Future-generation materials for use on space transportation vehicles require substantial improvements in material properties, leading to increased reliability and safety, as well as intelligent design to allow for current materials to meet future needs. Ultra-high-temperature ceramics (UHTCs) composed primarily of metal diborides are candidate materials for sharp leading edges on hypersonic re-entry vehicles. The mechanical performance of ceramics in general would benefit from a high-aspect reinforcement phase.
NASA has demonstrated that it is possible to form high-aspect-ratio reinforcement phases in situ during the processing step for both ceramic composites and UHTCs. For example, preliminary results on obtaining high-aspect-ratio particulate SiC reinforcements in UHTC materials using a novel chemistry approach combined with hot pressing have been successful.
Initial characterization of these systems has demonstrated that crack deflection along the matrix-reinforcement interface is observed, yielding a system of improved toughness over the baseline system, leading to improved mechanical performance. The reinforced composites should therefore reduce the risk of catastrophic failure over current UHTC systems.
The invention generally relates to ceramic compositions and processes of obtaining a ceramic product, especially ultra-high-temperature ceramics. It specifically relates to consolidated ceramic composites comprising a microstructure of a ceramic matrix incorporating a reinforcing ceramic phase with a uniform distribution of the reinforcing phase and controlling the growth of these phases.
A tough UHTC composite is comprised of grains of UHTC matrix material, such as HfB2 or other metal boride, carbide, nitride, etc. These are surrounded by a uniform distribution of acicular high-aspect-ratio reinforcement ceramic rods or whiskers, such as SiC, formed from uniformly mixing a powder of the UHTC material and a pre-ceramic polymer selected to form the desired reinforcement species, then thermally consolidating the mixture by hot pressing.
UHTCs are ceramic materials with very high melting temperatures and reasonable oxidation resistance in re-entry environments. Ground-based arc-jet testing has demonstrated their potential for applications at temperatures approaching 4,000 °F (≈2,200 °C).