Deepwater shaft sealing materials are one of the critical core technologies limiting the advancement of deepwater equipment. Silicon carbide (SiC) ceramics, due to their outstanding high modulus, high thermal conductivity, low density, and excellent corrosion resistance, have become an ideal choice for next-generation deep-sea sealing materials. The immense seawater pressure in deep-sea environments causes significant differences in corrosion and wear processes compared to conventional atmospheric pressure conditions. However, research on the corrosion and wear behavior of SiC ceramics in deep-sea environments remains relatively insufficient. In this study, the static pressure of artificial seawater was adjusted to simulate deep-sea conditions at depths ranging from 0 to 5 km. In-situ characterization of the materials’ performance in deep-sea environments was conducted, and the influence of static pressure on their corrosion and wear properties was explored. The results indicated that SiC ceramics exhibited outstanding corrosion resistance in deep-sea environments at depths between 0 and 5 km. After immersion for 200 h, no significant corrosion, oxidation, or seawater salt-related erosion was observed on the material’s surface, and no mass loss occurred. As seawater depth increased, the chemical reaction between SiC and water gradually weakened, further enhancing the corrosion resistance of SiC ceramics. After seawater corrosion, the mechanical properties of SiC ceramics remained stable. Flexural strength of the material decreased by less than 5% after 200 h-corrosion in a 5 km deep-sea environment, and Vickers hardness or fracture toughness changed little. Under seawater lubrication conditions, SiC ceramics exhibited excellent wear resistance, with a wear rate of 2×10^-8-4×10^-8 mm³/(N·m), much lower than that of the paired silicon nitride (Si₃N₄) ceramic material (4×10^-5-1×10^-4 mm³/(N·m)). Notably, as seawater depth increased, both the material’s resistance to water corrosion and the lubricating load-bearing capacity of seawater were significantly enhanced, leading to a decrease in wear rate with increasing depth. In conclusion, SiC ceramics demonstrate significant potential for application in deep-sea sealing technologies.

Aluminum nitride (AlN) ceramics exhibit exceptional thermal and electrical properties, making them highly promising candidates for electronic packaging applications and integrated circuits. Nevertheless, the hydrolysis of AlN powder results in formation of Al(OH)₃, which decomposes into Al₂O₃ during the subsequent sintering process. This reaction increases oxygen content, thereby degrading thermal conductivity of AlN ceramics and further imposing significant limitations on their processing and utilization. Consequently, surface modification of AlN powder is imperative to improve its hydrolysis resistance. In this work, a dual-agent modification strategy utilizing polyethylene glycol (PEG) and lauric acid (LA) was implemented through a straightforward wet ball-milling protocol, successfully forming a chemically bonded encapsulation layer on AlN particles. FT-IR and XPS analyses verified that carboxyl groups (-COOH) of LA engaged in esterification reactions with hydroxyl groups on the oxidized AlN surface, leading to formation of robust ester linkages. TEM images revealed a continuous encapsulation layer with a thickness ranging from 12.2 nm to 16.1 nm. Remarkably, the modified powder maintained a solution pH below 9 after 72 h immersion in water at 40 ℃, with no discernible alterations in phase composition and microscopic morphology. This chemically stable and low-solubility encapsulation layer effectively obstructs water diffusion pathways, thereby suppressing hydrolysis kinetics. Enhanced hydrolysis resistance was positively correlated with LA dosage. This work proposes an innovative encapsulation-based paradigm for developing hydrolysis-resistant AlN powders and advancing high-performance ceramic fabrication.

High-entropy carbide (HEC) ceramics are distinguished by their high hardness, oxidation resistance, corrosion resistance, wear resistance, and high thermal conductivity, positioning them as promising candidates for application in extreme environments. However, inherent brittleness of these high-entropy ceramics limits their further application. In order to enhance the toughness of HEC ceramics, polycarbosilane (PCS), a precursor of silicon carbide (SiC), was added into the precursor of (Zr, Hf, Nb, Ta, W)C high-entropy ceramic. The in-situ formed SiC (SiC_i) by pyrolysis of PCS can serve as reinforcement for HEC ceramics. The results demonstrate that the volume fraction of SiC in the ceramics obtained from the pyrolysis of PCS is 23.38%. The SiC phases, with an average grain size of 1.19 μm, are evenly distributed in the high-entropy ceramic matrix. The pyrolysis process of ceramic precursors was investigated, revealing that the pyrolysis products of PCS exit as amorphous O_x-Si-C_y at low pyrolysis temperature, while a crystalline SiC phase emerges when the pyrolysis temperature exceeds 1500 ℃. Bulk (Zr, Hf, Nb, Ta, W)C-SiC_i ceramic was prepared by hot-pressing of precursor-derived ceramic powders obtained through pyrolysis at 1600 ℃. Mechanical properties of (Zr, Hf, Nb, Ta, W)C-SiC_i ceramic bulk were investigated, and composite ceramic bulks toughened by commercial silicon carbide nanopowders or silicon carbide whiskers were also prepared for comparison. Compared with (Zr, Hf, Nb, Ta, W)C ceramic, all composite ceramic bulks exhibit enhanced flexural strength and toughness. Notably, the in-situ generated SiC_i via precursor-derived method shows the most significant toughening effect. Flexural strength and fracture toughness of (Zr, Hf, Nb, Ta, W)C-SiC_i ceramic are (698±9) MPa and (7.9±0.6) MPa·m^1/2, respectively, representing improvements of 17.71% and 41.07% compared to that of (Zr, Hf, Nb, Ta, W)C ceramic bulk. Taking all above data into comprehensive account, the improvement is mainly due to the small grain size and uniform distribution of SiC in the composite ceramics prepared via precursor-derived method, which enhance energy consumption and hinder crack propagation under external stress.

Compared with single-phase Y₂O₃ ceramics, Y₂O₃-MgO nanocomposite ceramics exhibit superior mechanical strength, hardness, thermal conductivity, and excellent infrared band transparency, endowing them a good infrared window material. However, harsh mechanical and thermal operating conditions impose stringent requirements on the optical and mechanical properties of infrared window materials. In this study, high-purity Y₂O₃-MgO nanocomposite powder was used as raw material, and Y₂O₃-MgO nanocomposite powders with different ZrO₂ contents, in which Zr⁴⁺ ions accounted for the percentage of Y³⁺ ions at 1%, 3% and 5%, were prepared by adding zirconium nitrate aqueous solution during ball milling. ZrO₂:Y₂O₃-MgO nanocomposite ceramics were fabricated by hot pressing sintering at 1350 ℃ and 35 MPa for 30 min. The influence of ZrO₂ content on the phase, microstructure, infrared transmittance, hardness, and bending strength of nanocomposite ceramics was systematically studied. The results showed that doping ZrO₂ dissolved and uniformly distributed in the Y₂O₃ lattice changed microstructure of Y₂O₃-MgO nanocomposite ceramics and caused lattice distortion, which had a significant impact on the optical and mechanical properties of Y₂O₃-MgO nanocomposite ceramics. The microstructures of ZrO₂:Y₂O₃-MgO nanocomposite ceramics reveal that increasing ZrO₂ content can hinder ceramic densification, resulting in obvious pores in 5%ZrO₂:Y₂O₃-MgO nanocomposite ceramic. Meanwhile, doping ZrO₂ can enhance the hardness and bending strength of Y₂O₃-MgO nanocomposite ceramics, which can be attributed to lattice distortion suppressing the dislocations’ motion. 3%ZrO₂:Y₂O₃-MgO nanocomposite ceramic has a dense microstructure, with a transmittance of ~82% in the range of 3-5 μm, while exhibiting a hardness of 11.43 GPa and a bending strength of 276.67 MPa.

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.

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.

Two-dimensional transition metal carbon/nitride MXenes show promising applications in various fields due to their remarkable electrical and mechanical properties. Recently, the research of high performance MXenes nanocomposites (including one-dimensional fibers, two-dimensional films and three-dimensional blocks) has made remarkable progress. However, the mechanical properties are still far lower than the intrinsic mechanical properties of MXenes nanosheets, mainly due to the key scientific problems of voids, misalignment of MXenes nanosheets and weak interfaces. In order to solve the above problems, the intrinsic mechanical properties of MXenes nanosheets are firstly discussed in this work, then the development of high performance MXenes nanocomposites are summarized, and the latest research progress of high performance MXenes nanocomposites is discussed in detail, including how to eliminate void, improve the orientation of MXene nanosheets and enhance the interface interaction. Meanwhile, the applications of high performance MXenes nanocomposites in the fields of electric heating, thermal camouflage, electromagnetic shielding, sensing and energy storage are introduced. Finally, the challenges and future development directions of high performance MXenes nanocomposites are proposed.

The development trend of high voltage, high current and high-power density of power semiconductor devices has raised the requirement for the heat dissipation capability and reliability of ceramic substrates in devices. Silicon nitride (Si₃N₄) ceramics, known for their high thermal conductivity and excellent mechanical properties, have emerged as a preferred thermal dissipation substrate material for high-power electronic devices. However, there is a significant gap between experimental and theoretical values of thermal conductivity in Si₃N₄ ceramics. The long period of heat preservation during preparation leads to excessive grain growth, compromising mechanical properties and increasing costs, which hinders large-scale application. Lattice oxygen defects act as main factor limiting thermal conductivity of Si₃N₄ ceramics. Now, researchers are exploring ways to promote removal of lattice oxygen and full development of bimodal morphology formation of Si₃N₄, by selecting non-oxide sintering additives to reduce the oxygen content in the system, adjusting the composition and properties of the liquid phase, constructing a “nitrogen-rich-oxygen-deficient” liquid phase, and regulating the dissolution and precipitation process in the liquid phase. These efforts aim to the synergistic optimization of thermal conductivity-mechanical properties of Si₃N₄ ceramics. Based on the elemental classification, we review the non-oxide sintering additives developed at domestic and abroad, explain how they improve the thermal conductivity of Si₃N₄ ceramics from liquid-phase modulation and microscopic morphology control, analyze the grain development and morphology evolution laws, and discusse the mechanism of lattice oxygen removal. The out look on future development of high thermal conductivity Si₃N₄ ceramics is also prospected.