To explore the ablation behavior of C/C-ZrC-SiC composites in extreme environments, a comparative investigation was conducted under oxyacetylene, plasma, and plasma-solid particle erosion. Results showed the composites remained intact and exhibited good long-term oxyacetylene ablation resistance. This was attributed to the predominance of thermochemical ablation under such oxygen-enriched conditions, which facilitated the formation of a ZrO2-SiO2 multilayer barrier to oxygen. Mechanical erosion became dominant for plasma and plasma-solid particle environments characterized by low oxygen content and intense scouring, degrading the ablation performance due to the cracking and spalling of surface oxides under the erosion of air flow and particles.

Given the diverse requirements of thermal protection systems for C/C composites, achieving a simultaneous enhancement of ablative and mechanical properties while ensuring lightweight is a great challenge. Recent research has discovered the development of a gradient structure has the potential to achieve multiple performance improvements simultaneously. Herein, we designed gradient C/C-ZrC-SiC composites by reactive melt infiltration and chemical vapor infiltration. The gradient structured C/C-ZrC-SiC composites achieve good shear strength of 62 MPa, revealing an increase of 26.3 % compared to the traditional C/C-ZrC-SiC composites. After ablation at 3000 degrees C for 60 s, the composites also show good ablation properties with linear and mass ablation rates of 2.37 mu m/s and 2.07 mg/s, respectively, which is attributed to the synergistic effect of oxygen resistance of the dense oxide layer and heat transfer of the pyrolytic carbon network in gradient structure.

The preparation and ablation resistance of special-shaped components have attracted considerable attention in thermal protection applications. Here we develop Cf/ZrB2-ZrC-SiC sharp leading edge composites by precursor infiltration and pyrolysis combined with reactive melt infiltration, the microstructure and ablation behavior of the composites were investigated. The B2O3 glass generated by the preferential oxidation of ZrB2 during the ablation can not only repair the defects and reduce the surface temperature, but also promote the melting and sintering of ZrO2, thereby enhancing the stability of the oxide layer. Resultantly, the Cf/ZrB2-ZrC-SiC composites with 6.67 wt% ZrB2 remains intact and presents good ablation resistance after ablation for 120 s, whose linear and mass ablation rates are reduced by 63% and 57%, respectively compared with Cf/ZrC-SiC composites. This work provides a promising strategy for constructing a sharp leading edge component for the application of thermal protective materials.

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The development of advanced aircraft relies on high performance thermal-structural materials, and carbon/carbon composites (C/C) composited with ultrahigh-temperature ceramics are ideal candidates. However, the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix. Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi2, C/C-ZrB2-ZrC-SiC composites prepared by the vacuum infiltration of ZrB2 combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases. The mass and linear ablation rates of the C/C-ZrB2-ZrC-SiC composites were respectively 68.9% and 29.7% lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration. The ablation performance was improved because the volatilization of B2O3, removes some of the heat, and the more uniformly distributed ZrO2, that helps produce a ZrO2-SiO2 continuous protective layer, hinders oxygen infiltration and decreases ablation.

With the upgrade of aircraft and the increasingly harsh service environment, it is urgent to develop highperformance thermal structural materials. In this study, inspired by foliar and root water uptake of trees, we propose a one-step facile method to achieve an autonomous gradient in C/C-ZrC-SiC sharp leading edge composites. The gradual increase of SiC content from top to bottom is beneficial to improve the heat transfer capacity of the composites. After oxyacetylene ablation for 60 s, the mass and linear ablation rates of the samples with gradient structure are 0.83 mg/s and 0.5 mu m/s, 35% and 83 % lower than conventional samples. The composites with gradient structure of ZrC and SiC are favorable to the formation of a compact and smooth ZrO2 oxide protective layer, which not only protects the composites from further penetration of O2, but also resists the mechanical denudation. The novel gradient structure composites with enhanced ablation resistance show a bright application prospect in next-generation thermal protection systems.

To mitigate interphase degradation and improve the mechanical and ablation properties of leading edge shaped C/C-ZrC-SiC composites fabricated by reactive melt infiltration, a tailored SiC-C interphase composed of SiC, gas pyrolysis carbon and phenolic resin pyrolysis char was introduced. The SiC-C interphase can effectively protect the carbon fiber from high-temperature melt erosion, improving the flexural strength of the composites by 98%. The mass and thickness change rates of the leading edge composites were 2.96 +/- 0.04 mu m/s and - 0.42 +/- 0.04 mg/s, respectively. The better ablation performance was attributed to the synergistic effect of dense and stabilized Zr-Si-O oxide layer formation and heat transfer.

C/C-SiC-HfC composites were fabricated by using Precursor Infiltration and Pyrolysis (PIP) combined with Gaseous Silicon Infiltration (GSI) process. Different GSI temperatures (1900 ℃ and 2100 ℃) were selected. The combination of PIP and GSI could significantly reduce the preparation time of the composites. The morphology displaying a rich-Si layer was formed on the surface of the composites prepared at GSI 2100 ℃. Ablation performance of the composites was investigated by oxyacetylene torch. The results showed that after ablation for 120 s, compared to the composites prepared by PIP+1900 ℃ GSI, the linear and mass ablation rates of the composites fabricated by PIP+2100 ℃ GSI were decreased from 8.05 μm/s to 5.06 μm/s and from 1.61 mg/s to 1.03 mg/s, respectively. The coverage of the rich-Si surface layer promoted the generation of more SiO2 during ablation, which not only benefited for decreasing the surface temperature but also contributed to the formation of H-Si-O glass and the HfO2 skeleton, thus better resisting the denudation of the oxyacetylene torch.

To enhance the ablation resistance of carbon/carbon composites, WSi2 modified HfB2-SiC coating was prepared by slurry dipping combined with vapor silicon infiltration. The effect of WSi2 contents on the ablation perfor-mance of the coating was investigated. The results showed that the coating with 20 wt% WSi2 had the best ablation resistance under oxyacetylene torch. During ablation, a dense Hf-Si-W-O oxide layer was covered on the coating surface, inhibiting the diffusion of oxygen. Additionally, WSi2 with high emissivity and the formed W with good thermal conductivity played a role in reducing the ablation temperature. These effects contributed to the improvement of ablation performance.

The sharp leading-edge C/C-ZrC-SiC composites with different curvature radii were obtained by reactive melt infiltration, and their ablation behaviors were investigated using an oxyacetylene torch at a heat flux of 2.4 MW/ m2 for 60 s. As the radius increased from 1 to 2 mm, the linear change rates decreased from 2.82 to -3.67 mu m/s. Samples with smaller radius tended to suffer from more severe ablation under higher temperatures, thermal stress, strong gas erosion and the decrease of oxide layer stability are responsible for the ablation degradation of the composites.

To explore the effect of the strain rates on ZrC/C composites, their interface evolution, impact behavior and electrical performance under different impact speeds were studied. As the strain rate increased from 206 s(-1) to 1402 s(-1), the compressive strength of the ZrC/C composites first increased by 40.9% (375.8 +/- 22.5 MPa) and then decreased by 20.3%. Compared with the electric resistance of the ZrC/C composites before impact, their electric resistance increased by 76.7% after impact under the strain rate of 206 s-1. As the ZrC/PyC weight ratio increased from 1.4 to 2.6, the hardness of the ZrC/C composites increased from 143.2 +/- 15.7 HV to 298.6 +/- 18.5 HV, and their modulus increased from 14.6 +/- 1.8 GPa to 26.3 +/- 1.9 GPa. The finite element simulation results showed that appropriately increasing the relative ceramic content can improve the impact resistance of the ZrC/C composites. This work provides an effective strategy for optimizing the impact resistance of ultra-high temperature composites by controlling the relative ceramic content.