Lidong Zhang

Fibre-reinforced multifunctional SiC matrix composite materials

In the last two decades, fibre-reinforced SiC ceramic-matrix composites (CMCs) have attracted extensive interests. Owing to the designable multi-scale microstructure feature and the tailorable processing methods such as chemical vapour infiltration and polymer derived ceramics, SiC matrix composites attain great potential as multifunctional composites. Through designing the fibre, interphase, matrix and coating, the composite exhibits a multitude of functionalities which are desirable for various technological applications. Besides strengthening and toughening design of CMCs, three inspiring issues of multifunctional CMCs are receiving increasing attention, including crack self-healing, friction self-lubrication, and electromagnetic shielding and absorption, which are the key mechanisms to promote the application of CMCs in hot structures of engines and aerospace vehicles, braking pads/discs, various electronic devices, etc. The present review covers the main mechanisms on strengthening and toughening, crack self-healing, friction self-lubrication, and electromagnetic shielding and absorption of CMCs. Key developments and future challenges in this field are summarised.

Oxidation behaviour of three-dimensional woven C/SiC composites

Abstract The oxidation behaviour of a three-dimensional woven C/SiC composite protected with an SiC seal coating and with an SiC coating combined with an SiO2–B2O3 glassy coating have been respectively investigated through an experimental approach based on mass and flexural strength changes. Three main temperature domains exist for C/SiC composites protected with an SiC seal coating. At low temperatures (<700°C), the mechanisms of reaction between carbon and oxygen control the oxidation kinetics. At an intermediate temperatures (between 700 and 1100°C), the oxidation kinetics are controlled by gas phase diffusion through a network of microcracks in the SiC matrix and coating. At high temperatures (>1100°C), the oxidation kinetics are controlled by oxygen diffusion through the SiO2 scale formed on the SiC coating. Composites of C/SiC with an SiC/(SiO2–B2O3) coating exhibit better oxidation resistance. The filling of the pores and the microcracks and the flow of the glassy coating at higher temperatures result in a global decrease of mass loss in the composites. By researching the relationship between the residual flexural strength and the mass variation in different temperature ranges, it is shown that the change in the residual flexural strength is dominated by the degradation of carbon phase.

Continuous synchronous composite process for fabricating carbon/silicon carbide composites

The continuous synchronous composite (CSC) process is a new technique, the preparation of reinforcement-phase accompanied simultaneously the deposition of SiC matrix, based on CVI principles for fabrication of ceramic matrix composites. In the CSC process, there was a gradient temperature field on the surface of the graphitic substrate, consisting of high (1000–1200°C), intermediate (900–1000°C) and low (700–900°C) temperature regions, by a bottom heating-element. Following the rotating substrate, micro-pores were well infiltrated in the intermediate temperature regions by gas diffusion transport, and macro-pores were rapidly filled with SiC in the high temperature regions by gas flow transport, respectively. In the present paper, 2-dimension carbon cloth reinforced SiC composites was fabricated by CSC process, and the microstructure, deposition rate and conversion efficiency of methyltrichlorosilane (MTS) were investigated. The densification of C/SiC composites was uniform, and the highest deposition rate within macro-pores was 25 μm h−1, and the conversion efficiency of MTS varied from 11% to a maximum of 27%.

Matrix modification of laminated SiCw/SiC ceramic composites

Laminated SiCw/SiC ceramic composites were fabricated by chemical vapor infiltration and tape casting, and the effects of matrix modification on microstructure and strengthening/toughening of the composites were investigated by polymer infltration and pyrolysis and liquid silicon infiltration. With increasing cycles of polymer infltration and pyrolysis, density of the composites increased effectively, and the flexural strength and fracture toughness increased obviously. With increasing time of liquid silicon infiltration, density of the composites increased significantly, but the flexural strength and fracture toughness increased firstly and then decreased gradually. After modification by polymer infiltration and pyrolysis, the bonding of interfacial and interlaminar was not changed, and the density increase led to the property increase. After modification by liquid silicon infiltration, the interlaminar bonding was not changed and interfacial bonding of whisker/matrix was strengthened, and the density increase led to the property increase.