Processing of Ultra-High Temperature Ceramics for Hostile Environments

Abstract

A detailed review of the processing of zirconium, hafnium, and tantalum based boride-carbide-nitride composites is presented. The processing methodology and important steps involved in producing a pore-free microstructure are reported. The effect of addition of secondary and ternary compounds on densification is highlighted as is the reactive processing of ultra-high temperature ceramics (UHTCs) based on zirconium carbide through the formation of a transient non-stoichiometric carbide and transient liquid phase, which enable densification at much lower temperatures. The reactive processing method is promising in that it readily leads to variation in the composition of secondary/ternary non-oxide phases in the composites as well as the incorporation of fibres which may otherwise degrade. Since the processing temperatures are lower, the grain size obtained after densification is finer and may lead to better mechanical properties (hardness, fracture toughness, and strength). Processing of fibre based composites with boride particulates and silicon carbide through the ceramic precursor route are also discussed.