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Abstract: In order to increase the oxidation resistance of carbon/carbon (C/C) composites at long‐term high temperature, C/C‐Ultra High Temperature Ceramics composites (UHTCs) with a dual‐layer UHTCs oxidation coating was successfully designed and fabricated. The microstructure and ablation resistance were investigated and discussed. After ablation in arc‐heated wind tunnel with temperature being 2200°C for 1000s, the mass ablation rate and linear ablation rate were −1.9 × 10−2 mg/cm2s and 2.9 × 10−5 mm/s, respectively. The formation of thermodynamically compatible oxide scale including ZrO2 skeleton and SiO2 or Zr–Si–O glass on the surface were mainly contributed to the excellent ablation resistance of the composite. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced carbon matrix composites (C/Cs), as important candidate aviation and aerospace materials, have good prospects for application in extreme environments. However, notch effects of C/Cs have not been studied adequately. In this work, the notch effects of 3D-C/C composites were investigated by the full-field measurement digital image correlation method. Six kinds of specimens with different notch patterns including one central hole, multi-holes, and double edge notches, were examined to analyze their mechanical properties. The tests were carried out on MTS 809 testing machine and the deformations of specimens were monitored by a CCD camera. Using the full-field measurement, both the local mechanical properties (stress concentration, shear damage, and fracture behavior) and the globe properties (notch sensitivity and tensile behavior) were studied. The results indicated that the fracture stress on the net cross section was constant and it was independent on the material heterogeneity, notch patterns, and notch depth. [ABSTRACT FROM AUTHOR]

In order to improve the oxidation behavior of carbon/carbon composites in a wide range of temperature, a new SiC/glaze-precursor coating was developed.The SiC layer was produced by slurry and sintering, while the glaze precursor layer was prepared by slurry and drying. The microstructures and phase compositions of the coating were analyzed by SEM and XRD, respectively. The oxidation resistance of the coated composites was investigated using both isothermal and temperature-programmed thermogravimetric analysis in the temperature range from room temperature to 1600 °C. The results showed that the oxidation behavior of the coating was mainly controlled by the diffusion of oxygen during the test.The coating showed excellent oxidation resistance and self-healing ability in a wide range of temperature. [ABSTRACT FROM AUTHOR]

Carbon/carbon composites usually work in complex thermo-chemical environments, surface recession is thus inevitable due to chemical ablation and further affects the system stability and safety. In this paper, a model for chemical ablation of the materials which accounts for the effects of non-uniform temperature and pressure is proposed. As an application, the surface recession of a carbon/carbon composites leading edge structure are simulated in detail. The results show that the non-uniform distributed pressure plays an important role in the final ablation configuration. The effects of altitude and oxidation protection on the chemical ablation are discussed as well. [ABSTRACT FROM AUTHOR]

Abstract: B4C/graphite composites (BGC) containing substitutional boron were fabricated by pressureless sintering of powder mixtures of petroleum coke, coal tar pitch and B4C. After sintering at 900°C and graphitizing at 2200°C, the microstructure of BGC was characterized by SEM, TEM, XRD, Raman spectroscopy and optical microscopy. XPS measurements revealed the formation of BC3, and the matrix carbon contained around 6wt.% substitutional boron. The thermal conductivity of the BGC at room temperature is 52.7W/mK and the flexural strength is up to 35.1MPa. The bulk density and electrical resistivity are 1.72g/cm3 and 13.4μΩm, respectively. The correlation between microstructure and properties was investigated. The results showed that the microstructure improvement of the BGC has obvious effect on the thermal conductivity, flexural strength, and electrical resistivity. [Copyright &y& Elsevier]