SiC Ceramic Matrix Composites Research Articles

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.

3D microstructure characterization of 2D Cf-ZrB2-SiC ultra-high temperature ceramic matrix composites using X-ray microscopy

A study has been carried out to examine the impact of fibre architecture on the infiltration permeability, constituent phase volume fractions, and matrix porosity of the carbon fibre (Cf)-ZrB2-20 vol% SiC ceramic matrix composites prepared through slurry infiltration, followed by hand lay-up and hot pressing. Unidirectional (UD) Cf-fibres in 0/0° and 0/90° orientations, as well as 8H satin woven Cf-fibres, have been utilized as reinforcement in the composites, which were subsequently densified through hot pressing after infiltration. Revelation of the 3D internal structure of the composites by X-ray microscopy has facilitated a thorough qualitative and quantitative evaluation of infiltration. The fraction of matrix (ZrB2 - 20 vol% SiC) present along three orthogonal axes (X, Y and Z) of the scanned composite blocks has been calculated, with Z representing the direction of infiltration. This study has revealed that the composites processed from UD Cf-fibre preform exhibits greater infiltration, because of higher intra-bundle infiltration compared to the 8H woven Cf-fibre, and the accompanying analysis provides insight into the formation mechanisms of matrix porosities.

Additive manufacturing Cf/SiC composites with high fiber content by stereolithography combined with precursor infiltration and pyrolysis

A photocurable ceramic precursor slurry with a carbon fiber content of up to 25 vol% was prepared and carbon fiber reinforced SiC ceramic matrix composites (Cf/SiC composites) were successfully fabricated by stereolithography (SLA) combined with precursor infiltration and pyrolysis (PIP). The photocuring ability of the precursor composite slurry was investigated. The calculated result showed that the penetration depth of the slurry prepared with polycarbosilane (PCS) powder and chopped carbon fiber was 59.98 μm, which was suitable for stereolithography. In addition, the bulk density, porosity, flexural strength and micromorphology of the green body, debinding body and final Cf/SiC composites were analyzed in detail. After eight cycles of PIP, the bulk density and flexural strength of final Cf/SiC composites were 2.03 ± 0.04 g/cm3, 109.99 ± 15.05 MPa, respectively. This work provides a reference for additive manufacturing of Cf/SiC composites by stereolithography.

Effect of fiber orientation on tribological properties of fiber‐reinforced C/C–SiC composites mated with ceramic ball

AbstractCarbon fiber–reinforced SiC ceramic matrix composites (C/C–SiC composites) with advantages of high wear resistance and corrosion resistance are of high application potential as ceramic bearings. In this study, the frictional and wear behaviors of C/C–SiC with different fiber orientations mating with Al2O3 and SiC balls, respectively, have been investigated. Results reveal that fiber orientation effectively affects the friction and wear properties of carbon–ceramic composites in paired friction experiments with ceramic balls. In comparison to C/C–SiC with unidirectional fiber orientation, C/C–SiC pads with randomly arranged fibers exhibited a more stable coefficient of friction and lower volume wear, presenting the best performance among the pads considered herein, which may have the potential to be applied to bearing materials. The factors affecting the formation of continuous tribo‐film, which influence the comprehensive performance, are researched. It is proposed that the amount of wear debris and the formation of SiC/SiC micro‐hard frictional pairs may inhibit or promote the formation of continuous friction film. The dominant wear mechanisms for friction pairs of C/C–SiC and ceramic are abrasive wear and oxidation wear.

Matrix cracking onset stress and strain as a function of temperature, and characterisation of damage modes in SiCf/SiC ceramic matrix composites via acoustic emission

The complex damage mechanisms that accumulate within SiC f /SiC ceramic matrix composites (CMCs) subject to thermal and mechanical stress are being investigated in anticipation of the material’s introduction into high performance gas turbine engines. Acoustic emission (AE) is recognised as a leading non-destructive evaluation (NDE) tool to this end, and was used in this study to determine the so-called matrix cracking onset stress under tensile load as a function of temperature up to a maximum of 1100°C. Onset stress was interpreted using three traditional measurements based on AE energy characteristics during monotonic tests to failure. Pattern recognition (PR) analysis was performed on the AE data, revealing a specific cluster of signals that correlated closely with the initial matrix cracking region of the stress-strain curve. Taken in isolation, the onset stress of this activity was significantly lower than the conventional value. PR results were investigated further, and isolated clusters were linked to damage modes anticipated at other specific regions of the stress history. A secondary series of experiments was performed on specimens representing the individual constituents of the CMC (single-phase SiC flexural bars, Hi-Nicalon™ fibre bundles and SiC f /SiC mini-composites) in attempts to further validate the corresponding AE signal characteristics. Matrix cracking and interphase debonding/sliding damage modes could be identified consistently, while fibre breaks remained difficult to isolate under the current experimental conditions.

Determining the interlaminar tensile strength of a SiCf/SiC ceramic matrix composite through diametrical compression testing

Interlaminar tensile strength (ILTS) of a SiC f /SiC Ceramic Matrix Composite (CMC) was determined through use of a diametrical compression test of disk geometries, with two geometries are investigated (Φ4.5 and Φ9 mm). Results are correlated with the fracture surface architecture, specifically relating to fibre tows. Due to the stochastic nature of ceramic material systems a Weibull distribution was implemented to understand the characteristic strength and distribution of the data sets for both disk geometries. Overall, a decrease in characteristic ILTS coupled with a narrowed distribution is observed for the Φ9 mm compared the Φ4.5 mm disk geometries due to the repeating unit cell size of the SiC f /SiC CMC under investigation.

Microstructure and strengthening behavior in high content SiC nanowires reinforced SiC composites

AbstractIn this study, the high‐content SiCnw reinforced SiC ceramic matrix composites (SiCnw/SiC CMC) were successfully fabricated by hot pressing β‐SiC and sintering additive (Al2O3‐Y2O3) with boron nitride interphase modification SiCnw. The effects of sintering additive content and mass fraction (5–25 wt%) of SiCnw on the density, microstructure, and mechanical properties of the composites were investigated. The results showed that with the increase of sintering additives from 10 wt% to 12 wt%, the relative density of the SiCnw/SiC CMC increased from 97.3% to 98.9%, attributed to the generated Y3Al5O12 (YAG) liquid phase from the Al2O3‐Y2O3 that promotes the rearrangement and migration of SiC grains. The comprehensive performance of the obtained composite with 15 wt% SiCnw possessed the optimal flexural strength and fracture toughness of 524 ± 30.24 MPa and 12.39 ± 0.49 MPa·m1/2, respectively. Besides, the fracture mode of the composites with 25 wt% SiCnw content revealed a pseudo‐plastic fracture behavior. It concludes that the 25 wt% SiCnw/SiC CMC was toughened by the fiber pull‐outs, debonding, bridging, and crack deflection that can consume plenty of fracture energy. The strategy of SiC nanowires worked as a main bearing phase for the fabrication of SiC/SiC CMC providing critical information for understanding the mechanical behavior of high toughness and high strength SiC nanoceramic matrix composites.

Influence of post heat treatment on the high-temperature performances of multi-layered thermal/environmental barrier coatings on SiC-based composites

Multi-layered LaMgAl11O19/Yb2Si2O7/Yb2Si2O7–Si/Si (LMA/YbDS/YbDS–Si/Si) thermal/environmental barrier coatings (T/EBCs) on SiC fibre-reinforced SiC ceramic matrix composites (SiCf/SiC–CMCs) were subjected to post heat treatment at 1200 or 1350 °C for 5 h. The thermal cycling and water-vapour/oxygen corrosion of the multi-layered T/EBCs after annealing at different temperatures were studied. The results showed the thermal cycling lifetime of the 1350 °C-annealed T/EBCs was shorter than those of the 1200 °C-annealed and as-sprayed T/EBCs, while the 1350 °C-annealed T/EBCs exhibited relatively outstanding resistance to steam corrosion. The degraded thermal cycling lifetime may be associated with horizontal cracks generated at the interfaces of the LMA and YbDS layers after annealing at 1350 °C, which weakened the bonds between the coating layers. The outstanding resistance to steam corrosion of the 1350 °C-annealed T/EBCs could be attributed to the formation of a Yb3Al5O12 reaction layer with low-oxygen permeability on the upward sides of the YbDS layers in the 1350 °C-annealed T/EBCs. This could reduce the oxidation of Si inclusions within the YbDS layers, leading to less silica volatilisation.

Xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4: A promising thermal/environmental barrier coating material for SiCf/SiC ceramic matrix composites

Rare-earth phosphates (REPO₄) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiC_f/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al₂O₃–SiO₂ (CMAS). Nevertheless, a relatively high thermal conductivity (<i>κ</i>) of the REPO₄ becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy_1/7Ho_1/7Er_1/7Tm_1/7Yb_1/7Lu_1/7Y_1/7)PO₄ (HE (7RE_1/7)PO₄) has been designed and synthesized for the first time to solve this issue. HE (7RE_1/7)PO₄ with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO₂ up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE_1/7)PO₄ (5.96×10⁻⁶ ℃⁻¹ from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE_1/7)PO₄ (from 4.38 W·m⁻¹·K⁻¹ at 100&nbsp;℃ to 2.25 W·m⁻¹·K⁻¹ at 1300 ℃) are significantly decreased compared to those of single-component REPO₄ with the minimum value ranging from 9.90 to 4.76 W·m⁻¹·K⁻¹. These results suggest that HE (7RE_1/7)PO₄ has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.

Preparation and properties of Ti3SiC2 preform reinforced SiC ceramic matrix composites

Ti3SiC2 preform reinforced SiC ceramic matrix composites (Ti3SiC2/SiC) were successfully fabricated through a novel near-net-shape process strategy combining molten salt synthesis with subsequent polymer infiltration and pyrolysis (PIP) for the first time. The effects of temperature and molten salt ratio on the phase composition, pore structure, and flexural strength of Ti3SiC2 preform were investigated in detail. The morphology and microstructure evolution of the composites during the PIP process were observed by SEM and TEM. The mechanical properties, electromagnetic interference shielding effectiveness (EMI SE) and thermal conductivity of Ti3SiC2/SiC were significantly improved compared to PDC-SiC, which benefits from the connected network skeleton of Ti3SiC2 preform. The flexural strength and fracture toughness of Ti3SiC2/SiC are 198.7 MPa and 4.5 MPa∙m1/2. The EMI SE remains above 30 dB covering the entire X-band and its average value is 46.92 dB. The thermal conductivity is 6–7 W/(m·k) (25–1000 °C).

Effect of Y2O3 Additive on Mechanical and Wear Behaviour of hBN Reinforced SiC Ceramic matrix composite

Effect of Y2O3 Additive on Mechanical and Wear Behaviour of hBN Reinforced SiC Ceramic matrix composite

Effects of hBN and Y2O3 Addition on Mechanical and Tribological Behavior of SiC Ceramic Matrix Composites Prepared by Spark Plasma Sintering

Effects of hBN and Y2O3 Addition on Mechanical and Tribological Behavior of SiC Ceramic Matrix Composites Prepared by Spark Plasma Sintering