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Porous alumina ceramic was prepared with a combined technique of three–dimensional printing and sintering. The optimal sintering temperature for porous alumina ceramic is in the range of 1300–1400 °C. The CaSO 4 –dextrin content of green body has a decisive effect on the phase composition and flexural strength but a little effect on the porosity and Vickers hardness of porous alumina ceramic. The alumina ceramic prepared from the green body with CaSO 4 –dextrin content in the range of 12–16 wt% possesses a flexural strength higher than 80 MPa, a porosity of about 50% and a tailored microstructure, which is a promising material for engineering applications. [ABSTRACT FROM AUTHOR]

A Si 3 N 4 ceramic with gradient distribution of tri–iron tetroxide (Gradient–Si 3 N 4 –Fe 3 O 4 ) was fabricated with a combined technique of chemical precipitation and directional infiltration. Electromagnetic wave could enter Gradient–Si 3 N 4 –Fe 3 O 4 with little reflection because of weak impedance mismatch at its surface. Also the electromagnetic wave entering the Gradient–Si 3 N 4 –Fe 3 O 4 propagated with small reflection due to continuous and gradual change of impedance resulting from the gradient Fe 3 O 4 distribution, and was absorbed completely by Fe 3 O 4 of the gradient structure. [ABSTRACT FROM AUTHOR]

The analysis of failure behaviors of continuous fiber-reinforced ceramic matrix composites (CMCs) requires the characterization of the damage evolution process. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso architecture, inherent defects, and loading conditions. In this paper, the in-plane tensile mechanical behavior of a plain woven SiC f /SiC CMC was investigated, and damage evolution and failure process were studied in detail by digital image correlation (DIC) and acoustic emission (AE) methods. The results show that: the initiation of macro-matrix cracks have obvious local characteristic, and the propagation paths are periodically distributed on the material surface; different damage modes (matrix cracking and fiber fracture) would affect the AE energy signal and can be observed in real-time; the significant increase of AE accumulated energy indicates that serious damage occurs inside the material, and the macroscopic mechanical behavior exhibits nonlinear characteristic, which corresponds to the proportional limit stress (PLS) of the material. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation behavior and oxidation mechanism of carbon materials containing silicon and boron elements (C–Si–B materials) were investigated at different high temperatures in air. The carbon materials were prepared by oxidative pyrolysis of the polymer precursor, carborane-incorporated poly(dimethylsilylene-ethynylenephenyleneethynylene) (CB-PSEPE), at 800, 1000, or 1200°C for 1h under static air. Homogeneous dispersion of silicon and boron components in the carbon matrix could be achieved in the carbon materials after the pyrolysis. The oxidation behavior of the C–Si–B materials during the oxidation process was studied. The evolution of elemental composition and morphology of the surface layers of carbon materials was monitored by X-ray photoelectron spectroscopy and scanning electron microscopy, respectively. The results imply that the formation of protective borosilicate layer in the surface is the main mechanism to provide remarkable oxidation resistance of the carbon materials. The obtained borosilicate layer with a self-healing property can withstand oxidation at 1000°C in air. [Copyright &y& Elsevier]

Abstract: Three dimensional (3D), seven-directional braided (SiO2)f/SiO2 composites were prepared by silica sol-infiltration-sintering (SIS) method. The flexural properties were evaluated by three-point bending test. The flexural strength and flexural elastic modulus were found to be about 107MPa and 17.5GPa, respectively. The results of stress vs. deflection curve and SEM examination revealed that the fracture mechanism of the (SiO2)f/SiO2 composite was a mixed mode of brittle and ductile. The bond strength of fiber/matrix was weak at low temperature, causing the extensive fiber pull-out. On the other hand, the brittle fracture of some fibers maybe caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process. [Copyright &y& Elsevier]

A recently developed gel casting system based on water soluble epoxy resin was successfully applied to sialon ceramics. The solids loading could reach 48.9% without any pH adjustment, and all slurries exhibited shear-thinning behaviour. Flexural strengths of sialon ceramic obtained from 44.5 vol% slurry were 295.2 MPa at room temperature and 281.4 MPa at 700 °C; the microhardness was 16.5 GPa. The net-shape manufacturing of sialon ceramics could benefit from this investigation. [ABSTRACT FROM AUTHOR]

Abstract: The effect of two different fiber architectures on the mechanical properties and mechanical behavior of the SiO2f/SiO2 composites processed by silicasol-infiltration-sintering has been investigated. The composites were sintered at relatively low temperature (450°C). The fiber/matrix interface strength was weak. The characteristics of 2.5D (shallow straight-joint) structure and 3D four-directional braided structure were determined. The tensile strength, flexural strength, shear strength and failure mechanisms of both 2.5D (shallow straight-joint) and 3D four-directional braided SiO2f/SiO2 composites were characterized. It was found that the fiber placement in the preform will strongly affect the mechanical property and failure behavior of the composite. The results of the tests and microstructural observations indicated that 3D four-directional braided SiO2f/SiO2 composite had better mechanical properties than 2.5D (shallow straight-joint) SiO2f/SiO2 composite. 3D four-directional braided SiO2f/SiO2 composite exhibited more graceful failure under loading than 2.5D (shallow straight-joint) SiO2f/SiO2 composite. [Copyright &y& Elsevier]

Abstract: 2.5D (shallow straight-joint) quartz fibers-reinforced silica composites were successfully prepared by silicasol-infiltration-sintering method. The composites were sintered at 450°C and the density of the composite was up to 1.70g/cm3 after 11 infiltration-sintering cycles. The characteristics of 2.5D (shallow straight-joint) structure were determined. Flexural strength and shear strength of the composites were investigated along the warp and weft directions. The undulation of warp yarns could reduce the mechanical properties of the composites along warp direction. The flexural and shear stress-deflection curves exhibited mostly nonlinear behavior. The failure was not catastrophic. Some fibers pull-out indicated that the composite exhibited a certain degree of toughness. Microstructural observations revealed that the interface strength between the fiber and the matrix was weak for the relatively low sintering temperature of 450°C. [Copyright &y& Elsevier]