Synthetization of Refractory/Transition Metal Diboride & Carbide Precursors for Chemical Vapor Infiltration (CVI) of Ceramic Composites

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics OBJECTIVE: Develop a stable, scalable synthesis route for a refractory diboride precursor suitable for evaporation in a Chemical Vapor Infiltration (CVI) system. DESCRIPTION: Properties of refractory/transition metal diborides have attractive coating options for extreme applications with melting temperatures above 3200 C, high hardness, and excellent thermal oxidation resistance. Metal diborides such as hafnium, zirconium, tantalum, iridium, etc. have no commercially available single source CVI precursor. Depositing metal diboride via chemical vapor deposition routes such as CVI offer a viable method of integration into Ceramic Matrix Composite (CMCs) with respect to protective interface coatings. Commercial availability of refractory metal boride precursors to support epitaxial deposition is non-existent and development efforts are scarce. This STTR topic aims to develop stable, repeatable and scalable routes for new precursors for integration into existing large scale CVI systems. This research is critical for domestic development of key precursors identified to have the potential for significant advancements in Ultra High Temperature CMC processing. PHASE I: Demonstrate synthesis route and basic precursor properties (vapor pressure, melting/freezing temperature, density, etc.) using modeling, characterization and experimentation. Determine repeatable and projected scalability of formulation. PHASE II: Optimize process and demonstrate repeatability. Determine projected scalability of compound formulation. Begin Chemical Vapor Deposition (CVD) deposition studies. Evaluate deposition temperature range for amorphous and crystalline coatings and associated data showing crystallinity, grain size and stoichiometry. Initiate infiltration studies. PHASE III DUAL USE APPLICATIONS: Continue infiltration studies, modelling the infiltration process to determine optimal conditions (T, P, flow) to optimize densification of fiber preforms. Determine methods and measures to ensure reproducibility for scaling to larger preform sizes. Dual use activities could include commercial access to space components, as well as other high temperature applications in the energy and materials processing communities. REFERENCES: Coltelli, Maria Beatrice and Lazzeri, Andrea. Chemical vapour infiltration of composites and their applications. Chemical Vapour Deposition (CVD): Advances, Technology and Applications, CRC Press, July 2019, p. 363. https://www.routledge.com/Chemical-Vapour-Deposition-CVD-Advances-Technology-and-Applications/Choy/p/book/9780367780111# Aguirre, Trevor G.; Lamm, Benjamin W.; Corson L. Cramer, Corson L. and Mitchell, David J. Zirconium-diboride silicon-carbide composites: A review. Ceramics International, Volume 48, Issue 6, 15 March 2022, pp. 7344-7361. https://doi.org/10.1016/j.ceramint.2021.11.314 KEYWORDS: Precursors, coatings, chemical vapor deposition, chemical vapor deposition, organometallics, ceramic matrix composites