Microstructural characterisation of advanced ceramics and their composites

Advanced ceramics are used in a wide variety of engineering applications, including use in transportation (aerospace, automotive, marine), chemical processing, waste incineration, pulp and paper processing, electronics and computing, etc. The development of new ceramics, and their composites, requires a detailed knowledge of the inter-relationships between the way the material has been processed, the resulting microstructure, and the properties of the material. Silicon nitride (Si3N4), silicon carbide (SiC) and titanium carbide (TiC) are all examples of advanced engineering ceramics that are used in the industrial areas outlined above. Our group is investigating the processing-microstructure-property relationships for each of these materials, and in many cases their composites. The current RTI proposal relates to the purchase of of plasma etching system that will allow far more detailed microstructural evaluation of these materials than has previously been possible within our group. In particular, plasma etching using reactive gas mixtures (i.e. CF4/O2) has been shown to etch these ceramics, and related materials such as Si-Al-O-Ns and silicon oxynitride (Si2N2O) at slightly different rates, thus allowing clear discrimination between the phases in multi-phase composites. Similarly, the growth of grains is made visible, as the original seed grain etches at a slightly different rate, such that growth bands are clearly visible in Si3N4 ceramics that have been subjected to cyclic annealling. Much of our current work is targetted towards the development of novel, low cost processing methods for these ceramics and their composites, and consequently the plasma etching system will be invaluable for their microstructural characterisation, allowing us to perform detailed analysis that currently is impossible.