B. Dyatkin, M. Laskoski, B.Y. Rock, S. Qadri, M. Kolel-Veetil, T.M. Keller, R.M. Gamache
U.S. Naval Research Laboratory,
Keywords: ceramic, sintering, armor, polymer-derived ceramic, nanomaterial, carbon-ceramic composite, hypersonic engines
Summary:Ultra-high temperature ceramics (UHTCs) and refractory carbides with high hardness and oxidation resistance demonstrate significant promise in armor and hypersonic engine applications. However, to date, they have been too brittle and expensive to widely implement on an industrial scale. Our efforts report on new approaches to synthesize and sinter boron carbides, silicon carbides, and zirconium carbides. We incorporate elemental inclusions, heterogeneous carbide phases, and carbon allotropes into carbides to improve the strength and shock resistance of the resulting composites. This nanostructuring approach uses commercially viable high-energy ball milling and slurry dispersion methods and yields powders, monoliths, and coatings of optimized ceramics. We report on the resulting structure and properties of these optimized UHTCs. We developed a novel synthesis route that synthesizes shaped carbides from compressed powder mixtures of metal precursors and a carbon resin (1,2,4,5-tetrakis(phenylethynyl)benzene, or TPEB). This one-step approach yields dense ceramics with application-specific shapes such as disks and spheres and relies on pressureless tube furnace synthesis at temperatures below 1,500 °C. We report on the structure and synthesis and demonstrate processing modifications steps that produce nanostructured composites with tunable electronic and thermal conductivity properties. In an alternative to energy-intensive and commercially inefficient hot pressing, we present a sintering approach that irradiates greenbody ceramics with microwaves to densify metal carbides. This flash sintering method rapidly compacts boron carbides and yields highly dense (over 90% of TMD) structures. This technique requires shorter sintering times (< 30 minutes) and temperatures (< 1,300 °C), which improves the commercial viability of B4C in a broad range of commercial and military applications. References: 1. Kolel-Veetil, M. K., Gamache, R.M., et al. Substitution of silicon within the rhombohedral boron carbide (B 4 C) crystal lattice through high-energy ball-milling. Journal of Materials Chemistry C, 3(44), 11705-11716 (2015). 2. Keller, Teddy M., Manoj K. Kolel-Veetil, and Syed B. Qadri. "Pyrolytic formation of metallic nanoparticles." U.S. Patent No. 7,700,710 (2010). 3. Goswami, Ramasis, et al. "Insertion of elements within boron carbide." U.S. Patent Application No. 15/093,737.