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Graphene nanoplatelets (GNPs) were used as reinforcement in the TiCuZrNi brazing alloy for joining carbon/carbon composites (C/C) to Ti6Al4V. The microstructure and fracture behavior of bonded joints were investigated. The results showed that the shear strength of C/C-Ti6Al4V joints with GNPs was much higher than that of the joints without GNPS. The improvement of shear strength was mainly caused by the fact that the existence of TiC particles and GNPS in braze, which could reduce the CTE of brazing alloy and alleviate the residual stresses at the interface of C/C and braze. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) were used as reinforcements in the TiCuZrNi brazing alloy for joining C/C composites to Ti6Al4V. The effects of CNTs content on the shear strength and microstructure of brazed joints were investigated. The CNTs react with Ti element from the brazing alloy, forming TiC particles in situ during the brazing process. The apparent shear strength of the joints is 38 ± 2 MPa using 1 wt.% CNTs in TiCuZrNi brazing alloy, which is 73% higher than that of the joints without CNTs. An improvement of the mechanical properties was ascribed to the in situ formation of TiC particles which induced the reinforced effects such as crack deflection, interface debonding and particle fracture. When the CNTs content in the brazing alloy increased to 3 wt.%, the joints strength dramatically decreased. This is the result of the insufficient reaction between the C/C composites and the braze. Moreover, the high content of CNTs make negative effects on the wettability and penetrability of the brazing alloy. [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 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]

Carbon/carbon (C/C) composites with two different matrixes of pitch carbon and pyrolytic carbon were fabricated using 2-dimensional (2D) carbon felts preform. In order to study the effects of matrixes on mechanical properties, C/C composites with single matrix of pitch carbon were prepared. The mechanical properties were tested on CMT5304-30KN universal testing machine. Polarization microscope and scanning electron microscope were used to investigate the microstructures and fracture surface of C/C composites. It was resulted that the flexural strength of C/C composites with two matrixes was improved by 96% compared with that of C/C composites with single matrix. Meanwhile, better toughness was also obtained with two matrixes. For the composites, multilayer microstructures were generated after filling up of voids caused during carbonization of mesophase pitch by pyrolytic carbon. The multilayer microstructures were beneficial to the improvement of mechanical properties of C/C composites, especially the toughness. More energy could be dissipated during mechanical tests while cracks might extend along multiple paths, such as the interface between fiber and matrix or the interface between different matrixes. [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: MoSi2-based oxidation protective coatings for SiC-coated carbon/carbon composites were prepared using a supersonic plasma spraying at the power of 40kW, 45kW, 50kW and 55kW, respectively. Effect of spraying power on the microstructure and bonding strength of MoSi2-based coatings was studied. The results show that coatings become more and more compact and the bonding strength increases when the spraying power increases from 40kW to 50kW. At the power of 50kW, the coatings were dense and the bonding strength reached a maximum value of 14.5MPa. As the spraying power is of sufficient magnitude, many cracks and pores reappaer in coatings and the bonding strength between coating and substrate also decreases. [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]

A SiC coating for carbon/carbon (C/C) composites was produced by pack cementation to use as a bonding and buffer layer between C/C composites and bioactive ceramic for application in orthopaedic implants. The microstructure and MG63 osteoblast-like cell responses of the coating were investigated. The results confirmed that the SiC coating displayed a dense and uniform microstructure. MG63 cells attached and spread favorably on SiC coating, and cell proliferation was better on SiC coating than on uncoated C/C composites surface. The SiC coated C/C composites have the potential to be used in artificial implants. [ABSTRACT FROM AUTHOR]

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]

SiC coating for carbon/carbon composites was prepared by pack cementation method. The effects of coating process on the microstructure and the mechanical properties of C/C composites were analyzed by SEM and three-point bending test, respectively. As the infiltrated Si improved the interfaces bonding during the coating process, the flexural strength and flexural modulus of SiC-coated carbon/carbon composites were both increased by about 10% than the naked C/C composites. In addition, the mechanism of the change of failure mode of SiC coated C/C composites and naked C/C composites was addressed. [ABSTRACT FROM AUTHOR]

C/C composites reinforced using carbon felt and 3 K carbon cloth laminated preforms were prepared by chemical vapor infiltration and samples taken from them were subsequently subjected to heat treatment at 2500 °C. The microstructures of the C/C composites were characterized by X-ray diffraction, polarized light microscopy and Raman spectroscopy. Results showed that the matrix of composites reinforced with carbon felt contained only high textured (HT) pyrolytic carbon, while those reinforced with the 3 K carbon cloth had a banded texture composed of isotropic, HT and medium textured (MT) pyrolytic carbon when moving from fibers to matrix, and the content of HT pyrolytic carbon was less than 50%. Regardless of the preform, both the as-prepared and heat-treated composites had a similar degree of graphitization. The L c value of the carbon felt-reinforced composites was higher than their counterparts both for the as-prepared and heat-treated samples. The L a values of the carbon fibers, MT and HT pyrolytic carbon increased after the heat treatment, and the L a value of the HT pyrolytic carbon had a much larger increase than that of the others. [New Carbon Materials 2014, 29(5): 369–373] [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: To protect carbon/carbon (C/C) composites against oxidation, a MoSi2 outer coating was prepared on pack-cementation SiC coated C/C composites by a hydrothermal electrophoretic deposition. The phase composition, microstructure and oxidation resistance of the prepared MoSi2/SiC coatings were investigated. Results show that hydrothermal electrophoretic deposition is an effective route to achieve crack-free MoSi2 outer coatings. The MoSi2/SiC coating can protect C/C composites from oxidation at 1773K for 346h with a weight loss of 2.49mgcm−2 and at 1903K for 88h with a weight loss of 5.68mgcm−2. [Copyright &y& Elsevier]

A SiC coating for carbon/carbon(C/C) composites was produced by a pack cementation technique in an argon atmosphere. The phase, microstructure and anti-oxidation property of the SiC coatings prepared from 1773 to 2273 K were investigated. It is found that the porous β-SiC coatings occur at 1773–1973 K while dense Si/β-SiC coatings generate at 2073 K and micro-cracked β-SiC/α-SiC coatings appear at 2173–2273 K. The thickness of the SiC coating increased with increasing temperature and oxidation tests at 1773 K in air showed that, based on observed weight changes, a preparation temperature of 2073–2273 K gave much improved oxidation resistance over that of coatings formed between 1773 and 1973 K. [Copyright &y& Elsevier]

Abstract: A new kind of composites – graphite grain/carbon (G/C) composites prepared by thermal gradient chemical vapor infiltration technology and elementary properties are investigated, and the microstructure evaluated. It is observed that pores among graphite grains are filled with pyrocarbon effectively, therefore, G/C composites with high density can be obtained. These composites offer the high temperature properties of carbon material, and excellent mechanical properties and isotropy. [Copyright &y& Elsevier]

Highlights • Cyclic thermal loading was performed on C/C-(Zr-Si-B-C-O) composites between −120 °C and 120 °C for up to 200 cycles. • Extreme-temperature thermal cycling (ETC) resulted in a 16.98% flexural strength decrease after 200 cycles. • Microcracks and interfacial debonding lead to the increase of the open porosity with ETC increasing. • Cyclic exposure to high-temperature oxidation has been carried out to test self-sealing behavior. • Exceeding 50 ETC cycles, the Zr-Si-B-C-O matrix could not heal the rapidly generated defects during HT oxidation tests. Abstract Microstructures, mechanical properties, and oxidation resistance of ZrC-SiC-ZrB 2 -ZrO 2 modified carbon/carbon composites (C/C-(Zr-Si-B-C-O)) have been investigated in the simulated space environment with different extreme-temperature thermal cycling (ETC) treatment. Cyclic thermal loading was performed in the temperature range between −120 °C and 120 °C for up to 200 cycles. Results showed that the microstructure degradation of the composite after ETC treatment was attributed to the formation of microcracks and the interfacial debonding. ETC treatment resulted in a 16.98% flexural strength decrease after 200 cycles. An oxidation model on the microstructure evolution of ETC treated C/C-(Zr-Si-B-C-O) composites was proposed to explain the oxidation failure mechanism. [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: Straight carbon nanotubes (CNTs) were grafted radially onto carbon fibers and they were used to enhance mechanical strength retention rate (i.e. the percentage of mechanical strength after graphitization as that before graphitization) of laminated carbon/carbon (C/C) composites after graphitization. Results show that out-of-plane compression strength and interlaminar shear strength retention rates of C/C composites increase from 34.7% and 42.1% to 76.2% and 84.9% after adding CNTs, showing 120% and 102% improvements. Analyses demonstrate that these great improvements are the result of simultaneous reinforcements to the fiber/matrix (F/M) interface and the matrix provided by the radially grafted CNTs, which can effectively inhibit the microstructure defects such as F/M interface debonding and matrix annular cracking occurred around carbon fiber during graphitization and then greatly increase the mechanical strength of graphitized C/C composites. [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]