SiC Ceramic Matrix Research Articles

Enhancement mechanism of adhesion strength and mechanical properties of 6H-SiC ceramic matrix composites by graphene

Graphene as a reinforcing phase improves the mechanical properties of ceramic composites. However, an insufficient understanding of graphene on reinforcement mechanisms limits the application of SiC ceramic matrix composite. In the present work, the adhesion work, Mulliken population, and electronic structure of the graphene/6H-SiC (0001) interface are analyzed at the electronic level. The results show that C-I-terminated and Si-II-terminated interfaces have strong bonding strength due to the formation of the typical covalent bond at the interface. Moreover, the combination of strong and weak interfaces could adjust the fracture toughness and adhesion strength of composites. The strong bonding interface with covalent bonds can cause cracks to be deflected and bridged due to the large consumption of fracture energy, while the formation of the weak bonding interface makes the graphene easy to pull out. The present work is of great significance to expand the application range of SiC ceramic composites.

Experimental study and numerical simulation of tribological and mechanical properties of mullite and SiC ceramic matrix composite for journal bearing

This study presents a detailed analysis of mullite and SiC based ceramic matrix composites in comparison to traditional materials used in journal bearings. The research integrates experimental investigations and numerical simulations to analyze the tribological behavior and mechanical properties of these composites. The experimental analysis evaluates the frictional characteristics, wear resistance, microhardness, and thermal stability of mullite and SiC-based composites under conditions relevant to journal bearing applications, comparing them with traditional materials such as Bronze and Babbitt. Results show that the mullite-SiC composites demonstrate a lower friction coefficient of 0.15 and a wear rate of 0.002 g, significantly outperforming the traditional materials. To further understand the material behavior, computational models using finite element analysis simulated the stress distribution, deformation, and frictional characteristics at the bearing interface under varying operational parameters. It predicted no deformation in mullite-SiC composites after two hours of operation, with minimal deformation of 4.6191 mm observed after three hours. Stress analysis revealed uniform stress distribution across the composite, with a maximum stress of 2.93 MPa. Additionally, microstructural analysis using Scanning Electron Microscopy (SEM) identifies minimal abrasive wear and the absence of severe adhesive wear on the composite's surface. The average surface roughness along the wear surface was measured at 2.35 µm. Ultimately, the research outcomes aim to contribute significantly to the advancement of journal bearing technology, facilitating their application in diverse industrial settings where high performance and reliability are crucial requirements.

Tailoring structural and mechanical properties of Cf/SiC ceramic matrix composites with BN/SiAlC interphases

In this work, we studied the effects of protective boron nitride/silconaluminocarbide (BN/SiAlC) interphases on the structural and mechanical properties of fabricated stacked carbon fiber-reinforced SiC ceramic matrix composites (Cf/SiC CMCs) via the hot-press sintering route. The structural analyses were carried out by X-ray diffraction and scanning electron microscopy (SEM), while mechanical properties were elucidated by employing universal testing machine. The observed sharp diffraction peaks indicate excellent crystallization, and the formation of 4H-SiC polytype was attributed to the partial transition of β-SiC phase during high-temperature sintering. The composite with single BN interface layer revealed enhanced bending strength of up to 364 ± 39.46 MPa (↑40 %), while composite with double layered interface showed optimal strength of 436 ± 33.54 MPa, and toughness of 6.11 ± 0.74 MPa.m1/2, with increments of 67.7 % and 128.8 %, respectively, compared to the composite without interphase layer. In the composite with duplex interfacial layer (3BN/SiAlC), the microcracks generated during fracture propagated into the BN layer, deflected through both the sublayers and at the fiber-BN interface, resulting in fiber pull out using fracture energy, leading to the enhanced strength and toughness of the composite. The load-displacement curve revealed that the stacking Cf/SiC CMCs with weak interlayer binding owing to the BN/SiAlC coating treatment possesses significant toughness to the SiC ceramics.

Preparation of enhanced erosive wear resistance SiC-fiber-reinforced SiC ceramic matrix composites integrated with a knit fabric via high temperature crystallization of amorphous Si–C–O–Al fibers

We report the enhanced erosive wear resistance of SiC/SiC CMCs that were integrated with a knit fabric via high-temperature crystallization of relatively inexpensive first-generation (amorphous) fibers of Si–C–O–Al (AM; short for Tyranno™ AM) for use as sliding components. A pyrocarbon (PyC) interface was formed via dip coating in liquid phenolic resin, and matrix densification was achieved by hot pressing at 1900 °C for 1 h at 30 MPa. The PyC-coated AM fibers exhibited low tensile strength values at temperatures below 1600 °C, which increased significantly at 1900 °C (2.68 ± 0.74 GPa). The hot-pressed AM-SiC/SiC CMCs exhibited typical quasi-ductile fracture in a three-point bending test. The erosive wear of the CMCs was investigated using a slurry erosion test, and the associated mechanism was clarified by laser-microscopy-based 3D profiling and scanning-electron-microscopy-based microstructural examination. The matrix of the hot-pressed AM-SiC/SiC CMCs was dense (1.99% porosity), rigidly structured, and hard (27.1 ± 2.91 GPa), enabling the CMCs to outperform conventional SiC/SiC CMCs in terms of slurry erosion resistance.

Low viscosity high stability silicon carbide slurry for densification of SiC ceramic matrix composites

Slurry infiltration method has been widely used as a preliminary step in preparing dense and multifunctional fiber reinforced SiC ceramic matrix composites. However, the infiltration efficiency of slurry is low mainly due to its insufficient stability, specifically manifested as the limited weight gain of composite after slurry infiltration. The aim of this study is to improve the infiltration efficiency of slurry by improving its stability, while maintaining its low viscosity and high particle concentration. In this study, by adjusting the particle size, two SiC slurries with identical high particle concentration (50 wt.%) and similar low viscosities (less than 10 mPa·s) but different stabilities were obtained and then applied in the infiltration process of composites. The stability of slurry can be highly improved by decreasing the particle size. The weight gain of composites after infiltration of high stability slurry (sedimentation time exceeding 35 hours) is more than twice that of low stability slurry (sedimentation time nearly 1 hour). Combined with chemical vapor infiltration method, the final composite using high stability slurry exhibits increased density, reduced porosity and enhanced mechanical performance.

A high‐entropy (Er0.25Y0.25Ho0.25Yb0.25)2Si2O7 ceramic with good thermal properties and water‐vapor corrosion resistance

AbstractA high‐entropy rare‐earth disilicate (Er0.25Y0.25Ho0.25Yb0.25)2Si2O7 (hereinafter referred to as (EYHY)2Si2O7) ceramic was synthesized by a heat treatment process combined with spark plasma sintering. According to the experimental results, (EYHY)2Si2O7 presents good phase stability and low thermal conductivity ([1.48–2.35] W∙m−1∙K−1) from room temperature to 1200°C. Its coefficient of thermal expansion is (3.89–5.32) × 10−6 K−1 from 200 to 1400°C, similar to SiC‐based materials ([4.5–5.5] × 10−6 K−1). Due to the multiple doping effects, (EYHY)2Si2O7 exhibits outstanding corrosion resistance performance in water‐vapor corrosion tests. Its weight loss is 1.79 mg/cm2 after corrosion at 1600°C for 30 h in the presence of 50% H2O‐50% O2, which is lower than the corresponding four single components Re2Si2O7 (Er2Si2O7, Y2Si2O7, Ho2Si2O7, and Yb2Si2O7) under the same conditions. Therefore, high‐entropy (EYHY)2Si2O7 ceramics are regarded as potential environmental barrier coatings materials for SiC ceramic matrix composites.

Thermal cycling and steam corrosion behavior of Yb3Al5O12‐based multilayered environmental barrier coatings for SiCf/SiC

AbstractTo alleviate thermal mismatch problem of environmental barrier coatings (EBCs) on SiC fiber‐reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) surface and improve their high‐temperature durability for aircraft engines, by fully utilizing the appropriate thermal expansion coefficient, low oxygen transmittance, low thermal conductivity, and other advantages of ytterbium aluminum garnet (Yb3Al5O12), the double ceramic layered Yb3Al5O12/Yb2Si2O7 (DCL‐Yb3Al5O12) and the triple ceramic layered Yb3Al5O12/Yb2SiO5/Yb2Si2O7 (TCL‐Yb3Al5O12) EBC systems were prepared on SiCf/SiC CMCs by atmospheric plasma spraying (APS). Their phase composition and microstructures were investigated comparatively. The thermal cycling and water vapor/oxygen corrosion behavior of these coating systems were compared at 1300°C. The results showed that the thermal cycling life of the DCL‐Yb3Al5O12 and TCL‐Yb3Al5O12 EBC systems were 295 and 320 times, respectively. The failure of both the coating systems occurred between the Yb2Si2O7 layer and Si bond coat. The strength retention rate of DCL‐Yb3Al5O12 and TCL‐Yb3Al5O12 EBC systems after water vapor/oxygen corrosion for 70 h was 12.8% and 23.1%, respectively, and the fracture modes of both the systems exhibited “pseudoplastic” characteristic. TCL‐Yb3Al5O12 EBC systems with a gradient structure of more layers exhibit more excellent high‐temperature durability than DCL‐Yb3Al5O12 EBCs.

Slurry material extrusion of chopped carbon fiber reinforced silicon carbide ceramic matrix composites (CMCs)

AbstractSilicon carbide (SiC) is a useful high temperature ceramic due to its excellent mechanical properties and oxidation resistance. In this study, monolithic SiC and chopped carbon fiber reinforced (Cf)/SiC ceramic matrix composites (CMCs) were additively manufactured via direct ink writing (DIW). Samples employing five different print paths were prepared from SiC and 10 vol.% Cf/SiC inks. All parts were pressurelessly sintered, with relative densities of 96% measured for samples prepared from both inks. Electron and optical microscopy were used to show a high degree of fiber alignment parallel to the direction of the print. Thus, CMC architectures consistent with the print paths were created when printing the 10 vol.% Cf/SiC inks. Characteristic flexure strengths for monolithic SiC and 10 vol.% Cf/SiC CMC samples were the same for the 0° print path, measuring 360–375 MPa. Fiber pullout was observed on the fracture surface of the 10 vol.% Cf/SiC CMCs. The Weibull modulus for the 10 vol.% Cf/SiC CMC samples (10.7) was greater than the monolithic SiC samples (7.4); the trend of fibers narrowing the distribution of failure strengths was consistent for the other print paths investigated.

High performance Csf/SiC ceramic matrix composites fabricated by material extrusion 3D printing and precursor infiltration and pyrolysis

Material extrusion (ME) 3D printing is an emerging technology to fabricate short carbon fiber reinforced SiC ceramic matrix composites (Csf/SiC CMCs) with highly oriented short carbon fibers. In this study, the Csf/SiC CMCs were fabricated by ME 3D printing combined with the following precursor infiltration and pyrolysis (PIP). The short carbon fibers could be well kept after the PIP process. The effects of solid loading and fiber content on the microstructure and mechanical properties of the Csf/SiC CMCs were also investigated. Higher solid loading was beneficial for obtaining the denser Csf/SiC CMCs with more oriented fibers. The introduction of short carbon fibers brought more pores. The bending strength and fracture toughness of Csf/SiC CMCs first increased and then decreased with the increase in fiber content. The pulling-out and breakage of short carbon fibers contributed to the improvement of mechanical properties. High performance Csf/SiC CMCs with a bending strength of 212.74 MPa and fracture toughness of 5.84 MPa m1/2 were simultaneously achieved when the solid content was 50 vol% and the fiber content was 20 vol%. It is believed that this study can provide some understanding of the 3D printing of fiber reinforced CMCs.

Hoop tensile properties of SiC fiber-reinforced SiC matrix composite tubes with/without CVD-SiC coating

Continuous SiC fiber-reinforced SiC ceramic matrix (SiCf/SiC) composite tubes with/without external CVD-SiC coating were mechanically tested with a C-ring sample geometry. The hoop tensile strength of the tubes with the coating (∼169 MPa) was higher than those without coating (∼108 MPa). SEM observation showed the propagation of cracks in SiCf/SiC composite materials led to the debonding of fibers from the matrix and resulted in the delamination of fiber bundles. The propagation direction of the crack initiated in the CVD-SiC coating moved toward the center of the C-ring, deflected and extended along the boundary between the coating and SiCf/SiC composite. The CVD-SiC coating and the interface between the coating and SiCf/SiC composite could effectively protect the SiCf/SiC composite, thereby improving the hoop tensile strength and maintaining the integrity of the cladding tube.

Mechanical properties and tensile failure behavior of SiCnf/SiC composites with multilayer interphases

SiC fiber-reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) hold potential as thermal structural materials. In this work, SiC nanofibres were coated with multilayer interfaces by magnetron sputtering with the aim to tailor the fiber-matrix interface of SiC nanofibre reinforced SiC composites for superior mechanical properties. The influence of multilayer interface coating and sintering temperature on the density, microstructure, and mechanical properties of SiCnf/SiC CMCs fabricated via a hot-press technique employing ultra-long single-crystal SiC nanofibers as reinforcement were investigated. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and a universal testing machine. The prepared CMCs were toughened and strengthened by the observed fiber pull-out and bridging. The multilayered SiCnf/SiC CMCs with multiple interface coatings display an identifiable saw-tooth-like pattern in the load-displacement test, suggesting a significant improvement in the toughness of prepared materials through a laminated structure with weaker interface binding brought on by the thicker, denser coating. In comparison to the SiCnf/SiC composites without interface coating, the prepared SiCnf/SiC CMCs with PyC/SiAlC/ZrC interface layers revealed optimum flexural strength (520 ± 28.88 MPa, ↑46.5 %) and fracture toughness (9.95 ± 0.44 MPa m1/2, ↑94.7 %) after an hour of hot pressing at 1800 °C under pressure of 30 MPa. Besides an increase in relative density at high sintering temperatures (1850 °C), further grain coarsening deteriorated mechanical properties.

Microstructure and mechanical properties of multilayer SiC nanofiber paper‐reinforced SiC composites by the NITE method

AbstractIn this work, stacked SiC fibers paper‐reinforced SiC ceramic matrix composites (SiCnf/SiC CMCs) were prepared by nanoimpregnation and transient eutectic (NITE) process using ultra‐long single‐crystal SiC nanofibers. The effect of the SiCnf surface modification via boron nitride (BN) interphase deposition as well as the sintering additive (Al2O3–Y2O3) content on the density, microstructure, and mechanical properties of SiCnf/SiC CMCs has been investigated systematically. The results revealed that the laminated SiCnf/SiC CMCs feature a significant saw‐tooth‐like curve on the load–displacement test, which indicates that the obtained laminated structure with the weak interlayer binding owning to the BN coating treatment possesses significant toughening to the SiC ceramics. Specifically, the SiCnf/SiC CMCs with the sintering additive content of 12 wt% revealed a fracture toughness of over 10 MPa m1/2 after 60 min of BN interface deposition, which is 104.31% higher than that of the composites prepared without BN coating.

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.

Al2O3 fiber-reinforced MAX phase ceramic matrix composite

In the aerospace industry, lightweight can reduce the weight of the engine and improve the thrust-weight ratio of the engine. Ceramic matrix composites have attracted widespread attention in the industry due to their much lower density compared to high-temperature alloys and excellent high-temperature performance. SiC fiber-reinforced SiC ceramic matrix composites are the most outstanding representatives, but their long manufacturing cycle and high manufacturing costs limit their widespread use. Ti2AlC is a new type of ceramic material with the characteristics of low density, high melting point, high-temperature resistance, oxidation resistance, and corrosion resistance of ceramic materials, as well as the conductivity and machinability of metals. However, its mechanical properties are slightly inadequate. The use of chopped fibers for toughening can compensate for these deficiencies to a certain extent and improve mechanical properties. This article first explored the influence of various process parameters on the mechanical properties of pure-phase Ti2AlC ceramic materials in SPS preparation technology and then prepared Ti2AlC composites reinforced with 10 vol%, 20 vol%, and 30 vol% Al2O3 chopped fibers. The results showed that the samples prepared at 1300 °C, 40 MPa, and 10 min had a flexural strength of 697 MPa and a fracture toughness of 9.83 MPa m1/2 when the volume ratio of the reinforcement phase was only 10 vol%, which was the same as that of the continuously fiber-reinforced SiCf/SiC composites. This study showed that the MAX phase matrix composites reinforced with chopped fibers have the potential to become high-temperature structural materials by adjusting the composite composition and optimizing the preparation process.

Influence of the thickness of pyrolytic carbon interphase on the mechanical behavior of SiC/(BN/PyC)/SiC composites

The composition and thickness of the interphase are critical factors affecting the strength of SiC/SiC materials. Therefore, SiC/(BN/PyC)/SiC ceramic matrix composites with varying PyC thicknesses were fabricated, and the mechanism by which thickness influences the mechanical properties of the materials was investigated. During the fracture process of the composites, debonding and crack deflection predominantly occurred at the BN/PyC interface. The PyC interphase thickness emerged as a critical factor influencing the mechanical performance of composites. The residual stresses within the PyC and its adjacent SiC matrix were determined by analyzing shifts in Raman peak positions. The findings indicate that a reduction in PyC thickness leads to an increase in residual compressive stress within the PyC and a corresponding increase in residual tensile stress within the SiC matrix, which increases the interfacial shear stress and improves the mechanical properties of the composites.

Mechanical properties and microstructure evolution of KD‐SA SiCf/BN/SiC CMCs oxidized at different temperatures

AbstractSilicon carbide fiber‐reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) based on a domestic KD‐SA SiC fiber were exposed to a wet oxygen atmosphere for 135 h at 800, 1100, and 1300°C. The evolution of the microstructure and mechanical properties of SiCf/SiC CMCs have been systematically investigated following oxidation. For weight change, CMC‐1300 showed the greatest gain (0.394%), followed by CMC‐1100 (0.356%) and CMC‐800 (0.149%). The volatilization of boron oxide (B2O3) combined with the slight oxidation of the SiC matrix at 800°C caused crack deflection and fiber pull‐out. The complete dissipation of the interphase could be found when the oxidation temperature increases to 1100°C, generated a fracture surface with brittle fracture characteristics. At 1300°C, crystalline SiO2 hindered oxygen diffusion, with evidence of fiber pull‐out. Based on thermodynamic calculations and microscopic observations, we propose a mechanism to explain the thermal degradation of SiCf/SiC CMCs. This work offers valuable guidance for the fabrication of SiCf/SiC CMCs that are suitable for high‐temperature applications.

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.

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.

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

Fiber-laying-assisted material extrusion additive manufacturing of continuous carbon fiber reinforced SiC ceramic matrix composites

A novel fiber-laying-assisted method for the additive manufacturing of continuous carbon fiber reinforced SiC (Cf/SiC) ceramic matrix composites was proposed. A fiber-laying-assisted material extrusion (ME) additive manufacturing system was developed to enable the introduction of continuous carbon fiber in ceramic components during the part fabrication. In this process, SiC slurry was extruded through a nozzle to build the SiC matrix layer-by-layer. In the case of continuous carbon fiber introduction, the fabrication process was halted after a certain layer was deposited; the continuous carbon fibers were placed in their predetermined locations by the fiber-laying system; and the remaining layers were deposited until the part fabrication was completed. Because the continuous carbon fibers were embedded during the fabrication process, they were fully integrated with the SiC matrix and the problems of traditional continuous fiber introduction could be eliminated. Then, the Cf/SiC green parts were densified by precursor infiltration and pyrolysis (PIP), and the final Cf/SiC composites were obtained. The effects of spacing between neighbor continuous carbon fibers on the microstructure and mechanical properties of Cf/SiC composites were also studied. When the spacing between neighbor continuous fibers was 5.0 mm, the Cf/SiC composite had a maximum bending strength of 217.16 MPa and a maximum fracture toughness of 13.55 MPa m1/2. The continuous carbon fibers improved the fracture toughness of Cf/SiC composites, which was about 3 times better than that of the SiC ceramics without fibers. This work unravels the potential of additive manufacturing of continuous carbon fibers into ceramics.