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A study on the influence of the silicate composition on the self-healing ability of a promising environmental barrier coating (EBC) material is reported. The EBC material consists of silicon carbide particles dispersed in a ytterbium silicate matrix. The composition of the silicate was varied from pure monosilicate to pure disilicate including a mixture of 50 vol-% of both phases. Pre-cracked specimens were mechanically tested before and after thermal annealing in air at 1400 °C accompanied by microstructural investigations. It is shown, that the self-healing mechanism is based on the application of compressive surface stresses due to graded oxidation of the SiC particles. With increasing amount of disilicate strength and self-healing ability increase. [ABSTRACT FROM AUTHOR]

Superhard silicon carbide-bonded diamond materials were synthesized by liquid silicon infiltration of diamond-containing preforms. The properties of the materials were strongly influenced by the strength of the interfaces between the diamond and the silicon carbide. Interface formation was investigated through local analysis of the microstructure in the interface regions using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) as well as X-ray diffraction (XRD). The results of these experiments revealed a pronounced orientation relationship between SiC and diamond at their interfaces and, as a result, strong bonding of the diamond particles to the ceramic matrix. There was also an orientation relationship between the nano-sized SiC grains, which were embedded in residual silicon near the diamond interfaces, and diamond. Additionally, the different morphologies and phenomena occurring in the microstructures of the diamond-SiC composites and their dependence on the infiltration temperature were studied. [ABSTRACT FROM AUTHOR]

Abstract: SiC-fiber/SiCN ceramic matrix composites were manufactured by means of polymer infiltration and pyrolysis. The fiber preform was made by slurry infiltration and winding using a computer-controlled winding module. Multiple infiltration steps using a Si–C–N precursor were included to increase the density. The influence of the sintering conditions on the microstructure of the CMC was demonstrated. Pipe sections made of the CMC materials were joined using a laser-supported heating technology with an Y–Al–Si–O glass–ceramic filler. The thermal response of the CMC components was controlled by the anisotropic thermal conductivity. Fast heating by laser beam was achieved for elements rotating in the direction of the fiber winding. SEM micrographs of the joints showed the good wettability of the CMC by the glass–ceramic filler. Nearly defect-free joints were obtained using a nitrogen process atmosphere. The laser-supported technology was shown to be promising for the joining of CMC components. [Copyright &y& Elsevier]

Abstract: Sintered silicon carbide materials have found widespread use due to their high corrosion stability. This corrosion stability can be affected by electrochemical processes. Electrochemical corrosion experiments conducted on a SSiC material in H2SO4 at different voltages and subsequent detailed investigation of the formed surfaces was carried out. The first time a systematic local measurement of the thickness of the oxide layers was carried out. The measurements revealed the formation of SiO2 surface layers with thickness up to 125μm. The measured values also showed a strong deviation from grain to grain. The thickness of the layers does not correlate with the crystallographic orientation of the grains or the SiC-polytypes. The data indicate that the behaviour is caused by the variation of the resistivity of the grain boundaries. The measured thicknesses as a function of the electrical charge transferred indicate that the electrochemical oxidation results in the SiO2 and carbon dioxide. [Copyright &y& Elsevier]

Abstract: Materials with enhanced wear resistance are of great interest for modern industry. The different ways of producing superhard ceramic materials are shortly reviewed. In detail, the preparation of diamond–silicon carbide composites by reactive infiltration of diamond preforms with liquid silicon at ambient pressure is investigated. In addition to homogeneous SiC/diamond materials with nearly 50vol.% of diamond layered composites were also prepared. The microstructures of the materials prepared under different infiltration conditions were analyzed using X-ray diffraction, electron microscopy, electron back-scatter diffraction (EBSD) and Raman spectroscopy. The properties of the materials depend strongly on the formation of graphite interlayers at the boundary between SiC and diamond. Hardness of 47GPa was reached for materials where the formation of the interlayer was prevented. [Copyright &y& Elsevier]

Abstract: New electrically conductive ternary composites were developed by adding 8vol.% of ZrN or ZrB2 to a Si3N4–SiC matrix. During hot pressing, ZrB2 reacted with Si3N4 to form ZrSi2, ZrN, Si and BN whereas added ZrN did not undergo any reactions in the Si3N4–SiC–ZrN composite. The composites modified by ZrN or ZrB2 addition showed a lower resistivity (7×103 Ωcm and 3×10−1 Ωcm) compared to the matrix (3×104 Ωcm). Further studies on the grain size distribution and the volume ratio of conducting and non-conducting phases excluded a percolation network of ZrN and ZrSi2 grains. In fact, doping of SiC grains and modified grain boundaries as a consequence of the formation of liquid phases during sintering are suggested to be the reason for the significantly lower resistivity of materials containing ZrSi2. A decrease in the composite resistivity due to a subsequent heat treatment was obtained for all hot-pressed composites. [Copyright &y& Elsevier]