strengthening and toughening of ceramics-based composites by introducing specific ductile coherent nanoparticles into ceramic grains. As an example, the WC-Co cemented tungsten carbides were used to demonstrate how this brittle material can achieve ultrahigh strength without losing toughness by seeding metallic nanoparticles inside WC grains. The mechanisms for inducing the formation and modulating the amount, size, and distribution of such nanophase within the ceramic grains were disclosed. The fraction of transgranular ruptures of the brittle ceramic phase was reduced significantly due to the presence of the ductile coherent in-grain nanoparticles. Both the strength and strain limit of the cemented carbides were remarkably increased compared to their counterparts reported in the literature. The coordinated strengthening and toughening strategy proposed in this work is applicable to a broad range of ceramics and ceramic matrix composites to obtain superior comprehensive mechanical properties.

Advanced Thermal/Environmental Barrier Coatings of High-Entropy Rare Earth Disilicates Tuned by Strong Anharmonicity of Eu2Si2O7

Advancing thermal/environmental barrier coating (TEBC) materials with integrated thermal-mechanical functions is paramount for safeguarding SiC-based ceramic matrix composites (CMCs) in high-efficiency gas turbines. Herein, we employ a synergistic approach, combining...

Research Progress on In-situ Monitoring of Damage Behavior of SiCf/SiC Ceramic Matrix Composites at High Temperature Environments

Research Progress on <i>In-situ</i> Monitoring of Damage Behavior of SiC_f/SiC Ceramic Matrix Composites at High Temperature Environments

Microwave absorption properties of PDCs-SiC(N) based on heat treatment at different temperatures

Polymer-derived ceramics (PDCs) exhibit diverse microstructures and varying levels of free carbon after pyrolysis at different temperatures, resulting in distinct wave-absorbing capabilities. In this study, PCS, PSN1, and PSN2 with different free carbon concentrations were subjected to heat treatment, followed by systematic characterization of their microstructures, particularly the transformation process of free carbon. Subsequently, the dielectric constants and microwave-absorbing properties of the heat-treated PDC powders within the 2–18 GHz range were determined using the coaxial method. Finally, an analysis was conducted on the relationship between loss mechanisms and microstructure in PDCs to establish a foundation for preparing broadband wave-absorbing ceramic matrix composites.