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Novel Polymer-Derived Carbide and Boride Refractory Ceramics

Description:

TECHNOLOGY AREA(S): Materials/Processes

OBJECTIVE: Demonstrate a preceramic polymer yielding a refractory metal boride and/or carbide to be used in the manufacture of ceramic matrices for the processing of ceramic matrix composites that can withstand temperatures in excess of 1600 degrees Celsius.

DESCRIPTION: Silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiC/SiC CMCs) are being utilized for turbine engine and structural aeroshell components capable of withstanding temperatures of 1300-1400 degrees Celsius. Their lower density, higher hardness, and improved thermal and chemical resistance when compared to metallic systems at the same temperature make CMCs attractive candidates for a range of propulsion and airframe applications. However, the requirement for higher Mach number and thus higher use temperatures for the development of hypersonic vehicles is driving the need for new materials and material systems with requisite lifetimes for thermal protection and propulsion components. Increasing the use temperature and/or lifetime of these materials will require that CMCs be manufactured from higher temperature capable matrices. Ceramics such as refractory metal carbides and borides (e.g., ZrC, HfC, TaC, ZrB2, HfB2, etc.) are candidate materials for these applications because of their high thermal conductivity and the high melting temperatures of both the base material and the solid oxidation product.

Conventional SiC matrix processing routes often require the use of preceramic polymers that rely on the ease of infiltration of a liquid or dissolved solid polymer that can be converted to a ceramic material after pyrolysis.[1] The polymers are often loaded with SiC powder to decrease the required number of re-infiltration steps and maximize final CMC density. Polymers can also be loaded with refractory carbide or boride powder, but powder loadings are limited to between 30 and 40 volume percent in order to maintain a slurry with viscosity to penetrate fiber weaves and tows.[2] Commercial sources of SiC preceramic polymers exist, but variants of other stoichiometric carbides and borides are scarce domestically. Limited fundamental work [3-5] has been conducted to prepare and analyze refractory metal carbide and boride precursors.

The goal of this topic is to synthesize novel chemistries and prove the capability of the preceramic polymers to form refractory carbide and/or boride ceramics. Characteristics of the polymer that are important to determining their viability in matrix processing include but are not limited to thermoset or thermoplastic behavior; solubility of the polymer in solvents and its compatibility with other preceramic polymers; and curing mechanisms including melting temperatures, cross-linking temperatures, and crystallization temperatures. Post-pyrolysis products should be understood with regard to degree of crystallinity, stoichiometry, and yield.

PHASE I: Identify a proof of concept for a preceramic polymer precursor that forms a refractory carbide and/or boride ceramic other than a Si-based ceramic upon pyrolysis with ceramic yields in excess of 60 volume percent. Demonstration of proof of concept must include X-ray diffraction and electron microscopy of the resulting material to verify chemical composition and crystalline structure.

PHASE II: Demonstrate and optimize a preceramic polymer for matrix processing with further characterization of the polymer including rheology, molecular structure, and cure mechanisms. Fabrication, characterization, and high temperature (>1600 degrees Celsius) oxidation testing of a CMC is expected.

PHASE III DUAL USE APPLICATIONS: Scale-up preceramic polymer for sale to the community of CMC developers, suppliers, and end users. Preceramic polymers are used in the DOD and commercial industry for production of CMCs and coatings for thermal protection systems, aircraft engine components, and nuclear shielding applications.

REFERENCES:

    • R. Jones, A. Szweda, and D. Petrak, “Polymer Derived Ceramic matrix Composites,” Composites Part A: Applied Science and Manufacturing, 30(4), 569-575, (1999).

 

    • C. Leslie, H. Kim, H. Chen, K. Walker, E. Boakye, C. Chen, C. Carney, M. Cinibulk, and M. Chen, “Polymer-Derived Ceramics for Development of Ultra-High Temperature Composites,” in Innovative Processing and Manufacturing of Advanced Ceramics and Composites II: Ceramic Transactions, 243 (2014).

 

    • S. Schwab, C. Stewart, K. Dudeck, S. Kozmina, J. Katz, B. Bartram, E. Wuchina, W. Kroenke, and G. Courtin. “Polymeric Precursors to Refractory Metal Borides,” Journal of Materials Science, 39(19), 6051-6055 (2004).

 

    • L. Sneddon, G. Larry, and S. Yang, “Chemical Routes to Ceramics with Tunable Properties and Structures: Chemical Routes to Nano and Micro-Structured Ceramics” F49620-03-1-0242, AFOSR (2005).

 

  • K. Inzenhofer, T. Schmalz, B. Wrackmeyer, and G. Motz, “The Preparation of HfC/C Ceramics via Molecular Design,” Dalton Transactions 40, 4741-4745 (2011).

KEYWORDS: polymer-derived ceramic, carbide, boride, ceramic matrix composite, preceramic polymer

  • TPOC-1: Carmen Carney
  • Phone: 937-255-9154
  • Email: carmen.carney.1@us.af.mil
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