Ceramic Matrix Composite Components Research Articles

The oxidation life analysis method for SiC/SiC composite components based on an equivalent diffusion coefficient model

AbstractA method for the oxidation life analysis of SiC/SiC composite structures was proposed to predict the oxidation life of ceramic matrix composite (CMC) components. In this paper, multiscale diffusion–oxidation simulation of the CMCs’ structure can be carried out by establishing the equivalent diffusion coefficient model, to get the microscopic oxidation morphology parameters at each point. Based on the results, the residual stiffness is calculated with the homogenization method. Then, the residual stiffness is taken as the material parameter of element to calculate the stress distribution after oxidation in the CMC structure. And the residual strength of CMCs was calculated by progressive damage analysis. The oxidation life of CMC component is analyzed by judging the failure condition of each element. Finally, the oxidation life prediction of the CMC adjustment sheet under specific loading environment is realized, which is about 1 200 h. The results show that this method is feasible for the calculation of hot end parts under actual complex loads.

Investigation of the film cooling performance of ceramic matrix composites plate with different braided structures

The ceramic matrix composite (CMC) materials have been gradually applied in the high temperature components, due to its excellent heat resistance and mechanical performance. The CMC component still need cooling to protect its safe operation in the high temperature environment of aero engine, such as film cooling structure. This study focuses on the influence of braided structure on the film cooling effect over a three-dimensional braided CMC plate. The full-size calculation model reflecting the internal mesoscale structure of CMC plate was established. The thermal properties of fibers and matrix are also introduced in mesoscale. The geometric parameter which is braided angle of braided structure is changed in different models, to analyze its impacts on the comprehensive film cooling effect. The results show that the fiber bundles inside the CMC plate are the main heat transfer channel, due to its relatively higher thermal conductivity. The different braided angles affect the anisotropic thermal conductivity of CMC on the three main directions. There exists an optimal braided angle near 40° that maximizes the heat dissipation effect in the region near the film cooling holes. While in the downstream region away from holes, the influence of braided angle is weak.

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.

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.

Experimental and numerical analysis of CMCs mechanical properties under high-temperature thermal gradient environment

This paper carried out a high-temperature thermal gradient cycling test of ceramic matrix composites (CMCs), investigating the failure characteristics of CMCs in non-uniform high-temperature environments. The result shows that the damage characteristics of CMCs under thermal gradient environments are significantly different from those under uniform temperature environments. The SiC fiber pull-out lengths at different yarn fractures have obvious differences in the thermal gradient direction. The thermal stress damage propagation pattern of CMCs under the thermal gradient environment is revealed by numerical analysis, and its residual mechanical properties under different thermal gradient environments are predicted. The numerical results could be adopted as a theoretical basis and suggestions for temperature control of CMCs components in practical applications.

Physics-informed machine learning with high-throughput design module for evaluating rupture life and guiding design of oxide/oxide ceramic matrix composites

In this paper, a unified physics-informed machine learning (PIML) model is proposed for the accurate prediction of the creep rupture life of oxide/oxide ceramic matrix composites (CMCs) by incorporating prior physical information and microstructure features. The collected dataset undergoes missing value imputation and standardization methods for processing. Key feature parameters that influence rupture life are identified through global sensitivity analysis. Furthermore, a high-throughput design module is developed to explore optimal composition under specific creep conditions, providing design guidelines for new materials in oxide/oxide CMCs. This study demonstrates that the predicted results consistently fall within the ±3 error bands. Improved life expectancy is attained with fiber modulus (220–290 GPa) and matrix modulus (>310 GPa). The transformation from expensive creep testing to low-cost exploration of modulus and proportional limit is achieved, offering theoretical support and analytical methods for the design of CMC components and the development of new materials for high-temperature applications.

Modeling microvoiding kinetics of rare‐earth disilicates in flowing atmospheres containing water vapor

AbstractRare‐earth disilicate (REDS, RE2Si2O7) layers that may be used as environmental barrier coatings (EBCs) on ceramic matrix composite (CMC) components in high‐temperature stages of turbine engines are subject to microvoiding to form porous rare‐earth monosilicate (REMS, RE2SiO5) layers in flowing atmospheres containing water vapor. A simple microvoiding kinetic model that incorporates both mass transfer of the reaction product Si(OH)4(g) through the external gas phase boundary layer and pore diffusion of Si(OH)4(g) through the microvoided layer has been developed. Model predictions are in good agreement with measured growth rates of microvoided layers under low‐flowrate steam furnace test and high‐flowrate burner rig conditions. Since pore diffusion is generally the rate‐limiting step for EBC microvoiding in turbine engines, furnace testing under conditions of kinetic control by gas phase mass transfer is not generally capable of predicting REDS microvoiding rates under engine conditions. The kinetic model can be extended to incorporate changes in pore size and distribution, cracking of the microvoided layer, and introduction and cracking of an additional REMS topcoat to the system. The model can be used to generate a reasonable prediction of the time required to fully microvoid a REDS EBC layer on a CMC component in the hot gas path of an aircraft engine or stationary gas turbine.

Preparation and water-vapour corrosion behaviour of BSAS environmental barrier coatings fabricated on ceramic matrix composites

Environmental barrier coatings (EBCs) are commonly utilized to protect ceramic matrix composite components from water vapour attacks in commercial gas turbine engines. In this work, Si/3Al2O3·2SiO2 (Mullite)/BaO-SrO-Al2O3-SiO2 (BSAS) tri-layered EBCs were fabricated on SiC-based ceramic matrix composites (CMC) substrate via atmospheric plasma spraying technique. The phase composition, microstructure, and bond strength of the environmental barrier coatings were studied by scanning electron microscope, energy dispersive spectrometer, X-ray diffraction analyzer, and mechanical test machine. The water vapour resistance of the BSAS coating and CMC was evaluated with a self-assembled water-vapour corrosion test device. The results indicate that the as-sprayed BSAS coating with a porosity of (5.9 ± 0.8) % mainly comprises the monoclinic celsian BSAS phase, hexacelsian BSAS phase, and SiO2 phase. The consumption velocity of the BSAS coating is about 12 % that of the naked CMC material in a 1300 °C water vapour environment. After corrosion for 300 h, the average flexural strength of naked samples was (481 ± 9) MPa, which was about 64 % of the coated ones. In addition, the bond strength of the as-sprayed coating is (18.7 ± 1.6) MPa. Even after 300 h of water vapour corrosion, the bond strength of the coating does not decay. Evidently, BSAS coating can protect CMC materials from water vapour corrosion at 1300 °C.

Interface wear effects in ceramic composite crack opening

For fiber-reinforced ceramic-matrix composites (CMCs), crack opening behavior controls oxidation atmosphere ingress into the internal composite, which affects the operation reliability and durability of engineering CMC components. Under cyclic fatigue loading, interface wear affects the crack opening behavior in CMCs. In this paper, the stress/cyclic-dependent crack opening behavior in CMCs is analyzed considering interface wear effect. The analytical crack opening displacement (COD) and related damage parameters (e.g., interface debonding ratio (IDR)) are determined based on the microstress analysis in the fiber and the matrix. Experimental CODs of different matrix cracks in SiC/SiC minicomposite are predicted under tensile loading. Considering cyclic-dependent interface wear effect, CODs and related damage parameters are analyzed for different cycles. Theoretical relationships between the COD, peak stress level, cycle number, and composite constitutive properties are established. Effects of constitutive properties, peak stress level, and damage state on cyclic-dependent COD and related damage parameters are discussed. Under tensile loading, with increasing tensile stress, COD first increases nonlinearly and then linearly with applied stress corresponding to change of the interface debonding from partial to complete debonding. The increasing rate of COD curve is relatively low upon initial loading due to short interface debonding range. However, the increasing rate of COD curve decrease again at high stress level at the condition of complete interface debonding. Under cyclic fatigue loading, the change of interface debonding condition with increasing applied cycles affects the COD and IDR curves.

To drill or not to drill? Creep of an oxide‐oxide composite with diamond‐drilled effusion holes at elevated temperature

Ceramic matrix composites (CMCs) are prime candidates for use in aircraft engines. Yet even with their high-temperature capabilities, many CMC components will need cooling. Film cooling technique requires rows of small holes through the component surface. Effects of multiple small holes on tensile stress-strain and tensile creep performance of an oxide-oxide CMC consisting of Nextel 720 alumina-mullite fibers in a porous alumina matrix were evaluated at 1200°C. Test specimens included 17 holes with a .5 mm diameter in the gage section. The holes were precision drilled using diamond coated drill bits. The presence of diamond-drilled holes noticeably lowered tensile properties and degraded creep performance of the CMC. Our earlier study considered the effects of small holes drilled using a CO2 laser on the tensile properties and tensile creep resistance of this composite. The presence of laser-drilled holes also considerably lowered the creep resistance of the Nextel 720/alumina CMC. In both cases the reductions in tensile strength and creep resistance are due to damage caused to composite microstructure by hole drilling. However, different drilling techniques result in different microstructure degradation mechanisms. Damage to the CMC microstructure caused by these two drilling techniques and implications for mechanical performance and durability are discussed.

A novel low-damage and low-abrasive wear processing method of Cf/SiC ceramic matrix composites: Laser-induced ablation-assisted grinding

• Laser-induced ablation-assisted grinding (LIAAG) method is first proposed. • C f /SiC composites occur chemical transformation, resulting in loose SiO 2 . • Grinding force and temperature are significantly reduced with laser ablation. • Surface morphology of C f /SiC composites shows as microfracture and crushing. • Cleavage fracture of diamond grain is reduced during LIAAG. Continuous fiber-reinforced ceramic matrix composites are promising materials for advanced hot end components and safety-critical components of aeronautics and astronautics; however, the difficult-to-process problem of these materials has been one of the technical bottlenecks restricting their high-performance service. The present work proposed a novel high-efficiency, low-damage, and low-abrasive wear processing method based on the chemical properties of the materials, which used lasers to ablate workpieces before grinding—laser-induced ablation-assisted grinding (LIAAG). The material removal mechanism of C f /SiC composites was investigated by single-grain scratching tests; the grinding performances of LIAAG in terms of grinding force, grinding temperature, surface integrity, abrasive wear, grinding chips were evaluated by a contrast abrasive belt grinding test. It was found that C f /SiC composites were chemically transformed into relatively loose and homogeneous ablation products (SiO 2 and recrystallized SiC) at high laser ablation temperatures, which were easier to remove during grinding. In this case, surface morphologies displayed the microfracture and crushing of carbon fibers and SiC matrixes, and the grinding-induced damages, such as macro fracture, fiber pull-out, interface debonding, were significantly contained. Abrasive belt was primarily worn in micro-adhesion and micro-abrasion, rather than cleavage fracture and the fall-off in traditional grinding. Under optimum parameters, the grinding force, grinding temperature, and average surface roughness of belt grinding were reduced by 47 %, 40 %, and 26 %, respectively. Consequently, the surface integrity was improved greatly, and the abrasive wear was reduced significantly. The work provides a vital high-performance processing method for ceramic matrix composites components.

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

Abstract The initial mechanical response of ceramic matrix composites (CMCs) is linear until the proportional limit. This initial response is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during various phases of analysis and design of CMC components. CMCs are typically made with ceramic unidirectional (UD) or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is the polymer impregnation and pyrolysis (PIP) process. As this process involves pyrolysis to convert a preceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This volume shrinkage can lead to significant defects in the final material in the form of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, a multiscale micromechanics modeling framework is developed to study the effects of processing-induced defects on the linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length scales play an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

Accelerated oxidation during 1350°C cycling of ytterbium silicate environmental barrier coatings

AbstractEnvironmental barrier coatings (EBCs) will be needed to protect SiC‐based ceramic matrix composite components for the next generation of high‐efficiency industrial gas turbines (IGTs). The IGT application will require ≥25 kh lifetimes, and little data are available on EBC failure mechanisms, particularly at ≥1300°C. Initial 1‐h furnace cycle testing at 1350°C in 90 vol% H2O/10 vol% air was conducted ≥1000 cycles on thermally sprayed ytterbium disilicate (YbDS) coatings with and without an Si bond coating. By ≥1000 h, both EBCs formed thick, highly cracked, and fully crystalline cristobalite scales. Comparison of thermally grown oxide (TGO) microstructure and kinetics to isothermal rates of Si and SiC steam oxidation indicated a departure from slow‐growing parabolic growth to more rapid rates of silica formation. Possible mechanisms and implications for this acceleration are discussed.

Refractory eutectic assisted bonding (REABond) technology for joining of high temperature silicon carbide‐based composite materials

AbstractContinuous ceramic fiber‐reinforced ceramic composite materials are targeted for high temperature thermostructural components in aerospace. Advanced joining and integration technologies are enabling for the fabrication of large and complex shaped ceramic matrix composite components. Silicon rich refractory eutectic phase compositions in silicon‐chromium (Si‐18 at% Cr), silicon‐titanium (Si‐16 at% Ti), and silicon‐hafnium (Si‐8.5 at% Hf) systems were investigated for joining studies. The Si‐8.5 at% Hf system was down‐selected and further evaluated for joining silicon carbide fiber bonded composite (SA‐Tyrannohex) and additional fiber‐reinforced composite materials. Microstructural analysis of polished cross‐sections using optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used to evaluate the joint quality and determine the composition of the reaction formed phases. Joints along the full length of the paired substrates were observed to be well adhered, uniform, and free of gaps and pores. Single lap offset testing conducted at room temperature, 750°C, and 1200°C showed very good strengths when the fibers in the SA‐Tyrannohex material were perpendicular to the joint interface. However, when the fibers were orientated parallel to the joining plane, failures were premature due to the low interlaminar strength of the SA‐Tyrannohex material and occurred away from the joint interface.

Non‐oxide CMC fabricated by Fused Filament Fabrication (FFF)

AbstractThe present study introduces an approach to additively manufacture non‐oxidic Ceramic Matrix Composites (CMCs) by the Material Extrusion (MEX)‐based Fused Filament Fabrication. Therefore, highly SiC particle filled thermoplastic filaments were developed containing short fibers and/or long fibers to maintain shape during the thermal treatment and exhibiting flaw tolerant behavior. Polymer Infiltration and Pyrolysis (PIP) was applied to densify the microstructure. It is shown that a low content of long fibers of about 5 % can already exhibit damage tolerance comparable to steel reinforced concrete. Thus, the mechanical behavior is different to conventional fiber composites with significant higher fiber volume content. Nevertheless, these results enable new opportunities for producing advanced complex CMC components by means of Additive Manufacturing (AM).

Longitudinal amplitude effect on material removal mechanism of ultrasonic vibration-assisted milling 2.5D C/SiC composites

The anisotropic, heterogeneous, brittle and hard nature of ceramic matrix composites (CMCs) challenge machining process. Ultrasonic vibration-assisted machining may be an excellent method for processing these CMCs. The paper aims to investigate the effect of longitudinal amplitude on material removal mechanism of ultrasonic vibration-assisted milling (UVAM) 2.5D C/SiC composites. Firstly, the UVAM experiments of 2.5D C/SiC composites are performed at different longitudinal amplitudes. Secondly, the machined surface defects, surface roughness and cutting force are measured and analyzed. The UVAM experimental results show that the longitudinal amplitude of tool changes the ratio of local fragmentation fracture and abrupt macro fracture in carbon fiber removal modes to affect surface quality. Finally, a novel micro-mechanical model of UVAM carbon fiber in 2.5D C/SiC composites is proposed. The proposed model demonstrates that the longitudinal amplitude induces alternate impact load in carbon fiber and is positively correlated with alternate impact load frequency. The strain rate increases with the alternate impact load frequency, which leads to the embrittlement and local fragmentation of the carbon fiber at the stress point. On the other hand, the cutting force increases at the excessive longitudinal amplitude, which makes the carbon fiber more prone to abrupt macro fracture during machining process. A comprehensive evolution mapping of the carbon fiber fracture process is established to explain the relationship between machining process, removal mechanism, and surface defects. This work suggest that the machined quality of CMCs component can be improved by selection of optimized longitudinal amplitude by control fracture-mode percentage in UVAM.

Influence of Anisotropic Thermal Conductivity on Overall Cooling Effectiveness on a Film-Cooled Leading Edge

Abstract Increasing interest in the use of ceramic matrix composites (CMCs) for gas turbine engine hot gas path components requires a thorough examination of the thermal behavior one may expect of such components. Their highly anisotropic thermal conductivity is a substantial departure from traditional metallic components and can influence the temperature distribution in surprising ways. With the ultimate surface temperature dependent on the internal cooling scheme, including cooling from within the film cooling holes themselves, as well as the external film cooling, the relative influence of these contributions to cooling can be affected by the directionality of the thermal conductivity. Conjugate heat transfer computational simulations were performed to evaluate the effect of anisotropy in the leading edge region of a turbine component. The leading edge region is modeled as a fully film-cooled half cylinder with a flat afterbody. Changing the anisotropic directionality of the thermal conductivity is shown to have nearly the same effect on temperature distribution over the surface of the leading edge as increasing the thermal conductivity by a factor of four. While structural considerations with CMC components are often paramount, designers should be aware of the thermal ramifications associated with the selection of the CMC lay-up.

Innovative procedure for 3D printing of hybrid silicon carbide/carbon fiber nanocomposites

AbstractA novel route to fabricating hybrid ceramic matrix composites has been developed. The fabrication is based on the unique combination of additive manufacturing (AM), a preceramic polymer, and a chopped carbon fiber precursor. After introducing the photoinitiator to the preceramic polymer formulation, a photosensitive resin was introduced. The resulting resin was loaded with distinct weight percentages of stabilized polyacrylonitrile nanofiber—the carbon fiber precursor. These formulations were 3D printed, cured, and converted to ceramic phases using a pyrolysis cycle. The end objective of the pyrolysis cycle is the conversion of the polycarbosilane resin into a silicon carbide matrix and the transformation of the PAN polymer into reinforcing carbon nanofibers within one cycle. The results of this work showed that ceramic matrix composite components can be successfully fabricated using a suitable combination of 3D printing, resin formulation, and processing cycle. The pyrolyzed ceramic hybrid composite was fully dense with nearly linear shrinkage and a shiny, smooth surface. Approximately 60% retained weight after pyrolysis to 1350°C was confirmed by thermogravimetric analysis. In terms of crystallography, the ceramic matrix composite displayed three coexisting phases including silicon carbide, silicon oxycarbide, and turbostratic carbon. The results showed this combination of material and processes has a high potential for fabricating hybrid composites with high‐temperature performance and improved mechanical properties combined with complex geometries.

Machine-Learning-Based Atomistic Model Analysis on High-Temperature Compressive Creep Properties of Amorphous Silicon Carbide.

Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are used for high-temperature applications such as the hot section in turbines. For such applications, the mechanical properties at a high temperature are essential for lifetime prediction and reliability design of SiC-based CMC components. We developed an interatomic potential function based on the artificial neural network (ANN) model for silicon-carbon systems aiming at investigation of high-temperature mechanical properties of SiC materials. We confirmed that the developed ANN potential function reproduces typical material properties of the single crystals of SiC, Si, and C consistent with first-principles calculations. We also validated applicability of the developed ANN potential to a simulation of an amorphous SiC through the analysis of the radial distribution function. The developed ANN potential was applied to a series of creep test for an amorphous SiC model, focusing on the amorphous phase, which is expected to be formed in the SiC-based composites. As a result, we observed two types of creep behavior due to different atomistic mechanisms depending on the strain rate. The evaluated activation energies are lower than the experimental values in literature. This result indicates that an amorphous region can play an important role in the creep process in SiC composites.

Bending fatigue behavior in an advanced SiC/SiC ceramic matrix composite component at elevated temperature in air

The present study aims to understand the high-temperature bending fatigue behavior at the stress-concentrated Y-shape junction of a component made of Tyranno SA3 fiber/BN interphase/SiC matrix composite. The SiC/SiC CMC component was processed via a hybrid technique by combining Chemical Vapor Infiltration (CVI) and Polymer Impregnation and Pyrolysis (PIP) processes. Two different types of tests, namely, point-load-bending-static-test and point-load-bending-fatigue-test, were performed at 1100 °C. The point-load-bending-static test revealed quasi-ductile or shear failure owing to the lower elastic modulus of the PIP-SiC matrix. The first matrix-cracking occurred when the high-stress region reached approximately 180 MPa, which was facilitated by the pores and cracks that remained after the PIP process around the intricate Y-shape junction of the sample. The point-load-bending-fatigue tests were performed under the maximum of the fatigue stresses ranging from 180 to 290 MPa. When the maximum of the fatigue stress was lower than 60% of the static strength, multiple matrix-cracking were pronounced such that the component did not fail and withstand 1000 fatigue cycles. At higher stresses of 250 and 290 MPa, delamination due to shear stress generation at the fiber tows interface and degradation of the BN interphase ultimately led to the fracture of the component at low fatigue cycles of less than 100. Moreover, the fracture morphology of the 290-MPa-fatigue sample showed brittle failure, which was due to matrix-crack-assisted oxygen embrittlement. In addition, a brief comparison between the point-load-bending-fatigue test and the conventional tension-compression fatigue test was discussed.