T. Butler, B. Dyatkin, S.M. Deese, M. Laskoski
U.S. Naval Research Lab,
Keywords: ceramics, composites, high-char yield resins, thermosets
Summary:Advancements in high-speed propulsion systems have spurred demand for materials which can withstand the harsh conditions necessitated by this hypersonic travel. Ultra-high temperature ceramics (UHTCs) such as transition metal borides, nitrides, and carbides melt at temperatures greater than 3000 °C, thereby exceeding the temperature threshold required for hypersonic applications. However, these materials are quite brittle which leads to low fracture toughness, and poor thermal shock resistance. In addition, the extensive synthesis and processing that is required to produce UHTC materials with shapes machined for specific applications substantially increases their production costs. To this end, a variety of reinforced UHTC materials were synthesized using polymeric method to fabricate ceramic phases in situ enabling the production of near-net-shape composites. This method exploits the chemical reaction between elemental metals or metal hydrides and a high char-yield polymeric resins—which acts as a carbon source, as well as a binding phase—to produce low-cost composite materials. Using this strategy, ceramic materials with short-chopped reinforcement phases were fabricated from several resin systems including 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB). For samples made with TPEB, crosslinking between acetylene groups occurs when heated in excess of 200 °C, which resulted in the formation of a static thermoset with reinforcement and ceramic phases homogeneously dispersed throughout the greenbody. Alternatively, precursor slurries was used to impregnate woven fabric preforms to form continuous fiber composites reinforced with varying concentrations of metal carbide phases. Fabrication of UHTC composites using this polymeric method improves their commercial viability via lowering production costs and enhancing processability.