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A slurry-based laser cladding technique was used to repair the SiC coated carbon/carbon composites. The oxidation resistance of repaired samples at 1773 K for 10 h was investigated. Samples were characterized by X-ray diffraction pattern, scanning electron microscopy and confocal microscope; its interface characteristics were studied with scratch, thermal shock and internal friction tests. The results show that there is no obvious interface between the newly-formed coating and the original coating, and the newly-formed coating has a much smoother surface. With optimizing parameters, the new coating of 180 μm thickness possesses refined grains, flat surface, dense microstructure and good thermal stability. The number of internal defects in the samples repaired by laser cladding drops, compared with the damaged/undamaged samples. The weight loss of repaired samples decreases by 64.8% in comparison with the damaged ones, and it is almost the same with the undamaged samples according to a test of anti-oxidation behaviors. This is attributed to the enhanced oxidation resistance of dense newly-formed coating, which makes carbon/carbon composites well protected. [ABSTRACT FROM AUTHOR]

To protect carbon/carbon composites against oxidation and ablation, a Fe 2 O 3 modified ZrB 2 –SiC–Si coating was prepared by a two-step pack cementation. The microstructure, oxidation and ablation resistance of the Fe 2 O 3 modified ZrB 2 –SiC–Si coating were studied. The results showed that the Fe 2 O 3 modified ZrB 2 –SiC–Si coating had good oxidation and ablation resistance, and could effectively protect the carbon/carbon composites from oxidation at 1773 K for 150 h and ablation at 2573 K for 60 s. The excellent oxidation and ablation resistance of the coating were mainly attributed to its dense and large amount of ZrB 2 in the coating. [ABSTRACT FROM AUTHOR]

Abstract: A self-sealing Si–Mo–B oxidation resistance coating was prepared on C/SiC coated carbon/carbon (C/C) composites by slurry and high temperature treatment method. The oxidation resistance of the coating increases at 1173K and first increases then decreases at 1873K with the increase of B content from 0 to 20wt.%. The C/SiC/gradient Si–Mo–B multilayer coating can protect C/C composite from oxidation for 100h at 1173K and 125h at 1873K. The good oxidation resistance of the coating in broad temperature range could be attributed to its good self-sealing property. [Copyright &y& Elsevier]

To protect carbon/carbon (C/C) composites against oxidation, ZrSiO oxidation protective coating was prepared on SiC-coated C/C composites by supersonic plasma spraying. X-ray diffraction and scanning electron microscopy were used to analyze the phase and microstructure of the coating. The results show that the as-prepared ZrSiO coating is continuous and well bonded with the SiC inner layer without penetrating crack, which exhibits good oxidation-resistant properties. After oxidation at 1773 K in air for 97 h and nine thermal shock cycles between 1773 K and room temperature, the weight loss of the coated C/C composites was only 0.08%. The excellent oxidation-resistant properties of the coating were attributed to its dense structure and the formation of the stable ZrO-SiO glassy mixture on the surface of ZrSiO coating. [ABSTRACT FROM AUTHOR]

Abstract: A MoSi2–CrSi2–Si/B-modified SiC coating was prepared by two-step pack cementation. The coating could protect C/C composites from oxidation at 1173K for 600min and at 1873K for 300h and from erosion at 1873K for 50h, respectively. B2O3 oxidised from B-modified SiC layer could seal cracks at intermediate temperatures, resulting in improving the oxidation resistance of the coating. Large cracks caused by the bending of the coated specimens and excessive local stress resulted in the fracture of the tested specimens. [Copyright &y& Elsevier]

Abstract: The high-temperature erosion resistance of multi-layer MoSi2–CrSi2–Si/SiC coated carbon/carbon (C/C) composites was investigated in a wind tunnel. To study the aerodynamic oxidation mechanism and analyze the failure of the coated C/C composites, the shear force and bending moment distribution of the tested specimens in a wind tunnel were calculated. Flexural strengths and thermogravimetric analysis of the coated specimens were measured. These results show that the multi-layer MoSi2–CrSi2–Si/SiC antioxidation coating can protect the C/C composites from high-temperature erosion in a wind tunnel at 1873K for more than 86h. Due to the high viscosity of SiO2, the multi-layer coating lacked effective oxidation resistance from 900 to 1500K, resulting in extensive mechanical damage and the fracture of the tested specimens. [Copyright &y& Elsevier]

Abstract: To extend the oxidation protective temperature range of coating for carbon/carbon (C/C) composites, a SiC/ZrB2–SiC/SiC multilayer coating was prepared by a three-step method of pack cementation, slurry and chemical vapor deposition. The prepared coating is composed of three layers with about 150μm in thickness. It can protect C/C composites from oxidation for more than 300h at 1173K which is attributed to the oxidation ability of ZrB2. The coating can also effectively protect C/C composites from oxidation at 1773K for 217h which is due to the SiO2–ZrSiO4 compound glass during oxidation test. [Copyright &y& Elsevier]

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 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: To improve the oxidation resistance of carbon/carbon (C/C) composites, a C/SiC/MoSi2–Si multilayer oxidation protective coating was prepared by slurry and pack cementation. The microstructure of the as-prepared coating was characterized by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The isothermal oxidation and erosion resistance of the coating was investigated in electrical furnace and high temperature wind tunnel. The results showed that the multilayer coating could effectively protect C/C composites from oxidation in air for 300h at 1773K and 103h at 1873K, and the coated samples was fractured after erosion for 27h at 1873Kh in wind tunnel. The weight loss of the coated specimens was considered to be caused by the formation of penetration cracks in the coating. The fracture of the coated C/C composites might result from the excessive local stress in the coating. [Copyright &y& Elsevier]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation, a self-sealing multilayer oxidation resistant coating including a C/SiC gradient inner layer, a Si-Mo-B middle layer and a glass exterior layer was prepared by pack cementation and slurry method. Scanning electron microscopy and X-ray diffraction were used to analyze the microstructure and phase composition of the as-prepared coating. The isothermal and thermal shock oxidation resistance of the coating was also investigated. The results showed that the multilayer coating exhibited excellent oxidation resistance from room temperature to 1873K. It could effectively protect C/C composites for 100h at 1173K and 150h at 1873K, and endure 40 thermal cycles between 1873K and room temperature. The excellent oxidation and thermal shock resistance could be attributed to the gradient structure and the self-sealing property of the multilayer coating. [Copyright &y& Elsevier]

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: To protect carbon/carbon (C/C) composites against oxidation, MoSi2-based oxidation protective coatings for SiC-coated carbon/carbon composites were prepared on them by supersonic plasma spraying. The MoSi2-based coatings primarily consist of MoSi2, Mo5Si3 and glassy SiO2. Only a few pinholes and some microcracks are observed on the surface and no through-thickness cracks penetrate the cross-section. Weight loss of the MoSi2-based coated specimens is only 1.14% after 400h oxidation in air at 1773K and the coated C/C composites remain intact after 11 thermal cycles between 1773K and room temperature. The outstanding anti-oxidation ability is mainly attributable to the formation of SiO2-based layer on the surface of MoSi2-based coatings. [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 protect carbon/carbon (C/C) composites against oxidation, a SiC nanowire-toughened MoSi2–SiC coating was prepared on them using a two-step technique of chemical vapor deposition and pack cementation. SiC nanowires obtained by chemical vapor deposition were distributed random-orientedly on C/C substrates and MoSi2–SiC was filled in the holes of SiC nanowire layer to form a dense coating. After introduction of SiC nanowires, the size of the cracks in MoSi2–SiC coating decreased from 18±2.3 to 6±1.7μm, and the weight loss of the coated C/C samples decreased from 4.53% to 1.78% after oxidation in air at 1500°C for 110h. [Copyright &y& Elsevier]

Abstract: A MoSi2–CrSi2–Si multi-composition coating was prepared on the surface of SiC coated carbon/carbon (C/C) composites by pack cementation in argon. The crystalline structure of the multi-composition coating was measured by X-ray diffraction. The morphology and element distribution were analyzed by scanning electron microscopy and energy dispersive spectroscopy, respectively. The isothermal oxidation and erosion resistance of the multi-layer coating were investigated in electrical furnace and high temperature wind tunnel, respectively. These results indicated that the weight loss of the coated C/C composites was only 0.8% after oxidation in air at 1873K for 500h, and the sample was fractured after erosion at 1873K for 32h in wind tunnel. The weight loss of the coated C/C composites was considered due to the excessive depletion of the outer coating and the appearance of defects in the coating. The mismatch of thermal expansion coefficient between the multi-layer coating and C/C composites caused excessive local stress and resulted in the fracture of the coated C/C composites. [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: To prevent carbon/carbon (C/C) composites from oxidation, a Si–SiC coating has been prepared by a two-step pack cementation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis show that the coating obtained by the first step pack cementation is a porous β-SiC structure, and a dense structure consisting α-SiC, β-SiC and Si is obtained after heat-treatment by the second step pack cementation. By energy dispersive spectroscopy (EDS) analysis, a gradient C–SiC transition layer can be formed at the C/C-coating interface. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 166h at 1773K in air. The weigh loss of the coated C/C is due to the formation of bubble holes on the coating surface and through-coating cracks in the coating. [Copyright &y& Elsevier]

In order to protect carbon/carbon (C/C) composites from oxidation at 1700°C, a MoSi2–SiC–Si/MoSi2 coating was prepared on the surface of these composites by a simple and effective method. The MoSi2–SiC–Si inner layer was obtained by pack cementation, and the MoSi2 outer layer was prepared by slurry coating using silicon-sol as the caking agent. The microstructures of the as-prepared coating were examined by X-ray diffraction and scanning electron microscope. Oxidation test shows that, the as-received coating can protect C/C composites from oxidation for more than 107 h at 1700°C in air. The excellent anti-oxidation ability of this coating is attributed to its dense structure and the formation of the SiO2 film on the coating surface during oxidation. [ABSTRACT FROM AUTHOR]

A novel Mo–Si–B double-layer coating was prepared for the carbon/carbon (C/C) composites by pack cementation in an argon atmosphere. The structures of the double-layer coatings were characterized by XRD and SEM. The as-received coating shows an excellent oxidation resistance at high and intermediate temperature. It could effectively protect C/C composites from oxidation for 30 h with a weight loss of 0.9% in air at 1873 K, and for 25 h with a weight loss of l.7% at 1173 K. The oxidation protective coating was principally due to producing eutectic glass film for decreasing oxygen diffusing through the penetrable cracks in the coating. [ABSTRACT FROM AUTHOR]

In order to protect carbon/carbon (C/C) composites against oxidation, a (Mo,W)Si2 coating was prepared on the surface of SiC-coated C/C composites by a simple in situ information method using Si, Mo and W as starting materials. The microstructures and oxidation protective ability of the as-received coating were investigated. The results show that the (Mo,W)Si2 outer layer coating containing free Si has a good bonding with SiC inner layer. The as-prepared SiC/(Mo,W)Si2 coating can protect C/C composites from oxidation in air at 1773 K for 252 h with a weight gain of 1.56 wt.%. The excellent oxidation resistant property of the double-layer coating is attributed to its dense microstructure and the formation of the stable glassy SiO2 film on the (Mo,W)Si2 coating surface during its exposure to air at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: This work proposes a multi-composition oxidation resistant coating for SiC-coated carbon/carbon (C/C) composites by slurry method using the mixture of Y2O3, ZrO2, Al2O3, Si and C. XRD analysis shows that the phases of the composite coating are composed of SiC, Al2O3, Y2O3, ZrO2, Al4SiC4 and Y3Al2(AlO4)3. SEM analysis of the cross section of the coating displays the microstructure with 500μm thickness which filled the porous SiC. Oxidation test shows that, after 19h oxidation in air at 1873K, the weight loss of the coated SiC-C/C is only 1.76%. The oxidation of the coated C/C composites was primarily due to the reaction of C/C matrix and oxygen diffusing through the penetrable cracks and bubble holes in the coating. [Copyright &y& Elsevier]

Abstract: To protect carbon/carbon (C/C) composites from oxidation, a dense coating has been produced by a two-step pack cementation technique. XRD and SEM analysis shows that the as-obtained coating was composed of MoSi2, SiC and Si with a thickness of 80–100 μm. The MoSi2–SiC–Si coating has excellent anti-oxidation property, which can protect C/C composites from oxidation at 1773 K in air for 200 h and the corresponding weight loss is only 1.04%. The weight loss of the coated C/C composites is primarily due to the reaction of C/C substrate and oxygen diffusing through the penetration cracks in the coating. [Copyright &y& Elsevier]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation, a SiC–CrSi2 protective coating toughened with SiC whiskers (SiCw) has been prepared by a two-step technique of slurry and pack cementation. SEM and XRD analysis show that with the SiCw content increasing from 0 to 20wt.%, the coating thickness is reduced from 420 to 100μm, and the CrSi2 proportion in the coating first increases and then decreases. Oxidation tests in the range 1473–1773K shows that the coating toughened with 15wt.% SiCw possesses a better oxidation protective ability because of its more suitable thickness and microstructure. As the oxidation temperature increases from 1473 to 1773K, the oxidation protective ability of the coating improves gradually. The weight loss of the coated samples is primarily due to the reaction of C/C matrix and oxygen diffusing through the cracks in the coating. [Copyright &y& Elsevier]

Abstract: Yttrium silicate coatings with an outer glass sealant for SiC pre-coated carbon/carbon (C/C) composites were prepared by a novel in situ formation method using Si and Y2O3 as starting materials in an oxidation atmosphere. The structures of the coatings were characterized by XRD and SEM analyses. Oxidation behavior of the multi-layer-coating-coated C/C composites was investigated. It showed that the as-prepared multi-layer coating could protect C/C composites from oxidation at 1600 °C in air for 202 h with a weight loss of 2.87×10−3g/cm2. The oxidation weight losses of the coated C/C with time accorded with linear and parabolic rule in the temperature range 400–800 and 1300–1600 °C, respectively, and the corresponding oxidation activation energy of the coated C/C composites are 99.6 and 112 kJ/mol, respectively. [Copyright &y& Elsevier]

The article reports that Carbon/carbon (C/C) composites are important engineering materials for high-temperature structural applications due to their low thermal expansion coefficient, low weight, high specific strength and modulus, high creep resistance and excellent thermal shock resistance. Yttrium silicates are good oxidation resistant materials for high temperature applications because of their excellent properties such as high melting point and low oxygen infiltration. High temperature silicates such as mullite and zircon are promising candidate materials for oxidation protective coatings for C/C composites.

To improve the bonding properties of the interface between carbon/carbon (C/C) composites and a Ti-Ni-Si interlayer, an interlocking interface structure was obtained by a two-step technique involving pre-oxidation and hot-pressing. The results show that a porous layer could be obtained on the surface of C/C composites by pre-oxidation treatment at 1173 K in air and that an interlocking C/C-Ti-Ni-Si interface was formed after hot-pressing. With increasing pre-oxidation time, the average shear strength of the Ti-Ni-Si joint initially increased and then decreased. After a pre-oxidation time for 3 min, the shear strength of the joint reached a maximum of 29.81±1.76 MPa, which is 20.1% higher than the joint strength obtained without pre-oxidation. The improvement in the shear strength is primarily attributed to the ‘pinning effect’ generated by the interlocking interface, which could play a positive role in extending the crack propagation path by inducing crack deflection. [ABSTRACT FROM AUTHOR]

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]

Abstract: A C/SiC/Mo–Si–Cr multilayer coating for carbon/carbon (C/C) composites against oxidation at high temperature was prepared by pack cementation and slurry method. Oxidation test results showed that the coating could protect C/C composites from oxidation at 1873K in air for 300h and withstand 40 thermal cycles between 1873K and room temperature. The coating remained intact during the two kinds of tests and no obvious failure was found. The good oxidation and thermal shock resistance of the coating is attributed mainly to the formation of dense glass film on the coating during the oxidation test. [Copyright &y& Elsevier]

Abstract: Ablation of zirconium carbide (ZrC) modified carbon/carbon (C/C) composites was tested by an oxyacetylene torch. The formation of zirconia from the oxidation of ZrC improves the ablation resistance of the C/C composites because of the evaporation at elevated temperature, which absorbs heat from the flame and reduces the erosive attack to carbon. Zirconia also acts as an accelerator for carbon oxidation as it reacts with carbon during the ablation, increasing the mechanical breakage rate of the fibres. However, the effect of mechanical breakage is inferior in the ablation of the composites. The heterogeneous reactions control the ablation of the composites. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the oxidation resistance of carbon/carbon composites at intermediate temperatures, a novel double-layer SiC/indialite coating was prepared by a simple and low-cost method. The internal SiC transition layer was prepared by pack cementation and the external indialite glass–ceramic coating was produced by in situ crystallization of ternary MgO–Al2O3–SiO2 glass. The microstructures and morphologies of coating were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Oxidation resistance of the as-coated C/C composites was evaluated in ambient air at temperature from 800°C to 1200°C. Nearly neglectable mass loss was measured after 100h isothermal oxidation test, indicating that SiC/indialite coating possesses excellent oxidation protection ability. The as-coated samples have a good thermal shock resistance and no obvious damage was found in the coating even after suffered more than 11 thermal cycles between test temperature and room temperature. The oxidation protection mechanism of this coating was also discussed. [Copyright &y& Elsevier]

Abstract: In order to prevent carbon/carbon (C/C) composites from oxidation at 1773 K, a Si–W–Mo coating was prepared on the surface of SiC coated C/C composites by a simple pack cementation technique. The microstructures and phase composition of the as-received multi-coating were examined by SEM, XRD and EDS. It was seen that the compact multi-coating was composed of α-SiC, Si and (W x Mo1− x )Si2. Oxidation behaviour of the SiC/Si–W–Mo coated C/C composites was also studied. After 315 h oxidation in air at 1773 K and thermal cycling between 1773 K and room temperature for 17times, no weight loss of the as-coated C/C composites was measured. The excellent anti-oxidation ability of the multi-coating is attributed to its dense structure and the formation of the stable glassy SiO2 film on the coating surface during oxidation. [Copyright &y& Elsevier]

A new type of oxidation-protective multi-composition coating for carbon/carbon (C/C) composites has been produced by a pack cementation technique in an argon atmosphere. XRD analyses shows that the phases of the composite coating are composed of Al2O3, mullite, SiC and Al4SiC4, and the bonding layer between the coating and C/C composites are composed of Al4C3, SiC and Al4SiC4. It is found by SEM surface observation and EDS area scanning analyses that the coating has two kinds of surfaces that are distinctly different in element content of Si and C. In the meantime, cross-section SEM observation of the coating also displays a dense microstructure. Oxidation test shows that the as-prepared coating characterized by excellent thermal shock resistance on the surface of C/C composites during exposure to an oxidizing atmosphere at 1773 K could effectively protect the C/C composites from oxidation for 41 h. [Copyright &y& Elsevier]

In order to exploit the unique high temperature mechanical properties of carbon/carbon (C/C) composites, a new type of oxidation protective coating has been produced by a two-step pack cementation technique in an argon atmosphere. XRD analysis showed that the internal coating obtained from the first step was a gradient SiC layer that acts as a buffer layer, and the multi-layer coating formed in the second step was an Al2O3-mullite layer. It was found that the as-received coating characterized by excellent thermal shock resistance on the surface of C/C composites during exposure to an oxidizing atmosphere at 1873 K, could effectively protect the C/C composites from oxidation for 45 h. The failure of the coating is due to the formation of bubble holes on the coating surface. [Copyright &y& Elsevier]

Carbon/carbon (C/C) composites are considered the most promising materials for high-temperature structural applications owing to their excellent properties at high temperature. However, oxidation and ablation limits their applications in oxygen-containing environments at ultrahigh temperatures and high-speed gas flows. How to improve oxidation and ablation resistance of the C/C composites has become a critical issue. The methods for improving oxidation and ablation resistance of the C/C composites are reviewed, which mainly focus on optimizing the carbon fiber weave structure, controlling the pyrolytic carbon texture, modifying the matrix, and coating with anti-ablative ceramic layers. Matrix modification and coating technology have been proved to be the two effective ways of dealing with the problem. Development directions on producing oxidation and ablation resistive C/C composites are concentrated on decreasing preparation cost, controlling pyrolytic carbon texture, optimizing compositions of the doped ceramics used in the matrix and the coating layer, and combining matrix modification with an anti-ablation coating. [New Carbon Materials 2015, 30(2): 97–105] [ABSTRACT FROM AUTHOR]

To improve the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, a transition layer with mechanical interlocking structure was constructed at the interface by pre-oxidation treatment and chemical vapor deposition. For the coated specimens with pre-oxidation treatment at 1073 K for 5 min, the bonding strength increased from 2.0 to 4.0 N, and the mass loss percentage decreased by 52.5% after 12-time thermal cycling between 1773 K and room temperature in air. The transition interlocking structure can effectively alleviate the mismatch between the coefficients of thermal expansion of SiC coating and C/C–ZrC–SiC substrate, improving the bonding strength and thermal shock resistance. As the pre-oxidation time increases, a rugged and loose ZrO 2 –SiO 2 layer will be formed at the interface, which is disadvantageous to the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, and results in the debonding and collapse of the coating. [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: To prevent carbon/carbon (C/C) composites from oxidation, a dense SiC nanowire-toughened SiC–MoSi2–CrSi2 multiphase coating was prepared by the two-step technique composed of chemical vapor deposition (CVD) and pack cementation. The coatings were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). SiC nanowires could decrease the dimension of cracks and improve the oxidation and thermal shock resistance of SiC–MoSi2–CrSi2 multiphase coating. Oxidation test shows that, after introducing SiC nanowires, the weight loss of the coated sample can be reduced from 1.06% to 0.64% after oxidation at 1773K for 155h and decreased from 6.92% to 3.42% after thermal cycling between 1773K and room temperature for 30 times. [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]