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%.

Due to high tensile strength, excellent high-temperature and oxidation resistance, SiC fibers could be applied in many important fields such as aerospace and high-tech equipment. However, the current preparation temperature of domestically produced titanium-containing SiC fibers is relatively low, while the fibers are still full of excess oxygen and free carbon, which seriously affects their high-temperature resistance. In this work, the polytitanocarbosilane (PTCS) precursor was synthesized by using low-softening-point polycarbosilane (LPCS) and tetrabutyl titanate (Ti(OBu)₄). Mass fraction of titaniumin in the precursor was in the range of 0.36%-1.81%. The nearly stoichiometric polycrystalline SiC(Ti) fibers were successfully prepared through PTCS melt spinning, air curing, pyrolysis, and high-temperature sintering. Mass fractions of carbon and oxygen in SiC(Ti) fibers were 30.45% and <1.0%, respectively, with a C/Si ratio of approximately 1.05 and β-SiC grain size of 100-200 nm. The titanium element in SiC(Ti) fibers mainly existed in the form of TiC phase, which was beneficial to densification of the fibers during the sintering process. The SiC(Ti) fibers showed smooth and dense surface, exhibiting obvious transgranular fracture. Average tensile strength of the SiC(Ti) fibers was 2.04 GPa, and elastic modulus was 308 GPa. All results of this work provide important reference for the development of high-performance continuous SiC fibers.

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.

In response to the evolving landscape of high-speed aircraft, characterized by an expansive airspace, prolonged flight durations, and increased velocities, the thermal protection requirements for key structures such as the nose cone, leading edge, and engine combustion chamber have become more exacting. This necessitates a concerted focus on the development of high-performance thermal protection materials capable of withstanding extreme conditions. Ultra-high temperature ceramic composites have emerged as noteworthy candidates, showcasing exceptional oxidation and ablation resistance. Despite their commendable properties, the inherent brittleness of these composites poses a significant obstacle to widespread engineering applications. To address this limitation, there is a growing emphasis on toughening through structural modulation. Simultaneously, the imperative to enhance aircraft payload capacity underscores the demand for lightweight ultra-high temperature ceramic composites. This paper provides a systematic overview of the major research advances made in recent years on ultra-high temperature ceramic composites, including preparation methods such as pressure sintering, slurry infiltration, precursor impregnation and pyrolysis, reactive melt infiltration, chemical vapor infiltration/deposition, and “solid-liquid” combination process, toughening methods such as particles, whiskers, soft-phase materials, short-cut fibers, and continuous fibers, as well as oxidation ablation resistant properities and mechanisms, and lightweighting design. The relationship between the components, microstructures and properties of ultra-high temperature ceramic composites is discussed in depth, and the current challenges as well as the future development trends of ultra-high temperature ceramic composites are presented.

The development of high-speed flight technology has put forward an urgent demand for high- performance thermal structure materials. High-entropy carbides (HECs) ceramics are a fast-emerging family of materials that combine the excellent properties of high-entropy ceramics and ultra-high temperature ceramics. HECs have a broad application prospect in extreme service environments, which has received extensive attention from scholars in recent years. Compared with traditional ultra-high temperature carbides containing only one or two transition metal elements, HECs have a greater potential for development because of their improved comprehensive performance and greater designability of composition and properties. After successive exploration of HECs in recent years, researchers have obtained many interesting results, developed a variety of preparation methods, and gained comprehensive understanding of microstructure and properties. The basic theories and the laws on HECs obtained from experimental process are reviewed in this paper. Preparation methods of HECs including powders, blocks, coatings and films, as well as fiber-reinforced HECs-based composites are summarized. Research progress on the properties of HECs, such as the mechanical properties, thermal properties, and especially the oxidation and ablation resistance related to high-temperature applications, is reviewed and discussed. Finally, the scientific issues that need to be further explored in this area are emphasized, and the prospects are proposed.

Oxide ceramics, known for their outstanding strength and excellent oxidation and corrosion resistance, are prime candidates for high-temperature structural materials of aero-engines. These materials hold vast potential for application in high-end equipment fields of the aerospace industry. Compared with traditional ceramic preparation methods, laser additive manufacturing (LAM) can directly realize the integrated forming from raw powders to high-performance components in one step. LAM stands out for its high forming efficiency and good flexibility, enabling rapid production of large complex structural components with high performance and high precision. Recently, research on LAM for melt-grown oxide ceramics, which involves liquid-solid phase transition, has surged as a hot topic. This paper begins by outlining the basic principles of LAM technology, with an emphasis on the process characteristics of two typical LAM technologies: selective laser melting and laser directed energy deposition. On this basis, the paper summarizes the microstructure characteristics of several different oxide ceramics prepared by LAM and examines how process parameters influence these microstructures. The differences in mechanical properties of laser additive manufactured oxide ceramics with different systems are also summarized. Finally, the existing problems in this field are sorted out and analyzed, and the future development trend is prospected.

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.

Ti₃SiC₂ compound can enhance the oxidation resistance of C/C composites as a modifying material, thanks for its superior high-temperature stability, indicating significant potential for applications. In this work, titanium powder and liquid polycarbosilane (LPCS) were served as starting materials for producing Ti₃SiC₂ ceramics with four different phase contents by polymer derived ceramics (PDC) method at temperatures of 1200, 1300, 1400, and 1500 ℃, respectively. Effects of sintering temperature on the phase compositions and morphology of the ceramics were studied. Additionally, the impact of varying Ti₃SiC₂ phase contents on oxidation resistance and thermal shock resistance were also explored. The results showed that layered Ti₃SiC₂ formed at Ti : Si molar ratio of 3 : 1.5 when sintered at 1300, 1400, and 1500 ℃, respectively. After sintered at 1400 ℃, the mass fraction of Ti₃SiC₂ in the ceramic product reached 92.10% with the bending strength of 172.68 MPa. When subjected to a static air environment of 1300 ℃ for 7 h, the oxidation weight of the ceramics obtained progressively reduction with the increase of Ti₃SiC₂ phase content. During the oxidation process, a protective film primarily consisted of TiO₂ was formed on the surface, which effectively slowed down the oxygen diffusion into the interior. Air thermal shock tests at 1300 ℃ and flexural strength assessments demonstrated that the residual strength of all materials decreased with the increase of thermal shock times. Nevertheless, the thermal shock resistance and residual strength of the samples were enhanced with the increase of Ti₃SiC₂ phase content. After 30 times thermal shock, the sample with the mass fraction of Ti₃SiC₂ phase of 92.10% experienced 30.66% weight loss and retained residual strength of 120.18 MPa, primarily due to the layered structure of Ti₃SiC₂ which is significantly extends the crack propagation path and its superior oxidation resistance.

Hf_xTa_1-xC is a very promising candidate for thermal protection materials above 2000 ℃ due to its excellent properties such as high melting point, high hardness, high strength, high electrical conductivity, and high thermal conductivity. However, the rules of its mechanical properties and melting temperature varying with the composition remain elusive. Firstly, the mechanism of the variation of mechanical properties of Hf_xTa_1-xC system solid solutions with its components was systematically investigated from the microscopic point of view of covalent bond strength and valence electron concentration (VEC) based on the special quasirandom structures (SQS) method and first-principles calculations. It revealed that among the five components of solid solutions (i.e., HfC, Hf_0.75Ta_0.25C, Hf_0.5Ta_0.5C, Hf_0.25Ta_0.75C and TaC), the Hf_0.25Ta_0.75C solid solution possessed the largest elastic modulus and shear modulus. It was mainly attributed to two reasons: (1) the component possessing the strongest covalent bonding strength among the above ternary compounds; (2) the special bonding states between the p-orbital from C and the d-orbital from Hf or Ta strongly resisting the deformation and being completely filled near VEC=8.75 (for Hf_0.25Ta_0.75C). Secondly, the melting curves of the Hf_xTa_1-xC system solid solutions were calculated using the ab initio molecular dynamics (AIMD)-based molecular dynamics Z method. It showed that there existed indeed the phenomenon for anomalous increase in the melting temprature of Hf_xTa_1-xC system solid solutions, and the highest melting temperature of 4270 K was predicted on Hf_0.5Ta_0.5C, which was mainly attributed to the synergistic effect of the conformational entropy and the strength of the covalent bond. The results provide a theoretical guidance for the experimental selection of the optimal components of high melting temprature and high mechanical properties for Hf_xTa_1-xC system solid solutions in the thermal barrier coating applications, as well as a reference for the study of other transition metal carbides.

ZrB₂-based ceramics typically necessitate high temperature and pressure for sintering, whereas ZrB₂-SiC ceramics can be fabricated at 1500 ℃ using the process of reactive melt infiltration with Si. In comparison to the conventional preparation method, reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition. In this work, ZrSi₂, B₄C, and C were used as raw materials to prepare ZrB₂-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics. Control sample of ZrB₂-SiC was also prepared using ZrB₂ and SiC as raw materials through an identical process designated as ZS ceramics. Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB₂ phase in ZBC ceramics compared to the larger particles in ZS ceramics. Both sets of ceramics underwent cyclic oxidation testing in the air at 1600 ℃ for a cumulative duration of 5 cycles, each cycle lasting 2 h. Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO₂-ZrO₂ oxide layer on their surfaces during the oxidation. This layer severed as a barrier against oxygen. In ZBC ceramics, ZrO₂ is finely distributed in SiO₂, whereas in ZS ceramics, larger ZrO₂ particles coexist with glassy SiO₂. The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO₂ increases the viscosity of glassy SiO₂, preventing its crystallization during the cooling. Conversely, some SiO₂ in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO₂, leading to the formation of ZrSiO₄. This leads to cracking of the oxide layer due to differences in thermal expansion coefficients, weakening its barrier effect. An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics, suggesting superior oxidation resistance of ZBC ceramics.

The batch stability of ceramic powders is a core indicator that manufacturers of ceramic products are most concerned about, yet has long been undocumented. In this study, the similarity of Si₃N₄ powders produced in different batches was quantitatively evaluated by taking combustion-synthesized Si₃N₄ powders as the sample. A system of powder performance evaluation parameters covering static physicochemical and dynamic flowability indices was firstly constructed. Then, all performance data of Si₃N₄ powders in this parameter system were retested. Subsequently, the consistency evaluation data of Si₃N₄ powders were obtained using the cosine similarity method and the Euclidean distance method. The results show that both methods based on this parameter system can reflect the similarity between batches of powders and quantitatively show the differences between them. Calculation results of the two methods are mutually verified. For powders judged to be dissimilar, differences in the process were traced to find the key link in the consistency between the Si₃N₄ powders and the raw silicon powders. For powders judged to be highly similar, they were classified as the same class. These study provides a quantitative basis for the classification of different batches of silicon nitride powders. The “Powder Consistency Evaluation System” established in this work presents an effective evaluation tool and quantitative basis for batch stability (performance consistency) of silicon nitride powder.

SiC ceramics with high thickness and high density are highly advantageous for armor protection, but it is difficult to produce bulk SiC ceramics with thicknesses more than 100 mm. This work was concentrated on the problems of easy cracking and non-densification in the thick SiC ceramic sintering, and degreasing products as well as pressure-incomplete degreasing process were investigated. In order to degrease thick ceramics, phenolic resin’s pyrolysis residue was examined using TG-MS. Formaldehyde and other small-molecule byproducts of breakdown were quickly eliminated, but macromolecule byproducts like dimethylphenol were easily retained in the core, leading to the noncompact sintering of thick ceramics. After degreasing optimization, the blank’s surface-core density is almost constant, ranging from 1.81 to 1.84 g/cm³. In contrast, the test group shows no cracking or deformation after sintering at 2150 ℃, and both surface and core of the large thickness ceramics obtain a density up to 3.14 g/cm³ with similar microstructure. The fracture strength of the core is (411±84) MPa, while the fracture strength of the surface is (433±48) MPa. According to the investigation, the ceramic core’s insufficient degreasing is the primary reason for the cracking and poor density.

With the rise of the third-generation wide-bandgap semiconductors represented by SiC and GaN, power electronic devices are developing rapidly towards high output power and high power density, putting forward higher performance requirements on ceramic substrate materials used for power module packaging. The conventional Al₂O₃ and AlN ceramics are inadequate for the new generation of power module packaging applications due to low thermal conductivity or poor mechanical properties. In comparison, the newly developed Si₃N₄ ceramics have become the most potential insulating heat dissipation substrate materials due to its excellent mechanical properties and high thermal conductivity. In recent years, researchers have made a series of breakthroughs in the preparation of high strength and high thermal conductivity Si₃N₄ ceramics by screening effective sintering additive systems and optimizing the sintering processes. Meanwhile, as the advancement of the engineering application of coppered Si₃N₄ ceramic substrate, the evaluation of its mechanical, thermal, and electrical properties has become a research hotspot. Starting from the factors affecting thermal conductivity of Si₃N₄ ceramics, this article reviews the domestic and international research work focused on sintering aids selection and sintering processes improvement to enhance the thermal conductivity of Si₃N₄ ceramics. In addition, the latest progress in the dielectric breakdown strength of Si₃N₄ ceramic substrates and the evaluation of properties after being coppered are also systematically summarized and introduced. Based on above progresses and faced challengies, the future development direction of high strength and high thermal conductivity Si₃N₄ ceramic substrates is prospected.

As a high-temperature-resistant structural reinforcement material with excellent performance, alumina continuous fiber has been widely used in various fields. However, its large-scale preparation is still a great challenge due to the technical difficulty. Herein, the alumina continuous fibers were prepared using self-made aluminum sol and commercially available silica sol as precursors, in which the microstructure and composition of aluminum sol were studied to reveal their excellent spinnability. Preparation of alumina-based gel continuous fibers with length longer than 1500 m was realized by Sol-Gel combined dry spinning technology. After calcination at 1100 ℃ for 30 min, the continuous ceramic fiber composed of γ-Al₂O₃ and amorphous SiO₂ with the diameter and mean tensile strength of 10 μm and 2.0 GPa was successfully obtained. Microstructure analyses revealed high relative density of the ceramic fibers, in which the γ-Al₂O₃ nanocrystals with size of 10-20 nm uniformly distributed in amorphous SiO₂, resulting in excellent mechanical properties. This preparation process is environment-friendly, simple and controllable, showing great potential in practical application. The test for high temperature resistance revealed that the alumina continuous fiber can work for a long time at 1000 ℃ while it can endure as high as 1300 ℃ for a short-time service.

Polymer derived ceramic is one of the effective methods for producing ultra-high temperature ceramics and powders, but effect of source material type on precursor cross-linking degree and ceramic yield has rarely been reported. Here, TaC precursors were synthesized using two carbon sources and poly-tantalumoxane (PTO). Phase composition and microstructure of TaC ceramic powders from different carbon sources, tantalum/carbon mass ratios, and pyrolysis temperatures were characterized. It was found that PF-3 resin with C=C was effective in promoting the cross-linking of PTO and increasing the ceramic yield. When the mass ratio of PTO to PF-3 Resin was 1 : 0.25 and PTO to 2402 Resin was 1 : 0.4, TaC ceramic powders could be obtained at 1400 ℃ without residue Ta₂O₅. Ceramic yields of ceramic powders were 54.02% and 49.64%, and the crystal sizes were 47.2 and 60.9 nm, respectively. Therefore, PF-3 resin is able to reduce crystal size while increasing ceramic yield, but has less impact on the powder purity and particle size. The purity of TaC ceramic powders derived from different carbon sources are 96.50% and 97.36%, respectively, meanwhile the median diameters are 131 and 129 nm, respectively.

Porous silicon nitride (Si₃N₄) ceramics can be widely used in various fields, such as sound and shock absorption, filtration and so on, due to its high porosity and outstanding properties of ceramics. However, conventional preparation methods, such as gas-pressure/pressureless sintering, sintering reaction-bonded sintering and carbothermal reduction sintering, perform long sintering time, high energy consumption and high equipment requirements, which makes the preparation of porous Si₃N₄ ceramics expensive. Therefore, it is of great importance to explore a rapid and low-cost preparation method. In recent years, the direct preparation of porous Si₃N₄ ceramics by self-propagating high temperature synthesis (SHS) has showed great potential of which the heat released from the nitridation of Si powder could be used for the in-situ sintering of porous Si₃N₄ ceramics. In present paper, researches relating to the initiation of the SHS reaction, and microstructural evolution, mechanical properties, and reliability of the fabricated Si₃N₄ ceramics are summerized systematically. Porous Si₃N₄ ceramics with complete nitridation, excellent grain morphology and outstanding mechanical properties and reliability are obtained by adjusting raw materials and process parameters. Furthermore, the relationship between properties of grain boundary phase and high-temperature mechanical properties of SHS-fabricated porous Si₃N₄ ceramics is reviewed. Finally, the development direction of the self-propagating high temperature synthesis of porous Si₃N₄ ceramics is prospected.