To enhance the resistance of SiC_f/SiC to hydrothermal corrosion in the pressurized water reactor (PWR) environment, structurally tunable Ti₃SiC₂-based corrosion mitigation coatings for SiC_f/SiC were prepared using molten salt synthesis. The influence of various process parameters, such as Si/Ti molar ratio in raw materials, annealing time, and annealing temperature, on the phase composition and the structure of the coatings was explored. Through the process control, the fabricated coatings can be either Ti₃SiC₂ monolithic structure or TiC/Ti₃SiC₂ and TiC/Ti₃SiC₂/Ti₅Si₃C_x multi-layered structures. The coatings demonstrate strong bonding to the substrate due to in-situ reaction, exhibiting tensile and shear strength of at least 26.9 and 30.8 MPa, respectively. Incorporating TiC as a transition layer further enhances the tensile and shear strength to 41.3 and 51.4 MPa, respectively. Monolithic Ti₃SiC₂ coatings enhance the thermal conductivity of SiC_f/SiC by 10%–12%. Notably, Ti₃SiC₂ coatings effectively protect SiC_f/SiC from hydrothermal corrosion, demonstrating an 83% strength retention rate compared to 71% in the control group after corrosion. However, the Ti₅Si₃C_x layer exhibits unsatisfactory corrosion mitigation. The Ti₃SiC₂ monolithic coating has higher thermal conductivity, TiC/Ti₃SiC₂ multi-layered coating has higher bonding strength, and both have desirable resistance to the hydrothermal corrosion.

Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite (CMC-SiC), which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment. As for some thermal-structure components with low working stress, improving the degree of densification was crucial to prolong the service life, and the related process approaches were recited. If the thermal-structure components worked under moderate stress, the matrix cracking stress (σ_mc) should be improved as far as possible. The fiber preform architecture, interface shear strength, residual thermal stress, and matrix strengthening were associated with σ_mc in this review. Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours. The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen. The effective self-healing temperature range of different self-healing components was first summarized and distinguished. The structure, composition, and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.

The microstructure of polymer-derived ceramics (PDCs) was closely related to processing. This study demonstrated that SiCN matrix prepared by polymer infiltration and pyrolysis (PIP) at 900 ℃ inside a Si₃N₄ whisker (Si₃N_4w) preform with submicro-sized pores differed from its powder- consolidated analogue in both the content and structure of free carbon. Chemical analysis showed that PIP process had a higher free carbon yield. Raman spectroscopy and transmission electron microscopy (TEM) observation discovered a higher graphitization degree of free carbon and the existence of nanocrystalline graphite in SiCN matrix. Dielectric properties of Si₃N_4w/SiCN composites were greatly enhanced when volume fraction of SiCN matrix reached 24.5% due to dielectric percolation caused by highly-lossy free carbon. Reconsolidation of hydrocarbon released during pyrolysis by gas-state carbonization in Si₃N₄ whisker preform was supposed to account for the high yield and graphitization degree of free carbon in PIP process.

The SiBCN matrix via chemical vapor infiltration (CVI) or/and polymer infiltration pyrolysis (PIP) technologies was orderly introduced to SiC_f/SiC composites to optimize the mechanical property and electromagnetic (EM) shielding effectiveness simultaneously. The BN interface with the thickness of 350 nm was designed to obtain a little stronger interface bonding. The flexural strength of SiC_f/SiC-SiBCN composites reached 545.45±29.59 MPa thanks to the crack deflection between the CVI SiC and CVI SiBCN, as well as CVI SiBCN and PIP SiBCN matrix because of the modulus difference between them. The fracture toughness (K_IC) with the value of 16.02±0.94 MPa·m^1/2 was obtained owing to the extension of crack propagation path. The adverse effect of stronger interface bonding was eliminated by the design of matrix microstructure for SiC_f/SiC-SiBCN composites. The thermal conductivity in the thickness direction was 7.64 W·(m·K)^-1 at 1200 ℃ and the electric resistivity decreased to 1.53×10³ Ω·m. The tunable dielectric property was obtained with the coordination of wave-absorption CVI SiBCN matrix and impedance matching PIP SiBCN matrix, and the total shielding effectiveness (SE_T) attained 30.01 dB. It indicates that the SiC_f/SiC-SiBCN composites have great potential to be applied as structural and functional materials.