Properties Of Ceramic Matrix Composites Research Articles

Microstructure, interfacial and mechanical properties of SiC interphase modified C/C-SiC composites prepared by reactive melt infiltration

Interfacial modification can effectively regulate the interfacial properties of ceramic matrix composites. This paper reports on the effect of SiC interphase thickness on the microstructure, interfacial and mechanical properties of C/C-SiC composites. As the SiC interphase thickness increased to 2 μm, the flexural strength and modulus of the C/C-SiC composites increased up to 252MPa and 40GPa, an increase of 36% and 40%, respectively. Because the SiC interphase protected the carbon fibers from the corrosion of liquid silicon, thereby increasing the effective fiber volume fraction. Furthermore, the increased interfacial shear strength (IFSS) measured by the fiber push-in test improved the load transfer efficiency. Raman spectrum and transmission electron microscopy indicated that the damage process of the interface with high IFSS after the fiber push-in test showed fiber/pyrolytic carbon interface debonding, release of thermal residual stress, and larger upward rebound protrusion of carbon fibers without interface crushing.

The fiber structure evolution and performance changes of SiC–ZrC fibers after 1600 °C heat treatment

SiC fibers play an essential role in determining the mechanical properties of ceramic matrix composites. This study examines the influence of different heat treatment atmospheres at 1600 °C on the microstructural and mechanical behaviors of SiC–ZrC fibers. Experimental results demonstrate a general decline in the fibers' mechanical performance, with a reduction of 31.49% in a vacuum environment and 39.36% in an argon atmosphere. Under vacuum conditions, the amorphous phase within the fiber decomposed, leading to an increased crystallinity; however, no significant clustering of the ZrC phase was observed. In contrast, under argon conditions, the amorphous phase of SiC–ZrC underwent decomposition, accompanied by the clustering of ZrC particles, resulting in the fiber exhibiting inferior mechanical properties compared to those treated in a vacuum. In summary, doping ZrC in the fibers enhances microstructural stability under vacuum conditions, suppressing the decomposition of the SiCxOy phase. However, post heat-treatment in an argon environment led to ZrC clustering, adversely impacting the fiber's mechanical performance.

Boosting the Ceramics with In Situ MOF-Derived Nanocarbons

Metal–organic framework (MOF)-derived nanocarbons have emerged as promising materials for energy and environmental applications owing to their high surface area, structural and chemical tunability, and hierarchical porosity. Although various carbon-based materials such as graphene and carbon nanotubes have been extensively used as secondary sintering additives to develop advanced ceramics with improved mechanical, thermal, and electrical properties, the potential of MOF-derived nanocarbon-based materials has not been explored. Here, we report the first use of MOF-derived nanocarbons as a reinforcement phase in ceramic composites. To this end, Al2O3 and zeolitic imidazolate framework (ZIF-8) are used as the ceramic matrix and nanocarbon source, respectively. The ceramic composites are produced by densifying Al2O3 and ZIF-8 powder mixtures using spark plasma sintering (SPS) at 1550 °C and uniaxial pressure of 50 MPa. The fracture toughness of the composite increases up to 67% in comparison to an alumina monolith as ZIF-derived nanocarbons form interlayers to assist the dissipation of energy during the crack propagation and inhibit grain growth. The room-temperature electrical conductivity of the sintered samples drastically increases with the in situ formed nanocarbon-based fillers, reaching as high as 1410 S/m for 10 wt % ZIF-8 content. These results constitute an excellent initial step toward boosting the mechanical and electrical properties of ceramic matrix composites with in situ MOF-derived nanocarbons.

High-fidelity micromechanical modeling of the effects of defects on damage and creep behavior in single tow ceramic matrix composite

Despite the superior properties of ceramic matrix composites (CMCs), their fabrication process generates inevitable defects with high density that significantly influence material integrity and residual useful life. Recent efforts have focused on CMC property prediction and investigation of their different inelastic mechanisms, but very limited work exists on understanding the influence of defects on inelastic responses of CMCs. Here, we introduce a three-dimensional micromechanics computational framework that includes experimentally informed material microstructure and architectural variabilities to investigate CMC response in the presence of manufacturing-induced defects. A developed microstructure generation algorithm is used to generate the representative volume elements in the micromechanics models from complex material morphology information obtained from extensive characterization studies of C/SiNC and SiC/SiNC CMCs. A fracture mechanics-informed matrix damage model is reformulated, in which the model considers the growth of porosity and microcracks in the as-received material. A progressive fiber damage model as well as Orthotropic viscoplasticity creep formulation are also utilized for the study. This methodology is implemented within the micromechanics framework to investigate the complex temperature- and time-dependent load transfer and damage mechanisms of CMCs under operation loading conditions. The developed framework explores the influence of as-received defects on the damage and creep behavior in service conditions. It also provides new insights into the effect of size, shape, distribution, and location of these defects on material response. The framework is then calibrated with unidirectional CMC minicomposite results available in the literature.

Fast Statistical Homogenization Procedure for estimation of effective properties of Ceramic Matrix Composites (CMC) with random microstructure

The modern polycrystalline composite materials have a complex internal structure consisting of different phases and interfaces with random distribution. Relevant examples are Al2O3/ZrO2, i.e. alumina/zirconia composites, widely used as structural materials with applications ranging from aerospace to bio-engineering. Depending on the phases content and on the grain size a broad range of material characteristics, among which elastic constants, can be obtained.With the aim of characterizing this class of materials, we exploit a numerical Fast Statistical Homogenization Procedure (FSHP) in order to both estimate the size of the Representative Volume Elements (RVE) and the effective elastic properties, assuming a linear elastic material behaviour.The 2-D analyses are performed considering a microstructure inspired by images of real portions of the Al2O3/ZrO2 composite obtained from a scanning electron microscope. The recent Virtual Element Method is used in combination with the FSHP approach to numerically solve boundary value problems. Different volume contents of phases are considered ranging from pure Alumina to pure zirconia. The results are useful to reliably characterize such materials in the elastic range taking into account the role played by random distribution of grains.

Fast Statistical Homogenization Procedure for estimation of eec- tive properties of Ceramic Matrix Composites (CMC) with random microstructure

Fast Statistical Homogenization Procedure for estimation of eec- tive properties of Ceramic Matrix Composites (CMC) with random microstructure

Fast Statistical Homogenization Procedure for estimation of effective properties of Ceramic Matrix Composites (CMC) with random microstructure

Fast Statistical Homogenization Procedure for estimation of effective properties of Ceramic Matrix Composites (CMC) with random microstructure

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.

Phase Composition and Properties of Ceramic Matrix Composites with the Addition of Ferrovanadium Slag

Phase Composition and Properties of Ceramic Matrix Composites with the Addition of Ferrovanadium Slag

Effect of strain rate on the tensile properties of mini-SiC/SiC composites

SiC/SiC composites are the ideal candidates for hot-end components in aerospace and other high-tech fields. In recent years, as one type of material with simple structures, mini-composites have been widely used to study or initially verify the properties of ceramic matrix composites (CMC). Nevertheless, attentions were rarely paid on the influence of strain rate on the mechanical properties of mini-composites . In this study, based on mini-SiC/SiC composites, we investigated the effect of the strain rate on their tensile strength, initial tensile modulus, Weibull modulus, and fracture work. Furthermore, the underlying mechanisms were discussed and the exact constitutive model of the as-prepared mini-SiC/SiC composites was constructed according to the Michaelis-Menten and generalized linear models. This work can fill the gaps in the CMC research in some degree and provide a preliminary theoretical basis for the formulation of tensile properties test standards of mini-composites.

Microstructural features and electromechanical characteristics of ceramic-matrix piezocomposites

In this work, we studied elastic and electromechanical characteristics and microstructural features of piezoactive ceramic-matrix composites PZT/LiNbO3 with a volume fraction of microcrystalline LiNbO3 filler from 0 to 15 vol. %. The dependences of the complex elastic and electromechanical parameters of composite piezoelectric elements on LiNbO3 microcrystals concentration were measured. It was found that in the formation of the electrophysical properties of ceramic-matrix composites PZT/LiNbO3, the microporosity of the piezoceramic matrix appearing during the composite sintering played a decisive role.

Multiscale characterization and representation of variability in ceramic matrix composites

Low density, high strength, and high creep and oxidation resistance properties of ceramic matrix composites (CMCs) make them an ideal choice for use in extreme environments in space and military applications. This paper presents a detailed characterization study of structural and manufacturing flaws in Carbon fiber Silicon-Carbide-Nitride matrix (C/SiNC) CMCs at different length-scales. Energy-dispersive spectroscopy (EDS) is used for the chemical characterization of the material’s elemental constituents. High-resolution multiscale graphs obtained from scanning electron microscope (SEM) and confocal laser scanning microscope (LSM) are used to characterize the distribution and morphology of defects at different length scales. This is followed by the classification and quantification of the common manufacturing defects. An image processing algorithm based on the image segmentation process is developed to quantify the variability of various scale-dependent architectural parameters. Finally, a three-dimensional stochastic representative volume element (SRVE) generation algorithm is developed to provide precise representations of material textures at multiple length scales. The developed algorithm accurately accounts for material features and flaws based on a range of multiscale structural and defects characterization results.

Residual stress variation in SiCf/SiC composite during heat treatment and its effects on mechanical behavior

Residual stress originated from thermal expansion mismatch determines the mechanical properties of ceramic matrix composites (CMCs). Here, continuous SiC fiber reinforced SiC matrix (SiCf/SiC) composites were fabricated by nano-infiltration and transient eutectic-phase (NITE) method, and the residual stress of the composites was investigated using high-temperature Raman spectrometer. With temperature increasing from room temperature to 1400 °C, the residual stresses of the matrix and the fiber decrease from 1.29 to 0.62 GPa and from 0.84 to 0.55 GPa in compression respectively, while that of the interphase decreases from 0.16 to 0.10 GPa in tension. The variation of residual stress shows little effect on the tensile strength of the composites, while causes a slight decrease in the tensile strain. The suppression of fiber/matrix debonding and fiber pulling-out caused by the residual stress reduction in the interphase is responsible for the decreasing tensile strain. This work can open up new alternatives for residual stress analysis in CMCs.

Research on the interface properties and strengthening–toughening mechanism of nanocarbon-toughened ceramic matrix composites

Abstract Nanocarbon materials (carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, etc.) are considered the ideal toughening phase of ceramic matrix composites because of their unique structures and excellent properties. The strengthening and toughening effect of nanocarbon is attributed to several factors, such as their dispersibility in the matrix, interfacial bonding state with the matrix, and structural alteration. In this paper, the development state of nanocarbon-toughened ceramic matrix composites is reviewed based on the preparation methods and basic properties of nanocarbon-reinforced ceramic matrix composites. The assessment is implemented in terms of the influence of the interface bonding condition on the basic properties of ceramic matrix composites and the methods used to improve the interface bonding. Furthermore, the strengthening and toughening mechanisms of nanocarbon-toughened ceramic matrix composites are considered. Moreover, the key problems and perspectives of research work relating to nanocarbon-toughened ceramic matrix composites are highlighted.

Mechanical Characterisation of Carbon-Silica Reinforced Composites for Turbine Application

Materials selection and development for application in advanced systems is becoming highly complex involving the need for lower cost alternatives without compromising service performance. This paper investigated selected critical mechanical properties of ceramic matrix composites synthesized from coconut shell carbon (CSC) reinforced with silica particles (SP). Coconut shells (CCS) and silica sand (SS) were pulverized separately in a plate mill and a ball mill respectively to obtain a particle size of 250 μm. The CCS powders were calcined at 5000 C in an oven to obtain coconut shell ash (CSA) which was carbonized in a furnace from 5000 C-10000 C under argon gas controlled environment. The materials were mechanically blended while the SP additions varied from 10-40 wt. % and compacted using hydraulic press. The compacted mixture was sintered at 5000 C-12000 C, held for 2 hrs and the composites characterised for mechanical properties while the microstructural integrity was analysed using scanning electron microscope/energy dispersive x-ray spectroscopy (SEM/EDS). Microstructure showed that after sintering, coconut shell carbon developed strong cohesion with the silica particles which gave rise to effective load transfer. The mechanical properties that ensued demonstrated on the average 52.8 % comparability with conventional power plant structural materials in terms of hardness, compressive strength and impact energy.

Effect of interface strength on the mechanical behaviour of bio-inspired composites: A molecular dynamics study

Nanoscale composites inspired from biological materials such as nacre and bone are excellent candidates for improving the mechanical properties of ceramic matrix composites (CMC) or in general any brittle-matrix composites. These composites are based on the regularly staggered model (RSM) and on the stair-wise staggered model (SSM), and consist of stiffer platelets embedded in a compliant matrix. The interface between the platelets and the matrix plays a key role as an enormous amount of interfacial area exists in the nanocomposite materials. We investigate the influence of interface strength on the overall mechanical properties and deformation mechanisms of bio-inspired brittle-matrix nanocomposites. Atomistic simulations are used for this purpose and the interface strength is controlled by varying the binding energy between the platelet atoms and the matrix atoms. We found that the mechanical properties of both models initially increase with the interface strength. However, above a critical value, the trend changes drastically between the two models. The RSM model continues to maintain the flow stress and toughness at higher interface strengths, due to the persistence of deformation mechanisms such as bulk matrix plasticity and platelet pullout. In contrast, in the SSM model the flow stress and toughness are deteriorated as softening of stress and fracturing of platelets occur at higher interface strengths. The knowledge gained from this study paves new way for the development of bio-inspired ceramic-matrix composites with improved mechanical properties.

Robust reconstruction of the catalytic properties of thermal protection materials from sparse high-enthalpy facility experimental data

Quantifying the catalytic properties of reusable thermal protection system materials is essential for the design of atmospheric entry vehicles. Their properties quantify the recombination of oxygen and nitrogen atoms into molecules, and allow for accurate computation of the heat flux to the spacecraft. Their rebuilding from ground test data, however, is not straightforward and subject to uncertainties. We propose a fully Bayesian approach to reconstruct the catalytic properties of ceramic matrix composites from sparse high-enthalpy facility experimental data with uncertainty estimates. The results are compared to those obtained by means of an alternative reconstruction procedure, where the experimental measurements are also treated as random variables but propagated through a deterministic solver. For the testing conditions presented in this work, the contribution to the measured heat flux of the molecular recombination is negligible. Therefore, the material catalytic property cannot be estimated precisely. Moreover, epistemic uncertainties are rigorously included, such as the unknown reference calorimeter catalytic property.

Effect of microstructural features and properties of constituents on the thermo-elastic properties of ceramic matrix composites

It is proposed that the effect of microstructural features and constituents on thermo-elastic properties in ceramic matrix composites (CMCs) can be identified by using descriptive modeling tools. In this work, three CMC materials – N720/AS, SiC/SiNC and SiC/SiC-B4C, were modeled and tested. A hybrid FEA code was used to calculate thermo-elastic properties as a function of porosity, constituent volume fraction, and fiber coating thickness. Model inputs were obtained from properties of as-manufactured composite constituents (when possible), literature values of constituent materials, and quantitative microscopy. The results illustrate the sensitivity of the composites' physical properties to the microstructural features of interest and demonstrate a way of using modeling tools when critical input values are not available.

Study on the Preparation of SiC Coating by Chemical Vapor Phase and the Mechanical Properties of Ceramic Matrix Composites

In view of the oxidization-prone feature of C/C composites at high temperature, the effect of SiC ceramic coating on the structure and performance of the composites and the oxidation resistance of new nano-carbon particles/ silicon carbide ceramics are explored. The results show that the chemical vapor phase method applied in preparing SiC coated C/C composites can produce good coatings, which is large in coating thickness, uniform in distribution and good in combination with the matrix. The average bending strength of the SiC coated material is 40.4% higher than that of the original material, and the average maximum fracture displacement is increased by 9.26%. The vapor permeation and the enhanced interaction between SiC particles during the preparation of the SiC coating lead to the improvement of strength of the coated samples. After the coating, the fracture mode of the original material does not change fundamentally with the phenomena including interlayer debonding and fiber removal still occurring at the time of fracture, showing good damage resistance and pseudoplastic fracture characteristics. The oxidation process of the new Cp/SiC composite ceramics at 400-700°C is mainly controlled by C-O2 reaction, where the apparent porosity of Cp/SiC increases and the bending strength decreases. At 700-1100 °C, the SiC on the surface of the material is oxidized into SiO2 protective film with the apparent porosity decreased and the bending strength increased. The content of nano-carbon is the key factor affecting the strength and the complexity of oxidation of Cp/SiC composite ceramics. The SiC composite ceramics with 15% of nano-carbon has excellent oxidation resistance.

Weak interface dominated high temperature fracture strength of carbon fiber reinforced mullite matrix composites

Weak fiber/matrix interface dominates the toughening properties of ceramic matrix composites. This paper reports a novel sol-gel fabricated carbon fiber reinforced mullite matrix composite, in which the fiber/matrix interface was inherently weak in shear properties (∼25MPa), measured in-situ by fiber push-in tests. The interface microstructure was chemically sharp, characterized by transmission electron microscopy. The outcome of the weak interface was the full trigger of the toughening mechanisms like crack deflection, etc., leading to significant enhancement of the fracture toughness of the composite (∼12MPa√m), measured by single edged notch beam method. Finally, due to the weak fiber/matrix interface and large thermal expansion mismatch of the fiber and matrix, the high temperature fracture strength was enhanced in the temperature range from 25 to 1200°C, which is attributed to the enhancement of the interfacial property at elevated temperatures that favors better load transfers between composite constituents.