Degradation of SiC_f/SiC composites in-plane shear performance after thermal shock represents a significant challenge for the development of hot-end components in aero-engines. In this study, thermal shock performance of 2D SiC_f/SiC was evaluated by using precision temperature-controlled thermal shock equipment, and correlation between thermal shock and in-plane shear performance was established. The results showed that borosilicate glass (BSG) coating caused SiC matrix forming BSG bubbles and oxidation, while BN interfacial debonding worsened with increasing number of thermal shocks. However, the thermal shock did not affect matrix cracking and fiber bridging. Furthermore, the in-plane shear stress-strain curve maintained bilinear trend. The degradation of the in-plane shear mechanism was attributed to the thermal expansion mismatch and the oxidation of SiC matrix. The in-plane shear modulus decreased from 78.5 to 63.6 GPa, the in-plane proportional limit stress decreased from 128.9 to 99.3 MPa, and the in-plane shear stress decreased from 205.8 to 187.3 MPa. According to the in-plane shear mixing rules, the degradation of shear modulus was caused by increased interface debonding. Combined with matrix cracking stress equation, this indicated that volume fraction decreased due to SiC matrix oxidation, resulting in degradation of proportional limit stress. Based on modified rigid body sliding model, using fiber step spacing could predict the degradation of in-plane shear strength after thermal shock, with the error between the theoretical calculation results and the actual values less than 20%.

Preparation of carbon-carbon composites through the chemical vapor infiltration (CVI) process, utilizing CH₄ and C₂H₅OH as precursors, can effectively improve the deposition rate and produce highly structured pyrolytic carbon. Understanding the reaction mechanism is essential for computational fluid dynamics (CFD) studies. Chemical reaction mechanisms typically involve numerous free radicals and reactions, and manually constructing such mechanisms based on experimental data alone risks omitting critical species and reactions. Hence, in this research, a thorough gas-phase pyrolysis kinetic mechanism for the CH₄+C₂H₅OH+Ar system was developed using the reaction mechanism generator (RMG). This mechanism included 31 core species and 214 core reactions, accurately predicting the evolution of major species' formation and consumption. The simulation results were consistent with experimental observations. Through a detailed analysis of the kinetics and sensitivity of reactants and critical products, reactions influencing the formation and consumption of crucial species were identified. Reaction pathway analysis further clarified relationships among different species, identifying core species within the mechanism. By simplifying the detailed mechanism based on sensitivity and rection pathway analysis at 1373 K and 10 kPa, a gas-phase kinetic mechanism was derived, composed of 18 species and 44 reactions. This streamlined model substantially boosts computational efficiency while retaining key species, providing a more convenient foundation for further CFD studies and applications.

Hexagonal boron nitride (h-BN) ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles, owing to their superior thermal stability and excellent dielectric properties. However, their densification during sintering still poses challenges for researchers, and their mechanical properties are rather unsatisfactory. In this study, SrAl₂Si₂O₈ (SAS), with low melting point and high strength, was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness. Then, BN-SAS ceramic composites were fabricated via hot press sintering using h-BN, SrCO₃, Al₂O₃, and SiO₂ as raw materials, and effects of sintering pressure on their microstructure, mechanical property, and thermal property were investigated. The thermal shock resistance of BN-SAS ceramic composites was evaluated. Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl₂Si₂O₈. With the increase of sintering pressure, the composites’ densities increase, and the mechanical properties shew a rising trend followed by a slight decline. At a sintering pressure of 20 MPa, their bending strength and fracture toughness are (138±4) MPa and (1.84±0.05) MPa·m^1/2, respectively. Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion, with an average of 2.96×10^-6 K^-1 in the temperature range from 200 to 1200 ℃. The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^-1·K^-1 within the temperature range from room temperature to 1000 ℃. Notably, BN-SAS composites exhibit remarkable thermal shock resistance, with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400 ℃. The maximum residual bending strength is recorded at a temperature difference of 800 ℃, with a residual strength retention rate of 101%. As the thermal shock temperature difference increase, the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.

Owing to the high strength/toughness and excellent anti-oxidation ability, continuous fiber reinforced ceramic matrix composites have become the preferred candidates for high temperature structural materials in aerospace field. Reactive melt infiltration can achieve the large-scale, short-cycle and low-cost production of ceramic matrix composites, which has been widely considered to be one of the most promising technologies from a commercial perspective. However, the mechanical and anti-oxidation/ablation properties of obtained composites prepared by conventional reactive melt infiltration are not satisfactory due to the existence of residual carbon and corroded fibers. In order to address the problems, relevant researchers constructed porous carbon matrix to replace conventional densified structure to promote its ceramic transformation and the consumption of reactive melt, thus achieving the improved performance of ceramic matrix composites. This paper reviewed the research progress about the preparation of SiC ceramics, SiC/SiC composites, C/SiC composites, and ultra-high temperature ceramic matrix composites by porous carbon ceramization strategy. Besides, the superiority of the method was verified compared to conventional reactive melt infiltration. The development of preparation methods for porous carbon matrix was also summarized. Finally, in term of the requirements of basic theory and technology for advanced ceramic matrix composites, the prospect for the future development of improved reactive melt infiltration to prepared ceramic matrix composites was discussed.

Continuous SiC fiber-reinforced SiC (SiC_f/SiC) composites possess high specific strength, high specific modulus, high-temperature resistance, and radiation resistance, making them suitable for applications in hot-end parts of advanced aero-engines and claddings of nuclear reactors. SiC_f/SiC composites are composed of fibers, interfaces and matrix, endowing them with complex multi-scale structural characteristics. These composites are designed to serve in harsh environment, and their damage and failure process are complex. A profound understanding and accurate analysis of damage and failure mechanisms of SiC_f/SiC composites under service environments are of great significance for the optimized design of materials and the reliable service of components. Traditional “post-mortem analysis” methods are incapable of acquiring data during the damage and failure process of materials under complex service environments. Therefore, there is an urgent need to develop in-situ characterization techniques for composites under high-temperature service environments. This paper reviewed the principles, advantages, and limitations of in-situ monitoring methods based on scanning electron microscopy, digital image correlation, micro computational tomography, acoustic emission, and electrical resistance. It focused on the latest research progress in the high-temperature mechanical characterization of SiC_f/SiC composites using various in-situ monitoring methods and combinations thereof. It summarized the challenges in the in-situ monitoring technologies of SiC_f/SiC composites under high-temperature environments and provided a preliminary outlook on the future development directions, such as the combined use of multiple in-situ monitoring techniques, new detection technologies like terahertz radiation, and in-situ damage monitoring methods for complex components.

High-entropy boride ceramics (HEBs) consisting of four or more principle metallic elements rapidly develop in recent years due to their outstanding unique physical properties and excellent elevated temperature properties, showing extraordinary promise as potential thermal protection materials applied in extreme environments. However, on the basis of unclear role of each element on their oxidation reaction, HEBs are generally difficult to densify because of their low self-diffusion coefficients and possible sluggish diffusion effect, resulting in limited mechanical properties and low oxidation resistance. In this work, a novel type of HEBs, (Ti_0.25Zr_0.25Hf_0.25Ta_0.25)B₂-B₄C composites, were prepared by boro/carbothermal reduction method combined with hot-pressing sintering at 1900 ℃. The effect of B₄C at the volume fractions ranging from 10% to 30% on the mechanical properties and oxidation resistance of the composites was systematically investigated. Microstructure analyses indicate that homogenously distributed B₄C can suppress grain growth of the HEBs matrix and promote toughening mechanisms such as crack deflection and crack branching, consequently resulting in strengthening and toughening composites. When the volume fraction of B₄C is 20%, the as-prepared composite shows a high relative density (96.1%) and good mechanical properties with Vickers hardness of (24.6±1.1) GPa, flexural strength of (570.0±27.6) MPa and fracture toughness of (5.58±0.36) MPa·m^1/2. In addition, exploration on the oxidation resistance of (Ti_0.25Zr_0.25Hf_0.25Ta_0.25)B₂-B₄C composites at temperatures ranging from 800 ℃ to 1400 ℃ shows that excellent oxidation resistance occurs at the chosen temperatures due to the formation of a dense and continuous oxidation scale, which acts as a barrier layer preventing oxygen inward diffusion. The main compositions of the oxide scale are TiO_x, (Zr, Hf)O₂ oxides and B₂O₃ at 800 ℃, while multicomponent oxidation products of (Zr, Hf, Ta)O_x, (Zr, Hf)O₂ and TiTaO₄ are formed in the oxide scale at 1100 ℃. As the temperature increased to 1400 ℃, thickness of the oxide layer significantly increases due to their volatilization of B₂O₃, while continuous B₂O₃ glassy phase plays a crucial role in the oxidation process of HEBs. When the B₄C volume fraction not less than 20%, TiTa₂O₇ and TiO₂ which were embedded in B₂O₃ glass, could effectively insulate inward oxygen and interfacial oxide thickness and enhance oxidation resistance of the composites. In summary, the primary work can be used as a reference to the researches relating to optimizing mechanical properties and oxidation resistance for HEBs.

In response to the urgent demand for ultra-high temperature ceramic matrix composites with integrated thermal protection and load-bearing capabilities for high-speed aircrafts, this study prepared stable ceramic slurry from submicron HfC ceramic powder, and utilized the slurry pressure impregnation-assisted precursor infiltration pyrolysis (PIP) process to fabricate C/HfC-SiC composites with uniformly distributed HfC matrix to overcome the shortcomings of the existing reaction-derived HfC precursor, such as high cost, low efficiency, and poor densification effect. The influence of HfC content on the microstructure, mechanical properties, and ablation resistance of composites was investigated. Results showed that the composites had density of 2.20-2.58 g·cm^-3 and open porosity of approximately 5% when the actual volume fraction of HfC was in range of 13.1%-20.3%. Utilizing a single layer of carbon cloth to impregnate the ceramic slurry with pressure, HfC particles were able to disperse into the interior of the fiber bundle and distributed relatively evenly in the composites. Increasing the HfC content resulted in reducted fiber content, and decreased mechanical properties of composites. Specifically, when HfC volume fraction was 20.3%, the composites exhibited density, tensile strength and fracture toughness of 2.58 g·cm^-3, 147 MPa and 9.3 MPa·m^1/2, respectively. Following 60 s of ablation under an oxygen acetylene flame, the composites demonstrated linear ablation rate of 0.0062 mm/s and mass ablation rate of 0.005 g/s. The molten phase Hf_xSi_yO_z formed during the ablation process could effectively cover the composites surface and provide protection.

High-performance structural material components are widely researched because of their curcial applications in aerospace, transportation and automotive, electronic information, metallurgy, and other fields. Traditional methods for enhancing the overall performance of structural material components mainly include improving intrinsic material properties and optimizing structural composite design. However, research on enhancing the intrinsic mechanical properties of single structural materials is reaching its limits. This study aims to explore a new paradigm for the development of high-performance structural composites by proposing the concept of periodic ordered structural materials and preparing the structural composites with improved overall properties through integrated sintering. The TiB-Ti functional unit with high hardness of ceramics and strong toughness of metal was structured through periodical sequencing, and high-performance TiB-Ti structural composites with different periodical sequencing modes were designed and prepared. On this basis, the mechanical properties of these structures were investigated, and their fracture modes were analyzed to understand how different ordering modes affect the overall properties of the materials. The results show that periodic ordered structure can improve the overall performance of materials by altering their macroscopic fracture modes and stress distribution properties. This new paradigm of research provides valuable insights and guidance for the structural design and performance breakthrough of other structural composites. Future research may focus on the exploration of the complexity of the periodic ordered structure modes, identifying potential application scenarios for these materials, and conducting additional performance testing studies.

Continuous fiber-reinforced ceramic matrix composites are widely used for high temperature components like aerospace engines due to their superior performance at elevated temperature. However, these materials are susceptible to damage from foreign object debris during service, which has become a significant concern. To investigate the impact damage characteristics of 2D-SiC/SiC composites, this study utilized a light gas gun to subject specimens prepared using chemical vapor infiltration (CVI) technology to ballistic impact. The impact processes were recorded with a high-speed camera, while the surface and internal structures of foreign object damage (FOD) were examined by optical microscopy and computed tomography (CT). This investigation revealed that conical cracks, interlaminar delamination, fiber fracture, and matrix collapse were the primary manifestations of high-speed impact damage. Damage characterization indicated that backside damage and edge delamination damage were caused by reflected tensile waves. As the impact velocity increased, the combined action of the projectile and tensile waves resulted in specimen penetration and weakening of edge delamination damage. Quasi-static tensile tests on high-speed impact specimens elucidated the relationship between residual mechanical properties and impact velocity, as well as projectile diameter. The results showed that residual tensile strength was a crucial parameter indicative of the severity of impact damage. Additionally, digital image correlation (DIC) was employed to determine strain distribution during tensile processes. By integrating residual tensile strength after impact with different projectile diameters and impact velocities, the study further explored the effect of varied parameters on impact damage. The research findings highlighted that projectile diameter as the primary factor influencing the extent of high-speed impact damage.

MAX phase ceramics, with their mixed covalent-metallic-ionic atomic bonds, can uniquely combine the advantages of both metals and ceramics, offering a series of distinctive characteristics. The particular layered atomic structure further endows them with decent fracture toughness, good damping capacity, and self-lubricating property. As such, MAX phase ceramics are more appealing to serve as reinforcements for metal matrix composites (MMCs) than conventional ceramic materials. Here, we foused on the development. To date, fabrication of MMCs reinforced by MAX phase ceramics still involves the use of stir casting, powder metallurgy, and melt infiltration techniques. The obtained composites made by different methods may display distinct differences in their structural characteristics, show notable enhancement in strength, hardness, and stiffness as compared to their metal matrices, and exhibit good wear resistance, high electrical conductivity and remarkable arc erosion resistance. Moreover, ultrafine MAX phase platelets can be preferentially oriented and aligned, e.g., by using vacuum filtration or ice templating techniques. By infiltrating metal melt into partially sintered porous ceramic scaffolds, bioinspired composites with nacre-like architectures can be obtained, thereby affording further improvement in strength and fracture toughness. Sufficient combinations of mechanical and functional properties enable the MMCs reinforced by MAX phase ceramics promising for a variety of applications, such as load-bearing structures, electrical contact materials. These composites can offer enhanced strength, stiffness, and wear resistance, making them ideal candidates for these applications.

Silicon carbide ceramics are important engineering materials, but their application is limited by the inherent brittleness. Two-dimensional graphene, with its excellent properties, can be used as a second phase to improve the performance of silicon carbide ceramics. However, due to poor dispersion of graphene in the ceramic matrix, it is a challenge to fully exploit the modifying effect of graphene in composite materials. To address these challenges, SiC-based ceramic materials incorporating graphene nanosheets (GNPs) were synthesized using ceramic organic precursor polycarbosilane and industrial expandable graphite as starting materials. The precursor intercalation technique was employed to fabricate SiC/GNPs ceramic composites with GNPs volume fraction of 1%, 3%, and 5%. The GNPs were uniformly arranged in an array-like parallel fashion in the SiC ceramic matrix, showing excellent orientation. With the GNPs content increasing, the spacing between GNPs within the array decreased, indicating tunable microstructural topology. The addition of GNPs greatly enhanced the fracture toughness of SiC ceramics. When the GNPs content was 3%, the relative density of the samples reached 98.5%, the bending strength reached 445 MPa, and the fracture toughness (K_IC value) peaked at 5.67 MPa·m^1/2, surpassing pure SiC ceramics by 40%, which was primarily attributed to crack deflection and bridging induced by the GNPs. However, further increase in GNPs content led to a decrease in fracture toughness to 4.37 MPa·m^1/2. These SiC-based ceramic composites with a graphene array have potential application in design and development of novel “structure-function integration” SiC-based ceramic devices.

Low-velocity impact is an inevitable problem in the service of ceramic matrix composites structures in high speed aircraft. Therefore, the damage type and residual bearing capacity after low-velocity impact are critical factors for ensuring the safety of the aircraft structures. In this study, two-dimensional braided SiC/SiC composite laminates were taken as the research objects, and low-speed impact tests under different energies were carried out. The damage morphology of SiC/SiC composites was observed by computed tomography, and the damage mechanism of SiC/SiC composites during the impact process was revealed by analyzing the load history curve and strain history curve. Post-impact residual strength tests were carried out on specimens with barely visible damage and the effect of barely visible damage on the residual strength of SiC/SiC composites was investigated. The results showed that under low-velocity impact load, surface damage of specimens mainly included no surface damage, barely visible damage, semi-penetrating damage and penetrating damage. Internal damage of specimens mainly included cone cracks, yarn breakage and delamination. The residual properties of SiC/SiC composites were found to be severely affected by low velocity impact damage. The residual compressive strength of the specimen with barely visible damage was 81% of that of the undamaged specimens, and the residual tensile strength was only 68% of that of the undamaged specimens.

AlN-SiC multiphase ceramics possess robust mechanical strength, high thermal conductivity and good oxidization resistance, and show great potential as the matrix material of fiber reinforced ceramic matrix composites. In this work, AlN-SiC multiphase ceramics were fabricated via low temperature reactive melt infiltration of Si-Al alloy into porous C-Si₃N₄ preforms. Influence of Si-Al source on the melt infiltration process was studied, and impact of residual silicon on the mechanical and thermal properties of the AlN-SiC ceramics was investigated. It was found that an Al-O layer was in-situ formed at the interface between Si-Al melt and C-Si₃N₄ preform, when Si-Al powder was used as the infiltration medium. This seriously retarded the melt infiltration process and made the penetration of Si-Al melt into the C-Si₃N₄ preform hardly possible. However, when Si-Al ingot was used as the infiltration medium, a well infiltration of Si-Al melt into the C-Si₃N₄ preform occurred, which led to the formation of dense AlN-SiC ceramics. Mechanical and thermal property measurements indicated that the strength of the AlN-SiC ceramics was significantly improved as the residual silicon content in it was reduced, while a reverse trend was observed for the thermal conductivity. AlN-SiC ceramics with 4%(in mass) residual silicon showed a high strength of 320.1 MPa, nearly comparable to that of conventional reaction bonded SiC, although its thermal conductivity was modest (26.3 W·m^-1·K^-1). The fundamental reasons for the above phenomena were discussed. This study is of great significance for the preparation of SiC_f/AlN-SiC composites by low temperature reactive melt infiltration.

To study the mechanical properties at high temperature of pre-stressed ceramics which were prepared by using higher expansion coefficient materials as coating and lower expansion coefficient materials as substrate, zirconia and alumina were chosen as the coating and the substrate, respectively, to fabricate ZrO₂-Al₂O₃ (marked as ZcAs) pre-stressed ceramics with sandwich structure. Meanwhile, Al₂O₃-ZrO₂ pre-stressed ceramics (marked as AcZs, which has the similar section ratio between substrate and coating to ZcAs), ZrO₂ ceramics and Al₂O₃ ceramics were set as the reference samples. Combining the results of bending strength at different temperatures with the results of Vickers indentation, the existence form of residual stress and its influence on crack propagation behavior were clarified as well as the temperature dependence of residual stress. Results show that the residual tensile stress exists in the surface layer of ZcAs, while the compressive stress exists in the substrate. On the contrary, the compressive stress exists in the surface layer of AcZs and tensile stress exists in the substrate. Due to tensile stress promoting while compressive stress inhibiting crack growth, flexural strength of ZcAs is 13.2% lower than that of Al₂O₃, and AcZs possesses strength 25.0% higher than that of ZrO₂ at room temperature. In addition, both tensile stress and compressive stress are decreased with the increase of temperature, which is mainly attributed to the relaxation of pre-stress caused by high temperature.

Controlling the structure and properties of low-density C/C porous preforms is the key to the preparation of C/C-SiC composites with excellent friction and wear properties. In this study, C/C porous preforms prepared by chemical vapor infiltration were subjected to high temperature heat-treatment at 2100 ℃. C/C-SiC composites were prepared by reactive melt infiltration. Effects of high temperature heat-treatment of C/C porous preforms on microstructures, thermal properties and tribological properties of C/C-SiC composites were investigated. The results showed that the porosity and graphitization degree of the C/C porous performs increased after high temperature heat-treatment at 2100 ℃. The C/C-SiC composites have a higher density (2.22 g/cm³), and the porosity is reduced from 5.1% to 3.4%, the phase content of SiC ceramic is increased by 11.9%. The mean free path of phonons is larger when C/C porous preforms have a higher degree of graphitization, resulting in thermal conductivity at room temperature being increased by 2.1 times, and the thermal conductivity at 1200 ℃ being increased by 0.2 times. Wear surface of C/C-SiC composites forms a continuous and stable friction film, which is attributed to the fact that the PyC after high temperature treatment is softer and easier to be extruded into a film. Thus, the friction coefficient is more stable, and the wear rate is reduced under the test loads of 3, 6 and 9 N, by 47.8%, 41.9% and 11.7%, and the average friction coefficients are 0.47, 0.38 and 0.39, respectively. Therefore, high temperature heat-treatment of the C/C porous preforms can improve the thermal conductivity of the C/C-SiC composites, which exhibits a more stable friction coefficient and more wear-resistant.

Continuous silicon carbide fiber reinforced silicon carbide composite (SiC_f/SiC) is a key material for the advanced aero-engines. It is required to possess excellent high-temperature creep resistance for SiC_f/SiC to meet the long-term service lifetime of the aero-engines. Here, tensile creep behaviors of a plain woven Cansas-II SiC_f/SiC (2D-SiC_f/SiC) were investiged in the temperature of 1200-1400 ℃ with the stress levels of 80 to 140 MPa. Its microstructure and fracture morphology were observed, and composition was analyzed. Results show that creep-rupture time of 2D-SiC_f/SiC is more than 500 h and steady-state creep rate is 1×10^-10-5×10^-10 /s at stresses lower than the proportional limit stress (σ_PLS). The creep behaviors are controlled by matrix and fibers. The creep-rupture time is significantly reduced, and the steady-state creep rate is increased by an order of magnitude when the stress is higher than the σ_PLS. The matrix, fibers and interfaces of the composite are greatly oxidized, and the creep behaviors are mainly controlled by the fibers.

Silicon carbide ceramic matrix composites have been widely used in aerospace, friction brake, fusion fields and so on, and become advanced high-temperature structural and functional composites, due to their high specific strength and specific modulus, excellent ablation and oxidation resistance, and high conductivity and good thermal shock resistance. This paper reviews the latest research progress in preparation and property of silicon carbide ceramics matrix composites (CMCs) with high thermal conductivity. Researchers have improved the thermal conductivity of silicon carbide CMCs, including by introducing highly thermal conductive phases for reinforcing heat transport, such as diamond powders, and mesophase pitch-based carbon fibers (MPCF), by optimizing the interface between pyrolytic carbon (PyC) and silicon carbide matrix for reducing interfacial thermal resistance, by heat-treating for obtaining silicon carbide matrix with higher crystallinity and better thermal conductivity, and by designing preform structure for establishing continuous thermal conduction path. Meanwhile, research interests on silicon carbide CMCs are to explore new preparation with high efficiency and low cost through optimising their influencing factors, and to obtain isotropic highly thermal conductivity with dimensional stability and physical properties through deep understanding their thermal conductive mechanism, and flexible method based on the structure-activity relationship.