The Processing and Production of Ceramic Composites to Improve Oxidation and Strength Properties at Ultra High Temperatures

Abstract

UHTCs are at the forefront of materials research as the aerospace industry and other high tech sectors become limited in vision and scope by the shortfalls of the current generation of materials. The race is on to find a candidate material to replace C/C-SiC composites in all high temperature high strength environments. For UHTCs to improve on the current generation issues such as thermal shock, high temperature oxidation, strength and fracture toughness must be overcome. Incorporation of UHTCs into composite structures hopes to alleviate many of these issues. The thesis will be split into five key phases: procurement, synthesis, processing, testing and analysis. The synthesis phase compared the merits of silicides, oxides and diborides in the densification of UHTC composites. The research covered all refractory elements and common sintering aids. Viable sintering, processing and infiltration methods were outlined and compared. The introduction of the monolithic ZrB2-ZrSi2 system into C/C-SMP-10 construction achieved improved strength and high temperature performance via surface passivation and consolidation of the fibre-matrix interface. Through the use of XRD, SEM and microscopy the presence of passivating films and oxides were confirmed. High temperature experiments demonstrated a large improvement in mass retention from 68% to 83% in an inert atmosphere at 1600°. The new material system also significantly outperformed existing compositions in a 1000° oxidising environment. Future investigations into Zr-Si interactions with other refractory element additions is expected to make further improvements to create the next generation of ultra-high temperature performance materials.