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.

Si₃N₄ fiber-reinforced ceramic composites are promising candidates for high-temperature wave-transparent applications, yet the relationships among composition, interface 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. Results reveal that reaction between BN precursors and silanol groups in the SiO₂ matrix during the fabrication of Si₃N_4f/SiO₂-BN enhance the chemical compatibility between 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 3.73 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 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.

High-entropy carbide ceramics (HECCs) are promising ultrahigh-temperature ceramics with exceptional properties, but their brittleness limits their practical application. Inspired by the structure of bamboo, fibrous monolithic high-entropy (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-based ceramics (FMCs) with continuous weak cell boundaries were designed and fabricated through a combination of phase inversion and hot-pressing techniques. By optimizing the composition of the cell boundary, FM721 achieves a high fracture toughness of 8.3±1.5 MPa∙m^1/2, a 51.9% improvement over (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C (HECC), and a work of fracture of 784.0±190.8 J/m², a 1132.7% increase. The toughening mechanisms include crack deflection, crack branching, and load redistribution at the cell boundary, which increase the crack propagation path, consuming more energy. Moreover, the introduction of cell boundaries reduces the defect sensitivity and enhances damage tolerance. For example, FM721 maintains 77.8% of its initial flexural strength even after a 294 N indentation. Moreover, the relatively low density of FMCs and the thermal barrier effect at the cell boundaries significantly enhance the thermal insulation performance. As the temperature increases from room temperature (25 °C) to 1000 °C, the thermal conductivity of FM721 decreases by 22.9% and 34.5%, respectively, compared with that of the conventional HECC. This work presents a novel strategy for optimizing both the mechanical strength and thermal insulation performance of HECCs, providing insights for the design of thermal protection materials in extreme environments.

For Bi₄Ti₃O₁₂ (BIT) high-temperature piezoceramics, improving piezoelectric performance often comes at the expense of a reduced Curie temperature. In this study, a series of Bi_4−xCe_xTi_2.97(Cr_1/3Ta_2/3)_0.03O₁₂ (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were synthesized using the solid-state reaction method, and their phase structure, microstructure, piezoelectric properties, and conduction mechanisms were systematically analyzed. By employing a B-site non-equivalent co-doping strategy and introducing Ce ions into the A-site, we achieve a synergistic increase in the piezoelectric performance, Curie temperature, and high-temperature resistivity of BIT-based ceramics. This A/B site multi-co-doping significantly enhances the electrical properties by reducing the oxygen vacancy concentration. Notably, the ceramics with x = 0.04 exhibit a high piezoelectric coefficient (d₃₃) of 37 pC·N⁻¹, excellent resistivity of 6.6×10⁶ Ω·cm at 500 °C, and a high Curie temperature of 681 °C. Piezoelectric force microscopy and phase field simulation reveal that the superior piezoelectric performance arises from larger domain sizes, a stronger response to external electric fields, and a higher breakdown field strength. These findings not only position this material as a robust candidate for high-temperature applications but also provide valuable insights into the design of piezoelectric ceramics with enhanced stability and performance.

Electrobending, an emerging phenomenon in electroactive ceramics, has recently attracted significant interest; however, existing measurement methods often confound electrotensile and electrobending strains, leading to ambiguity. This study distinguishes electrotensile and electrobending strains in K_0.5Na_0.5NbO₃ (KNN) ceramics by examining their thickness, frequency, temperature, and directional dependency, identifying a critical thickness threshold of 600 μm for electrobending in samples of 8.5 mm diameter. This threshold establishes a clear distinction between electrotensile and electrobending within the KNN system and provides a benchmark that can be applied to other systems through similar methodologies. Additionally, new electrobending parameters have been defined to assess bending deformation, addressing recent misinterpretations of “giant strain” and advancing electrostrain research by introducing an electrobending framework.

Si₃N₄ ceramics are promising wave-transparent materials with excellent mechanical and dielectric properties. Vat photopolymerization (VPP) three-dimensional (3D) printing provides a strategy for preparing ceramics with controllable complex structures. However, the difficulty in solidifying the slurry due to partial ultraviolet (UV) light absorption and the high refractive index of Si₃N₄ particles during the VPP process severely hinder the molding of Si₃N₄ ceramics. A higher laser power must be used to increase the curing depth, which generates large internal stresses and warps the samples. This study presents a method to solve the warpage problem during VPP-3D printing using tributyl citrate as a plasticizer. The plasticizer can weaken the force between polymer molecular chains and reduce the internal stress of the green body. Warpage decreases gradually with increasing tributyl citrate content, and the warpage decreases to 0% when the plasticizer content reaches 30 wt% at high laser powers from 600 to 750 mW. Samples with different layer thicknesses were printed, and the optimum thickness of 40 μm was obtained, at which the sintered Si₃N₄ samples possessed a unique combination of mechanical properties, including a bending strength of 338.29±12.08 MPa and a fracture toughness of 6.94±0.11 MPa·m^1/2 for the loading direction perpendicular to the build surface and 5.37±0.99 MPa·m^1/2 for the loading direction parallel to the build surface. The dielectric constant of all the samples is maintained in the range of 5.462–6.414. This work is expected to guide vat photopolymerization and the preparation of complex Si₃N₄ ceramic components.

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.

In this study, (Cr_1/3/Ta_2/3) non-equivalent co-doped Bi₄Ti₃O₁₂ (BIT) ceramics were prepared to solve the problem that high piezoelectric performance, high Curie temperature, and high-temperature resistivity could not be achieved simultaneously in BIT-based ceramics. A series of Bi₄Ti_3−x(Cr_1/3Ta_2/3)_xO₁₂ (x = 0–0.04) ceramics were synthesized by the solid-state reaction method. The phase structure, microstructure, piezoelectric performance, and conductive mechanism of the samples were systematically investigated. The B-site non-equivalent co-doping strategy combining high-valence Ta⁵⁺ and low-valence Cr³⁺ significantly enhances electrical properties due to a decrease in oxygen vacancy concentration. Bi₄Ti_2.97(Cr_1/3Ta_2/3)_0.03O₁₂ ceramics exhibit a high piezoelectric coefficient (d₃₃ = 26 pC·N⁻¹) and a high Curie temperature (T_C = 687 ℃). Moreover, the significantly increased resistivity (ρ = 2.8×10⁶ Ω·cm at 500 ℃) and good piezoelectric stability up to 600 ℃ are also obtained for this composition. All the results demonstrate that Cr/Ta co-doped BIT-based ceramics have great potential to be applied in high-temperature piezoelectric applications.

Rare earth (RE) silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines. However, calcium–magnesium–alumina–silicate (CMAS) corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature. Therefore, it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures. Herein, the interaction between RE₂SiO₅ and CMAS up to 1500 ℃ was investigated by a novel high-temperature in-situ observation method. High temperature promotes the growth of the main reaction product (Ca₂RE₈(SiO₄)₆O₂) fast along the [001] direction, and the precipitation of short and horizontally distributed Ca₂RE₈(SiO₄)₆O₂ grains was accelerated during the cooling process. The increased temperature increases the solubility of RE elements, decreases the viscosity of CMAS, and thus elevates the corrosion reaction rate, making RE₂SiO₅ fast interaction with CMAS and less affected by RE element species.