Ultra-High Temperature Ceramics at University of Missouri-Rolla

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1 Ultra-High Temperature Ceramics at University of Missouri-Rolla Bill Fahrenholtz and Greg Hilmas Materials Science and Engineering University of Missouri-Rolla

2 The Need for UHTCs Ultra-high temperature ceramics are a unique class of materials Extremely high melting temperatures (>3000 C) Stable in reactive environments UHTCs are needed for use in extreme environments Reusable atmospheric re-entry vehicles Hypersonic flight vehicles Rocket propulsion X43B hypersonic flight vehicle Photo courtesy of NASA X33 reusable launch vehicle Photo courtesy of NASA

3 High Strength ZrB 2 -SiC ZrB 2 -SiC ceramics with strength >1000 MPa have been produced Strength improvement was attributed to control of grain size, minimization of imputies, and uniform distribution of SiC ZrB 2 SiC 10 µm Four point bend strength was ~1 GPa for ZrB 2 containing 30 vol.% SiC An average grain size of ~3 µm was measured for ZrB 2-30% SiC. The SiC particulates are uniformly distributed

4 Pressureless Sintering of ZrB 2 Dense (>98%) ZrB 2 has been prepared by sintering Most materials produced by hot pressing Sintering processes are necessary to enable scale-up and production Hot pressed components must be machined Machining can account for >50% of the cost of a component 20 µm Average grain size is ~10 µm compared to ~6 µm for hot pressed ZrB 2 Sintered ZrB 2 had an average strength of ~500 MPa, compared to ~550 MPa for ZrB 2 produced by hot pressing

5 Control of Fracture Behavior UHTCs with engineered meso-scale architectures have been fabricated Co-extrusion processing was used to form fibrous monolithics Non-brittle (graceful) failure behavior has been demonstrated Load retention after crack initiations ZrB 2 -SiC Cells ZrB 2 -SiC Cells Porous ZrB 2 Cell Boundaries An UHTC fibrous monolithic ceramic with ZrB 2 -SiC cells and porous ZrB 2 cell boundaries 500 µm The powder processed ZrB 2 -based FM showed failure behavior similar to that of a fiber-reinforced ceramic matrix composite

6 Current Programs Air Force Office of Scientific Research Reactive Processing and Co-Extrusion of ZrB 2 Ceramics Adam Chamberlain and Jim Zimmermann U.S. Army Space and Missile Defense Command Processing-Microstructure-Property Relations in SiC Andrew Buchheit, Xiaohong Zhang Air Force Research Laboratory Pressureless Densification of ZrB 2 Shi Zhang Advanced Ceramics Research Tantalum Carbide Ceramics Sean Landwehr National Science Foundation Reactive Processing of High Temperature Materials Alireza Rezaie and Stefanie Ricca

7 Recent UHTC Publications A.L. Chamberlain, W.G. Fahrenholtz, and G.E. Hilmas, Pressureless Sintering of ZrB 2, in preparation W.G. Fahrenholtz, The ZrB 2 Volatility Diagram, Submitted to the Journal of the American Ceramic Society, April A.L. Chamberlain, W.G. Fahrenholtz, G.E. Hilmas, and D.T. Ellerby, Oxidation of ZrB 2 -SiC Ceramics Under Atmospheric and Reentry Conditions, Accepted for publication in Refractory Applications Transactions, February A.L Chamberlain, W.G. Fahrenholtz, G.E. Hilmas, and D.T. Ellerby, High Strength ZrB 2 -Based Ceramics, Journal of the American Ceramic Society, 87(6) (2004). W.G. Fahrenholtz, G.E. Hilmas, A.L. Chamberlain, and J.W. Zimmermann, Processing and Characterization of ZrB 2 -Based Monolithic and Fibrous Monolithic Ceramics, Journal of Materials Science, 39(19) (2004). (UMR photo selected for cover of issue) A.L. Chamberlain, W.G. Fahrenholtz, G.E. Hilmas, and D.T. Ellerby, Characterization of Zirconium Diboride Ceramics for Thermal Protections Systems, Key Engineering Materials, , (2004). A. Chamberlain, W.G. Fahrenholtz, G.E. Hilmas, and D.T. Ellerby, Characterization of Zirconium Diboride- Molybdenum Disilicide Ceramics, pp in Advances in Ceramic Matrix Composites IX, Ceramic Transactions, Volume 153, ed. by N.P. Bansal, J.P. Singh, W.M. Kriven, and H. Schneider, The American Ceramic Society, Westerville, OH (2003).

8 UMR Capabilities Processing Equipment 2 graphite element hot presses capable of ~2200 C 1 graphite element sintering furnace capable of ~2200 C High shear mixers, laminating presses and ram extruders for processing of fibrous monolithic ceramics Characterization Facilities Field emission SEM/EDS with ~2 nm resolution DTA/TGA with mass spectrometry up to 1550 C Philips analytical electron microscope with EDS capability Surface analysis by XPS, AES, and grazing incidence XRD Property Evaluation Screw driven and hydraulic load frames for mechanical testing Four point bend strength testing up to 1500 C in air Hardness and elastic modulus measurement equipment