Shuang Zhao

Studying SiC/SiC Composites by X-Ray Tomography

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied and developed for high temperature applications and nuclear applications. In this study, SiC/SiC composites were fabricated via polymer impregnation and pyrolysis (PIP) process and studied by X-ray tomography. The SiC/SiC composites were first scanned using a Metris X-tek 320 kV source at the Henry Moseley X-ray Imaging Facility at the University of Manchester, the closed porosities were investigated after three dimensional (3D) imaging of the samples. Furthermore, high-resolution synchrotron X-ray tomography was applied to the SiC/SiC composite at Diamond Light Source. Digital volume correlation was employed for Hertzian indentation testing of the SiC/SiC composite, quantifying damage by measurement of the displacement fields within the material. A Cellular Automata integrated with Finite Elements (CAFE) method was developed to account for the effect of microstructure on the fracture behavior of the SiC/SiC composite. Graded microstructures, textures and multiple phases were simulated and a mesh-free framework was developed to compute the damage development through the microstructure. The results indicated that we could study the development of discontinuous cracking and damage coalescence, and its sensitivity to microstructure with this method.

Oxidation Resistant Behaviour of Mullite/Yttrium Silicate Multilayer Coating for C/SiC Composites at 1500°C

Continuous carbon fibre reinforced silicon carbide (C/SiC) composites were fabricated by precursor infiltration and pyrolysis (PIP) process, a mullite/yttrium silicate multilayer coating was prepared by plasma spray method as the oxidation protective coating. The efficiency of the coating against oxidation was characterized by means of heat treatment of the C/SiC composites at 1500 °C in static air for 1 hour. The results indicated that the weight loss of the coated composites was only 3.4 %, and the flexural strength of the composites retained 95.3 % of the original strength.

Sintering Additive on the Pore Structure and Mechanical Properties of Si3N4 Ceramic Foam Produced by Protein Coagulation Casting

Silicon nitride (Si3N4) ceramic foam was prepared from water-based Si3N4 slurries via protein coagulation casting method with egg white protein as the foam agent. The open porosity of the as-fabricated ceramic foams was close to 80%, and the compressive strength was about 20 MPa. Further, the content of sintering additive on the phase composition, pore structure and pore size distribution were investigated. Results indicate that with the increasing of sintering aids, more windows appear on the wall of pore and the average size increases. Moreover, Pore size distribution of as-fabricated ceramic not only changes with sintering additive addition but also varies with pore size.