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 (UHTC), composed primarily of metal diborides, are candidate materials for sharp leading edges on hypersonic re-entry vehicles. 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. 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.
UHTCs are a family of ceramic materials with very high melting temperatures and reasonable oxidation resistance in reentry environments. Ground-based arc-jet testing has demonstrated their potential for applications at temperatures approaching 4000 °F, or 2200 °C. This invention generally relates to ceramic compositions and processes for obtaining a ceramic product, especially UHTCs. It specifically targets consolidated ceramic composites comprising a microstructure of a ceramic matrix that incorporates a reinforcing ceramic phase with a uniform distribution of the reinforcing phase, and controlling the growth of these phases.
A tough UHTC composite comprises grains of UHTC matrix material, such as HfB2 or other metal boride, carbide, or nitride. These are surrounded by a uniform distribution of acicular high-aspect-ratio reinforcement ceramic rods or whiskers, such as SiC, that are formed from uniformly mixing a powder of the UHTC material and a pre-ceramic polymer selected to form the desired reinforcement species. The mixture is then thermally consolidated by hot pressing.
This technology could potentially be used in re-entry vehicles for aerospace and defense applications, reusable launch vehicles, hypersonic vehicle leading edges, and commercial spacecraft for enhanced aerodynamic performance.