Si₃N₄ fiber-reinforced ceramic composites are promising candidates for high-temperature wave-transparent applications, yet the relationships among composition, interfacial characteristics, and mechanical performance remain inadequately understood. This study designs three kinds of composites, Si₃N_4f/BN, Si₃N_4f/SiO₂, and Si₃N_4f/SiO₂–BN, and systematically investigates their performances. The results reveal that the reaction between the BN precursors and silanol groups in the SiO₂ matrix during the fabrication of Si₃N_4f/SiO₂–BN enhances the chemical compatibility between the fiber and matrix, promoting elemental interdiffusion and forming a thicker interfacial diffusion region. Consequently, the interfacial shear strength of Si₃N_4f/SiO₂–BN is 1.86 and 2.35 times that of Si₃N_4f/BN and Si₃N_4f/SiO₂, respectively. The stronger fiber-matrix bonding in Si₃N_4f/SiO₂–BN suppresses fiber pull-out, whereas the weaker bonding in the other two composites permits it. Si₃N_4f/BN primarily exhibits fiber bundle pull-out, whereas Si₃N_4f/SiO₂ shows long single-fiber pull-out, indicating improved damage tolerance. In contrast, Si₃N_4f/SiO₂–BN displays a typical brittle fracture behavior with minimal fiber pull-out and degraded mechanical properties. The excessive interfacial bonding, together with the thermal residual stress arising from the thermal expansion mismatch between the Si₃N₄ fiber and the matrix, degrades the flexural and compressive strengths. Moreover, this excessive bonding restricts interfacial debonding and fiber pull-out, leading to a brittle fracture mode. Despite differences in interfacial microstructure, all three composites exhibit good dielectric properties. The use of SiO₂ and BN matrices effectively reduces both the dielectric constant and the dielectric loss tangent of Si₃N₄ fiber-reinforced ceramic composites. These findings provide valuable insights into the design of high-temperature wave-transparent composites operated in extreme environments.

Thermal and environmental barrier coatings play a crucial role in protecting high-temperature structural components in gas turbine engines. As turbine inlet temperatures continue to rise, corrosion challenges posed by dust, volcanic ash, and other particulate matter—collectively known as CMAS—have become increasingly severe. Understanding the reaction mechanisms between CMAS and these coatings, identifying the key factors influencing CMAS corrosion, and developing methods to inhibit CMAS infiltration are essential for advancing high-performance gas turbine engines. This review examines the origins of CMAS corrosion and summarizes recent research on CMAS corrosion mechanisms in thermal and environmental barrier coating materials. Additionally, the role of rare earth elements in CMAS corrosion and various strategies to mitigate CMAS effects are discussed. Finally, the review highlights potential directions for future research.

High-temperature corrosion caused by low-melting-point molten salts known as CMAS poses a critical challenge to hot-section components in gas turbine engines. The screening of CMAS corrosion-resistant RE₂SiO₅ ceramics is crucial for the development of environmental barrier coatings for SiC fiber reinforced SiC composites. Due to varying experimental methods, conditions, and CMAS corrosion evaluation approaches, there has been some controversy regarding the CMAS resistance of RE₂SiO₅ ceramics. To address this issue, we employed a high-throughput multilayer stacking method to eliminate external influences such as experimental conditions. The CMAS resistance of several rare earth silicate ceramics was investigated, which revealed the influence of rare earth elements on CMAS corrosion. It was found that the smaller the rare earth ionic radius, the less corrosion product formed. Additionally, Er₂SiO₅ exhibited the best CMAS resistance due to the shallowest penetration depth of CMAS. The results indicate that the evaluation of CMAS corrosion resistance of RE₂SiO₅ ceramics requires a comprehensive consideration of the formation ability of corrosion products, dissolution of RE₂SiO₅, and the penetration of CMAS.

Porous Si₃N₄ ceramics are promising high-temperature wave transparent materials for use as radomes or antenna windows in hypersonic aircraft. However, a trade-off between the dielectric and thermomechanical properties is still challenging. Therefore, tailoring the microstructure and properties of porous Si₃N₄ is highly important. In this work, porous Si₃N₄ ceramics with uniform and fine structures were obtained via dual-solvent templating combined with the freeze-casting method. The as-prepared porous Si₃N₄ ceramic, with 56% porosity, possesses high mechanical properties, with flexural strength and compressive strength values of 95±14.8 and 132±4.5 MPa, respectively. The uniform spherical pore structure improved the mechanical properties, and the rod-shaped Si₃N₄ grains facilitated crack deflection. The decreased pore size effectively blocks phonon transport, leading to a low thermal conductivity of only 4.2 W/(K·m). Moreover, the porous Si₃N₄ ceramic maintains a small dielectric constant of 3.3, and the dielectric loss is stable between 1.0×10⁻³–4.0×10⁻³, which guarantees its potential application in high-temperature wave-transparent components. These results significantly advanced the development of high-performance wave-transparent materials used in hypersonic aircraft.

ZrP₂O₇ is a promising wave-transparent material due to its low dielectric constant and low dielectric loss, but its inherent phase transition characteristic at approximately 300 °C limits its high-temperature application. Therefore, suppressing the phase transition is necessary for ZrP₂O₇ to serve in extremely harsh environments. In this work, introducing Ti and Hf into ZrP₂O₇ causes significant lattice distortion and an increase in entropy, both of which synergistically limit the crystal structure transformation. In addition, enhanced phonon scattering by mismatch of atomic mass and local distortion leads to a reduction in the thermal conductivity. Lattice distortions also cause changes in both bond length and tilting angle, so that (Ti_1/3Zr_1/3Hf_1/3)P₂O₇ does not undergo sudden expansion as does ZrP₂O₇. (Ti_1/3Zr_1/3Hf_1/3)P₂O₇ maintains excellent dielectric properties, which highlights it as a promising high-temperature wave-transparent material.

Low thermal conductivity, compatible thermal expansion coefficient, and good calcium- magnesium-aluminosilicate (CMAS) corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics. Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance. However, the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application. Inspired by the high entropy effect, a novel rare earth monosilicate solid solution (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ was designed to improve the overall performance. The as-synthesized (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ shows very low thermal conductivity (1.07 W·m^-1·K^-1 at 600 ℃). Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties. The thermal expansion coefficient of (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ can be decreased to (4.0-5.9)×10^-6 K^-1 due to severe lattice distortion and chemical bonding variation, which matches well with that of SiC ((4.5-5.5)×10^-6 K^-1). In addition, (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ presents good resistance to CMAS corrosion. The improved performance of (Ho_0.25Lu_0.25Yb_0.25Eu_0.25)₂SiO₅ highlights it as a promising environmental barrier coating candidate.