Environmental Barrier Coatings (EBCs) critically determine the performance of SiC ceramic matrix composites (CMCs) in high-temperature water-oxygen environments. As a key component of EBCs, the bond coat must ensure adhesion between the coating and substrate while effectively blocking the penetration of oxidizing/corrosive media to the SiC substrate. Current widely studied bond coat materials, such as Si and Si+HfO₂, are limited by the relatively low melting point of Si (~1410 ℃), restricting their upper service temperature. Oxide materials with higher melting points and inherent oxidation resistance have emerged as promising candidates for high-temperature bond coats. This article reviews the research progress on oxide-based bond coats, including mullite, SiO₂-HfO₂, HfO₂-Al₂O₃-SiO₂, cordierite and Yb₂Si₂O₇, focusing on their fabrication techniques, material properties and oxidation/corrosion resistance. Among these, mullite and SiO₂-HfO₂ systems demonstrate significant application potential under specific conditions. Building on these findings, this work further addresses challenges in oxide bond coats, such as brittleness, controllable synthesis, limited oxidation resistance and interfacial bonding strength. The analysis provides foundational insights and guidance for the design, development, and performance optimization of next-generation oxide-based bond coats for ultra-high-temperature environments (≥1400 ℃).

The protective effectiveness of environmental barrier coatings (EBCs) for SiC-based composites is limited by the thickening and phase transformation of the SiO₂ scale, known as thermally grown oxide (TGO). In this study, a tri-layered TGO scale, comprising cristobalite, Hf-doped SiO₂ glass, and particle-reinforced Hf–Si–O glass, was formed during the oxidation of MoSi₂/HfO₂ duplex EBCs. The incorporation of gradient Hf doping and HfO₂/HfSiO₄ particle reinforcement effectively suppressed the crystallization and phase transition of SiO₂ and mitigated the internal stress within the EBCs, generating a crack-blocking effect. This effect prevented the scale of the TGOs from further channel crack propagation, enabling the SiC substrate with no detectable corrosion after 200 h of exposure at 1500 °C in steam, even when the TGOs thickness reached 24.5 μm. This work presents a novel strategy to simultaneously extend the service lifetime and enhance the high-temperature capability of EBCs through the tailored design of TGO composition and structure.

The unique multilayer, multiscale structure of teakwood results in excellent mechanical and long-term environmental stability, providing inspiration for the biomimetic design of environmental barrier coating (EBC) structures. However, achieving the desired biomimetic structure control in high-temperature plasma spraying is a challenging task that requires new technological breakthroughs. In this study, a multiscale nano Yb₂Si₂O₇–Yb₂SiO₅ (YbDS–YbMS) composite EBC with a teakwood-like lamellar structure was realized via a novel alternating vapor/liquid phase deposition method involving plasma spraying-physical vapor deposition (PS-PVD). Volatilized waste SiO₂ from Yb₂Si₂O₇ (YbDS) was reused and deposited on the coating surface during the spraying process, where a regularly arranged multilayer structure was formed in the coating by the alternate deposition of gaseous SiO₂ and droplet YbDS. In addition, SiO₂ on the coated surface formed nanoclusters and dome-shaped nanocrystals via homogeneous and heterogeneous nucleation, respectively, and some of them gradually formed a continuous nanofilm as the arc current increased. The deposited SiO₂ reacted in situ with the decomposed phase YbMS in the coating to form YbDS, preserving its multiscale nanostructure after heat treatment and enabling the preparation of the YbDS–YbMS composite coating. This work provides a new design strategy and method for the preparation of coatings using YbDS and other spray powders with similar decomposition and volatilization characteristics during the plasma spraying process.

Fabricating SiC ceramics via the digital light processing (DLP) technology is of great challenge due to strong light absorption and high refractive index of deep-colored SiC powders, which highly differ from those of resin, and thus significantly affect the curing performance of the photosensitive SiC slurry. In this paper, a thin silicon oxide (SiO₂) layer was in-situ formed on the surface of SiC powders by pre-oxidation treatment. This method was proven to effectively improve the curing ability of SiC slurry. The SiC photosensitive slurry was fabricated with solid content of 55 vol% and viscosity of 7.77 Pa·s (shear rate of 30 s⁻¹). The curing thickness was 50 μm with exposure time of only 5 s. Then, a well-designed sintering additive was added to completely convert low-strength SiO₂ into mullite reinforcement during sintering. Complex-shaped mullite-bond SiC ceramics were successfully fabricated. The flexural strength of SiC ceramics sintered at 1550 ℃ in air reached 97.6 MPa with porosity of 39.2 vol%, as high as those prepared by spark plasma sintering (SPS) techniques.