Ultra-high temperature ceramic (UHTC) structural materials have emerged as critical candidates in the fields of aerospace, defense equipment, energy and power sectors due to their outstanding oxidation/ablation resistance, high-temperature strength retention, and thermal shock resistance in oxidative environments exceeding 1600 ℃. In recent years, extensive research has been achieved in both fundamental research and technological applications focusing on compositional control, structural design, fabrication techniques, and performance optimization of these materials. UHTC systems, characterized by carbides, borides and nitrides, are currently facing increasingly stringent demands for enhanced thermal performance in more complex environments. To further advance development of UHTC structural materials for such conditions, this paper systematically reviews the latest research progress in this field. Firstly, synthesis techniques of UHTC powders are elaborated. Subsequently, systems, densification methods and structural regulation strategies of UHTCs are presented. Furthermore, fabrication techniques and performance enhancement strategies of UHTC matrix composites (UHTCMCs), UHTCs modified carbon/carbon composites (UHTCs-C/C), and UHTC coatings are examined, with particular emphasis on the latest breakthroughs in oxidation/ablation resistance. Additionally, primary technical challenges related to the long-term stability and reliability of UHTC structural materials under extreme conditions are identified, and a forward-looking perspective on future development trends is provided.

In recent years, ZrB₂, as a representative material of ultra-high temperature ceramics (UHTCs), has become an important candidate material system for components of new generation aerospace vehicles. However, its practical application is limited by difficulties in material preparation and processing of complex components. This study aims to optimize sintering process of ZrB₂-based UHTCs by introducing HfSi₂ as a sintering aid, specifically addressing the challenge of densification caused by low intrinsic diffusion coefficient of traditional ZrB₂ ceramics. The research focuses on elucidating formation mechanism of core-rim structured borides and their role in enhancing densification of ZrB₂-HfSi₂ ceramics. Dense ZrB₂-HfSi₂ ceramics were successfully fabricated via hot-press sintering at 1600 ℃. The results reveal that softening of HfSi₂ phase during sintering effectively fills interparticle gaps, thereby facilitating low-temperature densification. Furthermore, during the holding stage, interdiffusion of Hf and Zr atoms through a dissolution-reprecipitation mechanism facilitates formation of a core-rim structured ZrB₂/(Zr,Hf)B₂ composite. This core-rim structure consists of ZrB₂ core encased by a (Zr,Hf)B₂ rim, characterized by a fully coherent interface (hexagonal P6/mmm symmetry) with a low lattice mismatch (<5%), ensuring interfacial stability. The ZrB₂-HfSi₂ ceramic exhibits a compressive strength of (1333±83) MPa, a Vickers hardness of (15.86±0.72) GPa, and a fracture toughness of (2.01±0.36) MPa·m^1/2. The ZrB₂-HfSi₂ ceramic demonstrates typical intergranular fracture behavior, with only a limited number of cleavage planes displaying core-rim structural features. These findings provide critical insights into low-temperature sintering of UHTCs and underscore potential of core-rim structures in advancing the preparation of high-performance ceramics.

Key components of aerospace power systems operating under extreme conditions, such as high loads, elevated temperatures, oxygen-rich environments, and wide-temperature-range alternating thermal shocks, impose stringent requirements on material mechanical properties, thermal stability, and oxidation resistance. Conventional thermally sprayed Al₂O₃ coatings, characterized by high hardness, excellent wear resistance, superior oxidation resistance, and good thermal stability, have been widely applied to aerospace, energy, and mechanical engineering fields. However, these coatings primarily consist of metastable γ-Al₂O₃ as the dominant crystalline phase, which exhibits inferior mechanical and thermal conductivity properties compared to α-Al₂O₃. This limitation hinders their effectiveness under extremely high-load conditions. To address this issue and enhance the overall coating performance, atmospheric plasma spraying (APS) was employed to fabricate Al₂O₃-GdAlO₃ (GAP) amorphous coating with a thickness of approximately 350 µm. The friction and wear behavior, along with the mechanical properties of the coating, were systematically investigated through a designed wear test under a load of 2000 N, a rotational speed of 500 r/min, and a duration of 1 h. Experimental results indicate that due to the high proportion of the amorphous phase and the optimized microstructure, the Al₂O₃-GAP coating exhibits excellent wear resistance and superior crack propagation resistance under high-speed and heavy-load friction conditions, significantly outperforming conventional polycrystalline Al₂O₃ coatings. Furthermore, the Al₂O₃-GAP coating demonstrates a lower and more stable friction coefficient, effectively reducing frictional surface temperature. This mitigates high-temperature oxidation and thermal damage while alleviating stress concentration effects. In summary, the Al₂O₃-GAP amorphous coating demonstrates remarkable advantages under high-load, high-speed friction conditions, providing a high-performance and reliable coating solution for the protection of critical aerospace power system components.

Joining of ceramic and metal meets the engineering needs for high-performance structural components. However, the significant difference in thermal expansion coefficients between metals and ceramics, as well as the poor wettability of metals on ceramic surfaces, makes the joining of ceramics and metals face many challenges. In this study, “flash joining” technology was used to achieve the rapid connection of metal Cu and 5YSZ (5% yttria stabilized zirconia, molar fraction) ceramics at a relatively low temperature under the assistance of electric field/current. The effects of electric field, current density, and joining time on the “flash joining” behavior and the degree of bonding between Cu and 5YSZ were investigated. Moreover, the mechanism of “flash joining” between Cu and 5YSZ was discussed. The results showed that the densest joint between Cu and 5YSZ was obtained at a temperature of 753 ℃, a current density of 10 A/cm² and a joining time of 3 min. However, the joint began to deteriorate and even fracture when the temperature, current and joining time were further increased. Electrochemical reactions occurred during the “flash joining” process, introducing oxygen vacancy defects. Phase and microstructural analyses indicated that atomic diffusion driven by electrochemical reactions facilitated the joining of Cu and 5YSZ, with Cu atoms diffusing into the 5YSZ lattice and reduced Zr atoms diffusing into the Cu lattice. In addition, the direction of the electric field had a significant impact on the bonding between Cu and 5YSZ. A good bond was achieved when the electric field was oriented from 5YSZ to Cu, while the bonding did not occur when the electric field direction was from Cu to 5YSZ.

CeO₂-ZrO₂ solid solution is generally synthesized through chemical precipitation, followed by high-temperature calcination. However, their grains under high-temperature calcination are prone to aggregate and grow, resulting in lower specific surface area, weaker adsorption and poorer catalytic performance. In this study, nanocrystalline CeO₂-ZrO₂ solid solutions were prepared by a simple one-step alcohothermal method, avoiding effects of high-temperature calcination on grain growth and specific surface area reduction. Crystal structure, morphologies and thermal stability of the synthesized CeO₂-ZrO₂ solid solutions were characterized, and arsenic removal performance was determined. The results show that the grains in nanocrystalline CeO₂-ZrO₂ solid solutions grow sufficiently with large specific surface areas, high particle purity and good dispersibility, leading to improved adsorption effect on As(III) in water. The arsenic adsorption results show that maximum adsorption capacity of Ce_0.8Zr_0.2O₂ sample can reach 160 mg/g at an As(III) equilibrium solubility of 95 mg/L, which is much higher than pure CeO₂ and ZrO₂ samples, as well as CeO₂-ZrO₂ solid solution prepared by traditional calcination method. In addition, the prepared Ce_0.8Zr_0.2O₂ solid solution maintains a high As(III) removal rate and good acid-alkali resistance within pH range of 3-9. The arsenic adsorption mechanisms indicate that As(III) ions in the solution form coordination bonds with metal ions on the surface of Ce_0.8Zr_0.2O₂ solid solution, which belongs to the chemical adsorption process.

In a high heat flux ablative environment, the surface temperature of aircraft rises rapidly, leading to traditional high thermal conductivity materials being ineffective at protecting internal metal components. In this study, continuous carbon fiber reinforced Li₂O-Al₂O₃-SiO₂ (C_f/LAS) glass ceramic composites doped with SiC particles (SiC_p) were prepared by slurry immersion winding and hot pressing sintering. Effect of matrix crystallinity on ablative properties of the composites under ultra-high heat flux was investigated. By utilizing heat absorption and low thermal conductivity characteristics associated with SiO₂ gasification within composite materials, both surface and internal temperatures of these materials are effectively reduced, thereby ensuring the safe operation of aircraft and electronic devices. Results indicate that the average linear ablation rate of composites doped with 10% (in mass) of SiC_p significantly decreases at a heat flux of 20 MW/m². Transmission electron microscope observation reveals that the doped glass matrix exhibits increased crystallinity, reduced internal stress, and minimized lattice distortion, thereby enhancing the composites’ high-temperature performance. However, excessive SiC_p doping leads to reduced crystallinity and deteriorated ablation performance. Ultimately, the average linear ablation rate of C_f/LAS composites with 10% (in mass) SiC_p at 20 MW/m² heat flux is comparable to that of commercial carbon/carbon composites, accompanied by providing lower thermal conductivity and higher bending strength. This novel high-performance C_f/LAS composite is cost-effective, short-cycled, and suitable for mass production, offering promising potential for widespread application in ablation-resistant components of hypersonic vehicles.

Continuous silicon carbide fiber reinforced silicon carbide (SiC_f/SiC) composites are widely utilized in the hot-end components of aero engines due to their exceptional properties and high-temperature resistance. To ensure the safety and reliability of SiC_f/SiC composite parts during service, it is crucial to investigate the evolution of their mechanical properties under prolonged high-temperature exposure. In this study, mini-SiC_f/SiC composites with a BN interface were fabricated using Cansas-II SiC fibers. These mini-SiC_f/SiC composites underwent heat treatment at 1100, 1200, and 1350 ℃ for durations of 5, 10, 50, 100, and 200 h, respectively, to examine the effects of high-temperature and long-term heat treatment on their mechanical properties and microstructure. The results show that at 1100 ℃, heat treatment has no significant impact on the mini-SiC_f/SiC composites. The mechanical properties remain largely unchanged, and the contribution fractions of each stage to the overall mechanical performance remain consistent. At 1200 ℃, short-term heat treatment shows minimal effects on the mini-SiC_f/SiC composites without notable change in tensile strength. However, prolonged heat treatment leads to damage in the SiC fibers, thereby decreasing their tensile strength. At 1350 ℃, heat treatment significantly improves the properties of the BN interface but causes severe damage to the SiC fibers, resulting in a marked decline in the mechanical properties of the mini composites. As the heat treatment duration increases, the extent of fiber damage intensifies, leading to a continuous deterioration in the mechanical performance of the composites.

Laminated Ta/Ta_0.5Hf_0.5C cermets, characterized by high strength, high toughness, and high-temperature resistance, are excellent candidate materials for structural applications in aerospace field. To further investigate ablation performance of Ta/Ta_0.5Hf_0.5C cermets under high-temperature environment, a high-frequency plasma wind tunnel was utilized to evaluate their ablation resistance at nearly 3000 ℃. Their phase composition and microstructure before and after ablation were characterized and analyzed. Results revealed that the laminated Ta/Ta_0.5Hf_0.5C cermets demonstrated remarkable ablation resistance, with a mass ablation rate of 0.061 g/s and a linear ablation rate of 0.019 mm/s. During the ablation process, distinctive ridge-groove surface morphologies and internal cracks were produced along the layered structure direction. These features were attributed to inconsistent ablation rates and thermal expansion coefficients of Ta metal layer and Ta_0.5Hf_0.5C ceramic layer. Specifically, the ridge region primarily consisted of Hf₆Ta₂O₁₇ formed by oxidation of Ta_0.5Hf_0.5C ceramic layer. This compound could stably exist at high temperatures to protect the interior of ceramic layer from further oxidation. In contrast, the groove region primarily comprised Ta₂O₅, which was formed by oxidation of Ta metal layer. Yet Ta₂O₅ had a tendency to melt and vaporize at elevated temperatures, potentially leading to ejection or loss toward the ablation edge. The cracks formed within the layered structure during cooling process after ablation were mainly generated by thermal stress acting on the Ta_0.5Hf_0.5C ceramic layer due to differences in thermal expansion coefficients between the layers. Additionally, the Ta₂C interfaces between metal and ceramic layers played a crucial role in branching, deflecting, and initiating micro-cracks, which endowed the material with good thermal shock resistance.

SiC/SiC composites have emerged as essential thermal structure materials for development of hypersonic vehicles and high thrust-to-weight ratio aero-engines. Design and utilization of boron-containing ceramic precursors as impregnation agents for precursor infiltration and pyrolysis (PIP) to introduce self-healing components into matrix represent a key strategy for enhancing the antioxidant properties of SiC/SiC composites. Here, borane pyridine or borane triethylamine were utilized as boron sources and subsequently mixed with a solid polycarbosilane (PCS) xylene solution to prepare different boron-modified PCS solutions. These solutions were used as PIP impregnation agents to fabricate various boron-modified SiC/PyC (pyrolytic carbon)/SiC composites. The physicochemical properties of boron-modified PCS-derived ceramics, along with the physical and mechanical properties of SiC/PyC/SiC composites before and after matrix boron modification, were investigated. Results demonstrated that addition of appropriate amounts of borane pyridine and borane triethylamine as boron sources in solid PCS solutions effectively introduced boron as a heterogeneous element into the derived SiC ceramics. Compared to PCS, the boron-modified PCS solutions (BP-1 and BP-2) exhibited increased ceramic yields. The derived ceramics exhibited a semi-crystalline β-SiC structure, with boron element contents of 1.7% and 2.2% (in mass), respectively. In contrast to unmodified composite, the boron-modified SiC/SiC composites exhibited negligible changes in density, apparent porosity, and fracture toughness. However, the flexural modulus increased from 116 GPa to 132 GPa. Furthermore, the flexural strength of the modified composite using borane pyridine alone as boron source was 658 MPa, comparable to the unmodified composite's strength of 643 MPa, but with a reduced dispersion coefficient. All above data demonstrate that borane pyridine can be used as boron source for preparation of boron-modified SiC/SiC composites, providing valuable insights for developing high-performance SiC/SiC composite hot-end components.

Fine-diameter continuous SiC fibers are considered one of the most effective reinforcing fibers for advanced ceramic matrix composites, possessing significant application potential in aerospace and nuclear industries. Among them, near-stoichiometric SiC fibers characterized by a highly crystalline microstructure have garnered considerable attention due to their exceptional high-temperature resistance. However, influence of high-temperature sintering conditions on composition and microstructure of the fibers is still unclear. Here, influences of different sintering temperatures and durations on decomposition of the SiC_xO_y phase, grain growth and densification of the fibers were systematically investigated. It was found that decomposition of SiC_xO_y and densification of fibers occur progressively from surface to core. Notably, a specific sintering temperature of 1800 ℃ was identified as optimal, wherein growth of β-SiC grains effectively compensated for the pore defects resulting from the decomposition of SiC_xO_y phase, thereby achieving fiber densification. Conversely, excessively high sintering temperature might result in decomposition of β-SiC grains. Although extending sintering duration facilitated removal of residual oxygen within the fibers, it could cause accumulation of graphite phases at β-SiC grain boundaries, leading to an increase in pore defects within the fiber core. Finally, near-stoichiometric SiC fibers with highly crystalline microstructure were successfully fabricated through optimization of sintering conditions, possessing a composition of SiC_1.04O_0.02Al_<0.01. The β-SiC grains within the fibers were uniformly distributed with sizes ranging from 100 to 200 nm. The fibers exhibited a tensile strength of 1.88 GPa and a Young’s modulus of 373 GPa, accompanied by a high density of 3.1 g/cm³. The findings of this research provide a robust foundation for further improving comprehensive properties of SiC fibers.

Continuous carbon fiber reinforced silicon carbide (C/SiC) composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection. However, research on in-plane impact damage and multiple impact damage of C/SiC composites is limited. To investigate the in-plane impact damage behavior of C/SiC composites, a drop-weight impact test method was developed for strip samples, and these results were subsequently compared with those of C/SiC composite plates. Results show that the in-plane impact behavior of C/SiC strip samples is similar to that of C/SiC composite plates. Variation of the impact load with displacement is characterized by three stages: a nearly linear stage, a severe load drop stage, and a rebound stage where displacement occurs after the impact energy exceeds its peak value. Impact damage behavior under single and multiple impacts on 2D plain and 3D needled C/SiC composites was investigated at different impact energies and durations. Crack propagation in C/SiC composites was studied by computerized tomography (CT) technique. In the 2D plain C/SiC composite, load propagation between layers is hindered during impact, leading to delamination and 90° fiber brittle fracture. The crack length perpendicular to the impact direction increases with impact energy increases, resulting in more serious 0° fiber fracture and a larger area of fiber loss. In the 3D needled C/SiC composite, load propagates between the layers during impact through the connection of needled fibers. The fibers continue to provide substantial structural support, with notable instances of fiber pull-off and debonding. Consequently, the impact resistance is superior to that of 2D plain C/SiC composite. When the 3D needled C/SiC composite undergoes two successive impacts of 1.5 J, the energy absorption efficiency of the second impact is significantly lower, accompanied by a smaller impact displacement. Moreover, the total energy absorption efficiency of these two impacts of 1.5 J is lower than that of a single 3.0 J impact.

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.