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In this study, a Cf/Ta4HfC5‐SiC ultra‐high‐temperature ceramic matrix composite exhibiting a homogeneous phase distribution was successfully fabricated via precursor infiltration and pyrolysis processing. Initially, the pyrolysis and solid solution mechanisms exhibited by the Ta4HfC5 precursor were investigated and characterized through TG‐MS and XRD analysis. The as‐fabricated Cf/Ta4HfC5‐SiC composite exhibited a density and open porosity of 2.84 g/cm3 and 10.62 vol%, respectively. It also exhibited outstanding mechanical properties, with a flexural strength of 339 ± 20 MPa and fracture toughness of 11.56 ± 0.77 MPa·m1/2. The Cf/Ta4HfC5‐SiC composite demonstrated strong ablation resistance under a heat flux of 5 MW/m2 at ~2400℃, with corresponding linear and mass recession rates of 5.33 μm/s and 6.18 mg/s, respectively. The combination of strong mechanical properties and ablation resistance provides a solid basis for the use of the Cf/Ta4HfC5‐SiC composite in a new generation of ultra‐high‐temperature materials. [ABSTRACT FROM AUTHOR]

In this work, 3D-C f /HfC-SiC-based composites were fabricated and optimized via reactive melt infiltration (RMI) of Si into porous C f /HfC-C preforms prepared by a sol-gel processing. The physical and chemical processes involved during the fabrication were identified and analyzed in details. It is revealed that fibers and interphase of the composites can be eroded during carbothermal reduction process, which can be further aggravated during RMI, with the formation of Hf-containing substance on the fibers surface. The fibers and interphase degradation is mainly induced by the reactions between HfO 2 and C/SiC interphase layers at elevated temperatures. Accordingly, a two-step carbothermal reduction treatment was proposed for the optimization of the fabrication procedure. As a result, less fiber/interphase erosion and improved mechanical properties are achieved in the composites, with the bending strength increased by ∼49 % (from 214.1 ± 15.7 MPa to 319.0 ± 26.0 MPa). [ABSTRACT FROM AUTHOR]

Layer-structured interphase, existing between carbon fiber and ultrahigh-temperature ceramics ( UHTCs) matrix, is an indispensable component for carbon fiber reinforced UHTCs matrix composites (Cf/ UHTCs). For Cf/ UHTCs fabricated by reactive melt infiltration ( RMI), the interphase inevitably suffers degradation due to the interaction with the reactive melt. Here, Cf/SiC-ZrC-ZrB2 composite was fabricated by reactive infiltration of ZrSi2 melt into sol-gel prepared Cf/B4C-C preform. (PyC-SiC)2 interphase was deposited on the fiber to investigate the degradation mechanism under ZrSi2 melt. It was revealed that the degraded interphase exhibited typical features of Zr aggregation and SiC residuals. Moreover, the Zr species diffused across the interphase and formed nanosized ZrC phase inside the fiber. A hybrid mechanisms of chemical reaction and physical melting were proposed to reveal the degradation mechanism according to characterization results and heat conduction calculations. Based on the degradation mechanism, a potential solution to mitigate interphase degradation is also put forward. [ABSTRACT FROM AUTHOR]

For the first time, air plasma ablation behavior of C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C–SiC high-entropy ceramic matrix composites was studied systematically under a heat flux of 5 MW/m2, which provided a quasi-real hypersonic service environment at a temperature up to 2430 °C. The C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C–SiC composites present excellent ablation-resistant performance with a linear recession rate of ∼2.89 μm/s and mass recession rate of ∼2.60 mg/s, which can be attributed to the dense and stable oxides layer formed on the sample surface. (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C is oxidized to high-entropy oxide (TiZrHfNbTa)O x at the ablation center and highly viscous SiO 2 melt with uniformly dispersed (TiZrHfNbTa)O x microspheres is formed. While at the edge of the ablation center, precipitation occurs during cooling and the oxides layer turns to a plate-like (Hf 0.5 Zr 0.5 O 2)' skeleton surrounded by (TiNbTaO 7-y)' nanocrystals and continuous SiO 2 melt. In contrast, oxidation of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C to produce (Hf 0.5 Zr 0.5 O 2)' and (TiNbTaO 7-y)' is dominant at the ablation transition area and outer area with lower temperature. The multiphase oxides formed during ablation provide a stable and highly self-healing protective layer for the internal materials at ultra-high temperatures. [ABSTRACT FROM AUTHOR]