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To improve ablation resistance of silicon carbide (SiC)-coated carbon/carbon (C/C) composites, in this study, zirconium carbide (ZrC) coating was prepared on the surface of SiC-coated C/C composites by supersonic plasma spraying. The coating exhibits dense structure, and a good bonding with substrate. The oxyacetylene ablation results show that the ZrC coating greatly improved the ablation resistance of SiC-coated C/C composites. After ablation for 30 s in oxyacetylene flame, the linear ablation rate is only 0.9 × 10 mm/s, and the weight is increased by 2.0 × 10 g/s. The excellent ablation resistance is mainly attributed to the formation of a dense and continuous zirconia (ZrO) layer during the oxidation of the ZrC coating. [ABSTRACT FROM AUTHOR]

Abstract: A MoSi2–CrSi2–SiC–Si multi-component coating was prepared on the surface of carbon/carbon (C/C) composites by a two-step pack cementation method. The microstructure, oxidation behavior and mechanical properties of the coating were studied. These results show that the multi-component coating could protect the C/C composites from oxidation in air at 1873K for 300h and withstand 30 thermal cycles between 1873K and room temperature, respectively. The mass loss and mechanical property loss of the coated C/C composites are considered due to the worse fluidity of SiO2 at intermediate temperatures and the thermal mismatch between the coating and C/C composites. [Copyright &y& Elsevier]

To improve the oxidation resistance of the SiC-MoSi2 coating prepared by two-step pack cementation, a liquid Si infiltrating method was adopted to modify it. The phase composition and microstructure of the coatings were analyzed by XRD and SEM. The results show that the size and number of the cracks in the modified coating decreased evidently after infiltrating Si. The oxidation test results in air at 1773 K show that the mass loss of the SiC-MoSi2 coating coated carbon/carbon (C/C) composites was up to 1.18% after oxidation for 206 h, while that of the modified coating coated C/C composites was only 0.77% after oxidation for 460 h. The reason is that the cracks formed in the pack cementation process were partly sealed and there were no penetrable cracks in the modified coating. Therefore, there were no direct channels for the oxygen to diffuse into the C/C substrate. [ABSTRACT FROM AUTHOR]

Abstract: To protect carbon/carbon (C/C) composites against oxidation, a Si–Mo coating was prepared on C/SiC-coated C/C composites by a simple slurry method. The microstructure of the coating was characterized by X-ray diffraction, scanning electron microscopy and Raman spectra. Results showed that the coating was mainly composed of SiC, MoSi2 and Si. It could protect C/C composites from oxidation at 1873K in air for 300h and withstand 13 thermal cycles between room temperature and 1873K. The excellent oxidation and thermal shock resistance of the coating was attributed to the formation of dense SiO2 glass at high temperature. The volatilization of MoO3 and SiO2 at 1873K was the main reason of the weight loss of the coated C/C composites. [Copyright &y& Elsevier]

Abstract: To protect carbon/carbon (C/C) composites from oxidation at elevated temperature, an effective WSi2–CrSi2–Si ceramic coating was deposited on the surface of SiC coated C/C composites by a simple and low-cost slurry method. The microstructures of the double-layer coatings were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy analyses. The coating exhibited excellent oxidation resistance and thermal shock resistance. It could protect C/C composites from oxidation in air at 1773K for 300h with only 0.1wt.% mass gain and endure the thermal shock for 30 cycles between 1773K and room temperature. The excellent anti-oxidation ability of the double-layer WSi2–CrSi2–Si/SiC coating is mainly attributed to the dense structure of the coating and the formation of stable vitreous composition including SiO2 and Cr2O3 produced during oxidation. [ABSTRACT FROM AUTHOR]

Abstract: Multi-layer MoSi2–CrSi2–Si anti-oxidation coatings with different compositional ratios were prepared on the surface of SiC coated carbon/carbon (C/C) composites by a two-step pack cementation method. The microstructure and anti-oxidation performance of the coating were studied. The results show that the multi-layered coatings could protect the C/C composites from oxidation in air at 1773K for 1000h or 1873K for 750h, respectively. The anti-oxidation performance of the multi-layer MoSi2–CrSi2–Si coating is mainly attributed to their dense and microcrack-free structure, appropriate thermal expansion coefficient and the well dispersed MoSi2 and CrSi2 in the coating. [Copyright &y& Elsevier]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation, a multilayer oxidation resistant coating was prepared. The inner SiC coating was prepared by pack cementation, and the outer SiC–MoSi2 three-layer coating was obtained by slurry coating using silicon–sol as the caking agent. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyze the phase, microstructure and element distribution of the as-prepared coating. The results show that, the as-received multilayer coating has a crack-free structure with the thickness of about 300μm. It is provided with excellent oxidation resistance from room temperature to 1500°C in air and can protect C/C composites from oxidation for more than 120h at 900°C and more than 110h at 1500°C in air. The weight loss of the coated samples during oxidation tests mainly resulted from the oxidation of Mo5Si3 and the volatilization of SiO2 in the coating. [Copyright &y& Elsevier]

Abstract: To protect carbon/carbon (C/C) composites against oxidation, a B2O3 modified SiC–MoSi2 coating was prepared by a two-step pack cementation. The microstructure and the oxidation resistant property of the coating were studied. The results show that, the as-received coating is a dense structure, and is composed of α-SiC, β-SiC and MoSi2. The B2O3 modified SiC–MoSi2 coating has excellent oxidation resistant property, and can protect C/C composites from oxidation at 1773K in air for more than 242h. The failure of the coating was considered to arise from the existence of the penetration cracks in the coating during the slow cooling from 1873 to 673K. [Copyright &y& Elsevier]

In order to protect carbon/carbon (C/C) composites against oxidation, a Si–Mo–W coating was prepared on the surface of SiC-coated C/C composites by a simple reaction method. The microstructures of the as-received coating were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy analyses. The results show that the SiC/Si–Mo–W coating can protect C/C composites from oxidation in air at 1673 K for 220 h with a mass loss of 0.003%, and at 1773 K for 252 h with a mass gain of 1.56%. The excellent oxidation-resistant property of the SiC/Si–Mo–W coating at 1673–1773 K is attributed to the formation of SiO2 film on the coating surface. The mass loss of the coated C/C composites during the oxidation test at 1873 K in air primarily resulted from the reaction of C/C substrate and oxygen diffusing through the penetration cracks in the coating. [ABSTRACT FROM AUTHOR]

Abstract: Yttrium silicates interlayer coatings of the SiC/yttrium silicates/borosilicate glass multi-layer coating system were prepared by a novel in-situ formation method using Si and Y2O3 as starting materials in an oxidation atmosphere. The surface and cross-section microstructures of the coatings were characterized by XRD and SEM analyses. Oxidation resistance of the coated samples was tested. Results showed that dense yttrium silicate interlayer coatings with good bond to SiC and borosilicate glass were prepared and the as-prepared multi-layer coating could protect C/C composites from oxidation at 1873K in air for 202h with a weight loss of 2.87×10−3g/cm2. [Copyright &y& Elsevier]

Abstract: To prevent carbon/carbon composites from oxidation at 1773 K, an efficient oxidation protective glass coating has been prepared on the surface of SiC coated C/C composites by a simple and low-cost method. The microstructures and phase composition of the as-prepared coating were examined by SEM and XRD. Oxidation testing shows, after oxidation in air at 1773 K for 140 h and thermal cycling between 1773 K and room temperature for 8 times, the weight loss of the coated sample is only 0.98%. The oxidation of the coated C/C composites is attributed to the formation of bubble holes on the coating surface and microcracks in the coating. [Copyright &y& Elsevier]

Abstract: In this work, the network structure of ZrO2 nanorods was firstly synthesized without a metal catalyst. A developed vapor–liquid–solid (VLS) and oxide-assisted growth (OAG) model is discussed as the growth mechanism of ZrO2 nanorods. ZrO2 nanoparticles, as a growth catalyst, provide zirconium and oxygen atoms for the formation of the nanorods and serve as a growth site as well. In the center and transition regions, ZrO2 nanorods with a diameter of 30–54nm finally grow into a network of ZrO2 layer during the cooling process. In the border region, due to the appropriate growth temperature and adequate ZrO2 vapors, ZrO2 nanorods with a significant increase in length are synthesized during the ablation process. [Copyright &y& Elsevier]

Abstract: In order to improve the ablation resistance of carbon/carbon (C/C) composites, a ZrC nanostructured coating was prepared on C/C composites by chemical vapor deposition. Results show that the coating contains ZrC grains with the size of 20–30nm and the structure displays a high consistent orientation. This nanostructured coating has improvements in linear and mass ablation rates of 50.7% and 42.1% compared with those of the conventional ZrC coating. The good ablation resistance could be attributed to the efficient prevention of the coating cracking and the formation of the dense ZrO2 layer during ablation. [Copyright &y& Elsevier]

To increase the oxidation resistance of carbon/carbon (C/C) composites at high temperature, it was modified by ZrB 2 –SiC ceramics with precursor infiltration and pyrolysis process, then SiC coating was prepared on the modified composites by pack cementation. The results show that the SiC coating prepared with Si/C weight ratio of 6:0.5 has better oxidation resistance, It can effectively protect C/C composites for 100 h at 1773 K with the weight gain per unit area of 7.75 g cm −2 . The good oxidation resistance of the coated composites is attributed to the formation of dense SiO 2 glass during the oxidation test. [ABSTRACT FROM AUTHOR]

Abstract: A C/SiC oxidation resistance coating was prepared on carbon/carbon (C/C) composites by slurry and pack cementation. The microstructure, oxidation resistance and mechanical properties of C/SiC coating prepared from 1773 to 2573K were investigated. With the increase of the preparation temperature, the oxidation resistance of C/SiC coating increases, however, the flexure strength decreases gradually. The preparation of C/SiC coating on C/C composites results in the fracture behavior of C/C composites changing from pseudo-plastic to brittle failure model. The decrease of flexure strength is mainly attributed to the decrease of C/C matrix’ flexure strength at high temperature. [Copyright &y& Elsevier]

Abstract: A hot-pressing reactive sintering (HPRS) technique was explored to prepare SiC coating for protecting carbon/carbon (C/C) composites against oxidation. The microstructures of the coatings were analyzed by X-ray diffraction and scanning electron microscopy. The results show that, SiC coating obtained by HPRS has a dense and crack-free structure, and the coated C/C lost mass by only 1.84wt.% after thermal cycles between 1773K and room temperature for 15 times. The flexural strength of the HPRS-SiC coated C/C is up to 140MPa, higher than those of the bare C/C and the C/C with a SiC coating by pressure-less reactive sintering. The fracture mode of the C/C composites changes from a pseudo-plastic behavior to a brittle one after being coated with a HPRS-SiC coating. [Copyright &y& Elsevier]