The growth and characteristics of CVD SiCTiC in-situ composites

Abstract

SiCTiC in-situ composites have been synthesized by low pressure chemical vapour deposition on graphite with SiCl 4, TiCl 4 C 3H 8 and H 2 reaction gases to improve the toughness of SiCTiC ceramics. The composite was deposited at various temperatures (1500~1600 °C), total pressure (40~300 torr) and reactant concentrations. The microstructure was investigated by scanning electron microscopy, optical microscopy and transmission electron microscopy. The morphologies of facet structure, nodular structure and dendrite structure appear depending on the experimental conditions. A dense SiCTiC deposit without porosity was obtained with a maximum growth rate of 1.6mm h −1 at C 3H 8 = 25 cm 3 min −1 and 200 torr. Only β-SiC and TiC phases have been identified in the composite with a dramatic change of the composition at the interface of SiC and TiC grains. The fracture toughness (K Ic) determined by the indentation method exhibits a value as high as 5.9 MPa m 1 2 that could be obtained by deposition at low pressure and low C 3H 8 concentration. Cracks propagate with more deflection in the SiCTiC composites than in monolithic SiC. The result is due to existing severe strain at the SiCTiC interface observed by transmission electron microscopy.