The Oxidation of SiC Fiber and SiC Fiber Reinforced Boron Phenolic Resin Composite

The SiC fiber was thermally treated in air atmosphere and the SiC fiber reinforced boron phenolic resin composite was prepared by hot molding process by introducing inorganic ceramic particles. The thermal stabilities, the surface microstructures, the diameter and oxygen mental content variations, and the crystal structures of SiC fiber heated and kept for 0.5 h and 1h at different high temperatures were investigated through TG, SEM, XRD analysis. The cross-section morphology of the composite also observed. The results showed that the SiC fiber had good thermal resistance at high temperature in N2, however it was easy to be oxidized at high temperature in air. When heated from 25 °C to 1600 °C and kept for 1 h, the fiber was oxidized to SiO2 and the fiber surface was coarse and cracked. With the temperature increasing, the diameter of the fiber decreased and the oxygen content increased. Highly different form the cross-section morphology of SiC fiber itself heated in air, the cross-section morphology of SiC fiber in composite was weakly oxidized and the cross section was smooth and there was no distinct oxidation layer existing.

Effects of interfacial residual stress on mechanical behavior of SiCf/SiC composites

Layer-structured interphase, existing between reinforcing fiber and ceramics matrix, is an indispensable constituent for fiber-reinforced ceramic composites due to its determinant role in the mechanical behavior of the composites. However, the interphase may suffer high residual stress because of the mismatch of thermal expansion coefficients in the constituents, and this can exert significant influence on the mechanical behavior of the composites. Here, the residual stress in the boron nitride (BN) interphase of continuous SiC fiber-reinforced SiC composites was measured using a micro-Raman spectrometer. The effects of the residual stress on the mechanical behavior of the composites were investigated by correlating the residual stress with the mechanical properties of the composites. The results indicate that the residual stress increases from 26.5 to 82.6 MPa in tension as the fabrication temperature of the composites rises from 1500 to 1650 °C. Moreover, the increasing tensile residual stress leads to significant variation of tensile strain, tensile strength, and fiber/matrix debonding mode of the composites. The sublayer slipping of the interphase caused by the residual stress should be responsible for the transformation of the mechanical behavior. This work can offer important guidance for residual stress adjustment in fiber-reinforced ceramic composites.

All-SiC Fiber-Optic Sensor Based on Direct Wafer Bonding for High Temperature Pressure Sensing

This paper presents an all-SiC fiber-optic Fabry-Perot (FP) pressure sensor based on the hydrophilic direct bonding technology for the applications in the harsh environment. The operating principle, fabrication, interface characteristics, and pressure response test of the proposed all-SiC pressure sensor are discussed. The FP cavity is formed by hermetically direct bonding of two-layer SiC wafers, including a thinned SiC diaphragm and a SiC wafer with an etched cavity. White light interference is used for the detection and demodulation of the sensor pressure signals. Experimental results demonstrate the sensing capabilities for the pressure range up to 800 kPa. The all-SiC structure without any intermediate layer can avoid the sensor failure caused by the thermal expansion coefficient mismatch and therefore has a great potential for pressure measurement in high temperature environments.