PhD Studentship: Processing of Ceramic Matrix Composites via Polymer Impregnation and Pyrolysis

Funder: The funding comes from Dstl, the Defence Science & Technology Laboratory, via the Defence Materials Centre of Excellence (DMEx), hosted by the Royce Centre at the University of Manchester. The PhD funding will last for 3.5 years.

For the modern material scientist and engineer, advanced technical ceramics provide an invaluable solution to the design of materials for use in extremely challenging, high- and ultra-high temperature environments. However, in order to successfully exploit ceramics for service under these conditions, it is necessary to fabricate thermostructural components from fibre-based ceramic matrix composites (FRCMCs). The latter, particularly continuous fibre-reinforced CMCs, are engineered to overcome the inherent brittleness of monolithic (single phase) ceramics by providing superior strength and toughness.

Nevertheless, there are still many challenges, particularly the high cost of these materials and their manufacture. This currently restricts FRCMCs to a limited number of critical components in applications where material performance is paramount. To addresses these challenges, low-cost manufacturing routes are required, one of which is via the pyrolysis of polymeric precursors. Ceramics obtained by this technique are typically referred to as polymer-derived ceramics (PDCs) and, although their origins can be traced back to the 1970s, recently they have become the subject of a great deal of both academic and commercial interest.

Over the last fifty years, great strides have been achieved in the science of PDCs with significant progress being made towards improving their processability and subsequent shaping, understanding the resulting nano / microstructure structure and enhancing their functional properties with fillers. The development of new preceramic polymers has also been a major success, in particular the poly(silazanes), which yield SiCN-based ceramics that offer much potential for use as high-temperature, structural ceramics.

In addition, the modification of PDCs with specific atoms and groups can be used to tailor the ceramic microstructures to make them more appropriate for specific high-temperature applications. For example, aluminium-modified SiCN is a promising ceramic that has been shown to enhance the long-term oxidation resistance up to temperatures of 1400°C in both wet and dry environments for hundreds of hours. It achieves this by forming a unique aluminium-doped oxide layer that can better inhibit oxygen and water ingression during oxidation and hence, in the context of high-temperature FRCMCs, it can reduce or even avoid the need to use environmental barrier coatings (EBCs) to protect the FRCMC during use; EBCs being both complex and expensive to make.

However, at high temperatures the matrix can change from being amorphous to crystalline. This phase change is associated with significant shrinkage and cracking limiting operational use. The inclusion of a specific other element into the ceramic matrix is proposed to increase the temperature at which this phase change will occur allowing use at higher operating temperatures. This 3.5-year funded PhD studentship, to start Oct 2025, will explore this phenomenon.

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