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Pitch-based short carbon fibres reinforced C sf /ZrB 2 -SiC composites were fabricated by direct ink writing of short carbon fibres, followed by slurry impregnation and reactive melt infiltration. Ablation behaviour of the C sf /ZrB 2 -SiC composite was studied by air plasma test. It is indicated that the skeleton of the oriented short carbon fibres provides heat diffusion channels. Consequently, temperatures at the ablation surface are as low as ∼1730 oC and ∼2000 oC respectively at 4 MW/m2 and 5 MW/m2. The composite presents outstanding ablation-resistant performance with a linear recession rate of ∼ − 0.04 µm/s and mass recession rate of ∼ − 3.40 mg/s at 4 MW/m2, ∼ − 0.17 µm/s and ∼ 3.58 mg/s at 5 MW/m2. It is revealed that the fibres area and matrix area of the composite present different ablation mechanisms. The fibres area is ablated severely, while the matrix area presents excellent ablation-resistance with continuous ZrO 2 -SiO 2 protective layer. [ABSTRACT FROM AUTHOR]

In this work, ablation behavior and mechanisms of 3D-C f /Ta 0.8 Hf 0.2 C-SiC composite were studied via air plasma test at temperatures up to 2500 °C. At temperatures below 2000 °C, a continuous oxides layer composed of o -Ta 2 O 5(H) – t -Ta 2 O 5 – Hf 6 Ta 2 O 17(H) – SiO 2 is formed on the ablation surface, which turns to o -Ta 2 O 5(H) – SiO 2 above 2200 °C. During ablation, o -Ta 2 O 5(H) precipitates from the glassy SiO 2 and grows up following Oswald ripening. Although the volatilization of SiO 2 aggravates with ablation temperature increase and ablation time extension, o -Ta 2 O 5(H) – SiO 2 melt can still serve as effective self-healing similar to SiO 2 glass. Accordingly, the multiphase oxides layer formed on the ablation surface provides a stable protective effect for the internal composite under all the tested ablation conditions. As a consequence, the 3D-C f /Ta 0.8 Hf 0.2 C-SiC composite presents outstanding ablation-resistant performance even at 2500 °C for 300 s, with a linear recession rate of ∼ 5.7 µm/s and a mass recession rate of 2.91 mg/s. [ABSTRACT FROM AUTHOR]

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]

• C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC high-entropy ceramic matrix composites were reported for the first time. • The pyrolysis and the solid-solution mechanisms of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C precursor were systematically studied. • The as-fabricated C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites present excellent mechanical and anti-ablation properties. In this work, C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC high-entropy ceramic matrix composites were reported for the first time. Based on the systematic study of the pyrolysis and solid-solution mechanisms of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C precursor by Fourier transform infrared spectroscopy, TG-MS and XRD, C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC with uniform phase and element distribution were successfully fabricated by precursor infiltration and pyrolysis. The as-fabricated composites have a density and open porosity of 2.40 g/cm3 and 13.32 vol% respectively, with outstanding bending strength (322 MPa) and fracture toughness (8.24 MPa m1/2). The C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites also present excellent ablation resistant property at a heat flux density of 5 MW/m2, with linear and mass recession rates of 2.89 μm/s and 2.60 mg/s respectively. The excellent combinations of mechanical and ablation resistant properties make the C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites a new generation of reliable ultra-high temperature materials. [ABSTRACT FROM AUTHOR]

In this study, short carbon fibre (C sf) reinforced ZrB 2 -SiC composites were fabricated via direct ink writing followed by precursor infiltration and pyrolysis. The ablation behaviour of the composites was investigated at heat fluxes of 4–6 MW/m2 under an air plasma flame, which revealed excellent ablation resistance with negative linear ablation rates of − 0.1 to − 0.5 µm/s. The results showed that ZrO 2 -SiO 2 oxide layer was formed on the ablation surface after ablation, which provided effective protection to the internal materials. With an increase in heat flux, ZrO 2 precipitated from the SiO 2 melt first in the form of nano-tetragonal ZrO 2 (t -ZrO 2), owing to the vaporisation of SiO 2. During cooling, the nano t -ZrO 2 particles were retained, and some of them reacted with SiO 2 to form ZrSiO 4 , thus improving the thermal stability of the SiO 2 -ZrO 2 oxide layer. In contrast, t -ZrO 2 agglomerated and grew owing to capillary force and finally transformed into monoclinic ZrO 2 (m -ZrO 2). Moreover, a higher heat flux led to the size of precipitation ZrO 2 increases, meanwhile increasing the content of t -ZrO 2 and ZrSiO 4 in the oxide layer. • Short carbon fibers reinforced C sf /ZrB 2 -SiC composites were fabricated by direct ink writing, followed by precursor impregnation and pyrolysis. • During cooling, the nano t -ZrO 2 particles were retained, and some of them reacted with SiO 2 to form ZrSiO 4 , thus improving the thermal stability of the SiO 2 -ZrO 2 oxide layer. • The capillary force leads to the nano crystals gradually agglomerate and form dendritic structure. • From 4 to 6 MW/m2, the size of the dendritic structure ZrO 2 increased. [ABSTRACT FROM AUTHOR]

Ablation behavior of 3D-C f /SiBCN composites with (PyC/SiC) 3 multi-layers as interphase was investigated in plasma ablation flame at a heat flux of 4.02 MW m−2. During ablation, amorphous SiBCN matrix is firstly oxidized and forms a borosilicate glass, in which B 2 O 3 is volatilized as the ablation going on. At the ablation center with higher temperature, SiC and Si 3 N 4 grains are precipitated from the amorphous SiBCN matrix. And then, these SiC and Si 3 N 4 grains are oxidized, forming a certain viscous silica rich protective coating on the sample surface. Moreover, it is revealed that the SiC layers in (PyC/SiC) 3 multi-layers interphase can protect the carbon fibers from ablation damage effectively. Compared with the C f / (PyC) SiBCN composites, much improved ablation resistance is achieved for the C f / (PyC/SiC)3 SiBCN composites. The linear and mass recession rates of the C f / (PyC/SiC)3 SiBCN composites are as low as 1.7 ± 0.4 μm s−1 and 0.0427 ± 0.0053 mg mm−2s−1, which are ∼43 % and ∼21 % lower than those of C f / (PyC) SiBCN. [ABSTRACT FROM AUTHOR]

• The difference of ablation behavior for ZrC- and ZrB 2 -based coatings was firstly investigated and reported. • ZrB 2 -based coating showed better ablation resistance including lower surface temperature and superior oxidation resistance. • The ablation mechanism of ZrC- and ZrB 2 -based coatings was also analyzed based on thermodynamics predictions. In the present work, five kinds of UHTCs coatings (ZrC, ZrC-SiC, ZrB 2 , ZrB 2 -SiC, ZrB 2 -ZrC-SiC) were fabricated. The difference of ablation behavior between ZrB 2 - and ZrC-based coatings was evaluated and focused on. The microstructure evolution of resulted oxide layer were characterized in detail. The results showed that the ablation resistance of ZrB 2 -based coating was better than that of ZrC-based coating under the same environment, exhibiting lower surface temperature, thinner thickness of both the total oxide layer and the SiC-depleted layer. The possible reasons for the phenomena were supposed based on microstructure characters and thermodynamic analysis. [ABSTRACT FROM AUTHOR]