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In this work, an efficient processing route was developed to fabricate C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites via slurry infiltration lamination (SIL) combined with precursor infiltration and pyrolysis (PIP). The (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C powder was initially synthesized at 1900 °C. Then the 2D C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites were obtained via SIL and PIP at temperatures no higher than 1100 °C. The as-fabricated composites show a density of 2.52 g/cm3 and an open porosity of 15.2 vol%, with a bending strength of 255 ± 15 MPa. The 2D C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites also present excellent ablation resistance, with the linear and mass recession rates of 0.33 µm/s and 0.60 mg/s after ablation at 2000 °C/300 s. This work provides a route for the efficient fabrication of C f /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C-SiC composites, and also inspires new strategies to develop high-entropy ceramic matrix composites with high performance. [ABSTRACT FROM AUTHOR]

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]

• 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 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]

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]

C/C-ZrC and C/SiC-ZrC composites were fabricated by a joint process of slurry impregnation and chemical vapor infiltration, in which ZrC matrix was obtained by slurry impregnation process, while C or SiC matrix was introduced by chemical vapor infiltration process. The as fabricated C/C-ZrC and C/SiC-ZrC composites have densities of 1.67 g cm −3 and 1.91 g cm −3 respectively. Tensile strength is 89.4±8.4 MPa and 182.2±14.0 MPa respectively for the as prepared C/C-ZrC and C/SiC-ZrC. Ablation behavior of the C/C-ZrC and C/SiC-ZrC composites under air plasma was studied and compared in detail. Due to different oxidation resistance and heat transfer capacity of the matrix, these two ZrC based composites showed various ablation behavior. The linear erosion rate is 48 µm s −1 and 39 µm s −1 respectively for C/C-ZrC and C/SiC-ZrC composites. [ABSTRACT FROM AUTHOR]

Reaction bonded B 4 C-SiC composites were prepared by infiltrating silicon melt into porous B 4 C-SiC green preforms at 1500 °C in vacuum. The porous green preform was obtained from a mixture of polycarbosilane (PCS) and particle size graded B 4 C after pre-sintering at 1600 °C. For the first time, PCS was used to adjust the phase composition and microstructure of the reaction bonded boron carbide composites. It is indicated that the addition of PCS and its content has a significant influence on the microstructure as well as the mechanical properties of the subsequent reaction bonded B 4 C-SiC composites. For the B 4 C-SiC composite with 5 wt% PCS added, a flexural strength of 319±12 MPa, and an elastic modulus of 402±18 GPa can be achieved, which is 23% and 15% higher than those of the composite without PCS addition, respectively. While, with the higher content of PCS addition, the mechanical properties of the composites are decreased drastically due to the large amount of residual Si agglomeration in the composites. The reaction mechanisms as well as their microstructure evolution processes correlated with the mechanical properties of the reaction bonded B 4 C-SiC composites are further discussed in our work. [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]

• Internal C f /SiBCN composites endure severe thermal damage and complex reactions during ablation. • Thermal damage of SiBCN matrix results from crystallization and degradation of amorphous SiBCN. • Ring-like SiC is formed covering the fibers, providing further protection to the carbon fibers. Ablation behavior and thermal damage mechanisms of C f /SiBCN composites were investigated in plasma ablation flame under a heat flux of 4.02 MW/m2, simulating a hypersonic service environment at ∼2200 °C. Oxide layer formed on the composites surface effectively protects internal C f /SiBCN composites from further ablation. However, the internal C f /SiBCN composites endure severe thermal damage and complex reactions, leading to decomposition of SiBCN matrix and formation of α/β-SiC, β-Si 3 N 4 grains, amorphous C layer and ring-like SiC layer. Based on detailed microstructure and phase composition analysis, thermal damage and microstructure evolution mechanisms of C f /SiBCN composites during plasma ablation are clarified. [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]

Three-dimensional C f /SiC-ZrC-ZrB 2 composites were fabricated by a joint process of sol-gel and reactive melt infiltration. Ablation test of the composites was performed under air plasma. The composites showed negative recession rates at 1800–2000 °C, while positive recession rates above 2000 °C. Results revealed that dense SiO 2 -ZrO 2 -B 2 O 3 layer formed on the sample surface prevented the ablation process extending inward the samples. At higher temperature, active oxidation of SiC and severe evaporation of oxide phase significantly impaired the integrity of the oxide layer and inevitably deteriorated the resistance of the oxide layer to the air plasma. [ABSTRACT FROM AUTHOR]

In the present study, a novel liquid polycarbosilane (LPCS) with a ceramic yield as high as 83% was applied to develop 3D needle-punched C f /SiC composites via polymer impregnation and pyrolysis process (PIP). The cross-link and ceramization processes of LPCS were studied in detail by FT-IR and TG-DSC; a compact ceramic was obtained when LPCS was firstly cured at 120 °C before pyrolysis. It was found that the LPCS-C f /SiC composites possessed a higher density (2.13 g/cm 3 ) than that of the PCS-C f /SiC composites even though the PIP cycle for densification was obviously reduced, which means a higher densification efficiency. Logically, the LPCS-C f /SiC composites exhibited superior mechanical properties. The shorter length and rougher surfaces of pulled-out fibers indicated the LPCS-C f /SiC composites to possess a stronger bonding between matrix and PyC interphase compared with the PCS-C f /SiC composites. [ABSTRACT FROM AUTHOR]

Three-dimensional C f /SiC-ZrC-ZrB 2 composites were fabricated by reactive melt infiltration of ZrSi 2 alloys into porous C f /B 4 C-C preforms prepared through a sol-gel process. The influence of pore structure of the C f /B 4 C-C preforms on microstructure and mechanical performances of the C f /SiC-ZrC-ZrB 2 composites was studied. It was found that the microstructure and mechanical performances of the composites showed a strong dependence on the pore structure of the preforms. Residual ZrSi 2 content in the composites was significantly reduced with the decreases in the porosity and pore size of the C f /B 4 C-C preforms. At the same time, fiber erosion in the composites was also gradually mitigated, which led to a significant improvement in the fracture behaviors of the composite, as failure mode of the composites changed from brittle to pseudo-plastic. When the porosity of the preforms decreased from 53.7% to 31.3%, the flexural strength of the composites increased from 53 MPa to 184 MPa. [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]