Name: Zirconium Diboride (ZrB2/SiC)
Database: NASA Ames Thermal Protection Materials
Category: Ultra-High Temperature Ceramics
Composition: Zirconium Diboride(ZrB2) with 20 volume percent of a Silicon Carbide (SiC) particulate phase.
Manufacturer: There are no current commercial manufacturers of the UHTC materials.
Technical Readiness Level: 3
Last Modified: 2001-10-01

Description:

• These UHTC materials were fabricated by uniaxial hot pressing powder mixtures of ZrB2 and SiC. After mixing the powders were loaded into graphite dies for hot pressing. The dies were lined with pyrolytic graphite paper that was coated with a boron nitride wash. Hot pressing was conducted in an inert atmosphere at temperatures between 1800¡C and 2200¡C and pressures between 2500 to 4000 psi for 1 to 5 hours. The resulting composites attained greater than 98% of theoretical density with an average grain size of ~8 mm. The material properties are relatively isotropic with no significant orientation dependence induced by the uniaxial hot pressing. Studies have indicated that the SiC improves the oxidation resistance of the composite compared to that of pure ZrB2. The UHTC materials are have sufficient electrical conductivity to allow components to be machined by EDM. Currently NASA Ames Research Center has active programs on the processing, characterization and development of these materials for TPS applications, such as sharp leading edges on next generation reusable launch vehicles. <BR><BR> All UHTC material property data are from samples produced by MANLABS, INC. under contract to the air force and published in a series of technical reports (AFML-TR-68-190).

Point of Contact:

• Donald T. Ellerby
• NASA Ames Research Center
• dellerby@mail.arc.nasa.gov

Pictures:

• Diboride and RCC Specimens
• Micrograph Zirconium Diboride
• Diboride Samples

Notes:

• 1. Values calculated based on expansion data measured using comparative and direct observation dilatometry.
• 2. Up to 1000¡C: Thermal conductivity measurements were made using the comparative cut-bar method in an argon atmosphere fromm 100¡C to 1000¡C. Specimens were right circular cylinders 0.875 inches in diameter and 0.900 inches long with two 0.065 inch diameter holes drilled hal-way through the specimen centered 0.650 inches apart. Uncertainty due to error in measurements and procedures estimated to be +/-5%. <P>Beyond 1000¡C: Thermal Condcutivity was calculated from Thermal Diffusivity Measurements made using the flash-laser technique from 1000¡C to 2000¡C in argon. Samples were right circular cylindrical discs 0.500 inch diameter by 0.100 inch high with ends flat and parallel to +/-0.011inch. Uncertainty in measurement technique estimated to be +/-5% below 1800¡C and +/-8% above 1800¡C.
• 3. Specific heat calculated from enthalpy measurements made by drop calorimetry using a Bunsen ice calorimeter. Specimens were right circular rods 0.50 inche diameter and 2.00 inches long. Nominal uncertainty in specific heat values calculated using Bunsen calorimeter is +/-2%
• 4. Specimens: 0.050" x 0.100" x 0.875", elastic modulus measured in 4-pt bending in an argon atmosphere at constant strain rates between 7e-6/sec to 4e-4/sec.
• 5. Specimen: 0.100" x 0.200" x 1.75", 4-pt bend fixture, tested in argon atmosphere. Temperature measured using an optical pyrometer, temp was not corrected for sample emissivity. Typical strain rate: 3x10^-6/sec - 2x10^-6/sec. Tensile surface is perpendicular to the loading direction during hot pressing.
• 6. Specimen: 0.100" x 0.200" x 1.75", 4-pt bend fixture, tested in argon atmosphere. Temperature measured using an optical pyrometer, temp was not corrected for sample emissivity. Typical strain rate: 3x10^-6/sec - 2x10^-6/sec. Tensile surface is parallel to the loading direction during hot pressing. No significant directional dependence of strength data.
• 7. CTE calculated from linear expansion measurements using a Direct-View Dilatometer. Specimen dimensions: 0.25 x 0.25 x 2-3 inches. Estimated uncertainty is +/-1%. Measured in an inert atmosphere.
• 8. Current electrodes were fitted to each end of the bar and TC's were fitted into each hole. Potential difference was measured across the test sample. Resistivity was calculated from the ratio of the measured potential differences, the standard resistance that was in series with the sample, and the samples dimensions. Specimens: 0.250" square rods, 2.00" long with 2 small holes (0.031" diameter) drilled 1.250" apart in the central section.

Property References:

• 1. W. H. Rhodes, E. V. Clougherty, and D. Kalish: Research and Development of Refractory Oxidation-Resistant Diborides, Part II, Volume IV: Mechanical Properties:Technical Report AFML-TR-68-190:Jan. 1970:TPSX Ref. #127.
• 2. E. V. Clougherty, K.E. Wilkes, and R. P. Tye: Research and Development of Refractory Oxidation-Resistant Diborides, Part II, Volume V: Thermal, Physical, Electrical and Optical Properties:Technical Report AFML-TR-68-190:Nov. 1969:TPSX Ref. #128.

General References:

• 1. E. V. Clougherty and F. M. Anthony: Research and Development of Refractory Oxidation-Resistant Diborides, Part II, Volume VII: Application Evaluations and Design Considerations:Technical Report AFML-TR-68-190:May-70:TPSX Ref. #44.
• 2. L. Kaufman: Calculation of Multicomponent Refractory Composite Phase Diagrams:NSWC TR 86-242:Prepared for the Naval Surface Weapons Center:TPSX Ref. #45.
• 3. J. Bull, D. Rasky and Capt. J. Karika: Characterization of Selected Diboride Composites:Proceedings of the 16th Conference on Metal Matrix, Carbon, and Ceramic Matrix Composites:January 12-15, 1992:TPSX Ref. #46.