Ultra high temperature ceramics for hypersonic vehicle applications.
HfB{sub 2} and ZrB{sub 2} are of interest for thermal protection materials because of favorable thermal stability, mechanical properties, and oxidation resistance. We have made dense diboride ceramics with 2 to 20 % SiC by hot pressing at 2000 C and 5000 psi. High-resolution transmission electron microscopy (TEM) shows very thin grain boundary phases that suggest liquid phase sintering. Fracture toughness measurements give RT values of 4 to 6 MPam{sup 1/2}. Four-pt flexure strengths measured in air up to 1450 C were as high as 450-500 MPa. Thermal diffusivities were measured to 2000 C for ZrB{sub 2} and HfB{sub 2} ceramics with SiC contents from 2 to 20%. Thermal conductivities were calculated from thermal diffusivities and measured heat capacities. Thermal diffusivities were modeled using different two-phase composite models. These materials exhibit excellent high temperature properties and are attractive for further development for thermal protection systems.
- Research Organization:
- Sandia National Laboratories
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 887260
- Report Number(s):
- SAND2006-2925
- Country of Publication:
- United States
- Language:
- English
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INVESTIGATION OF BORIDE COMPOUNDS FOR VERY HIGH-TEMPERATURE APPLICATIONS
Calculation of multicomponent refractory-composite phase diagrams. Final report, 1 January-1 June 1986
Related Subjects
Ceramic materials-Fracture.
Ceramics.
FLEXURAL STRENGTH
FRACTURE PROPERTIES
HAFNIUM BORIDES
HOT PRESSING
MATHEMATICAL MODELS
Materials-Thermal properties.
SILICON CARBIDES
SPECIFIC HEAT
THERMAL CONDUCTIVITY
THERMAL DIFFUSIVITY
THERMAL INSULATION
Thermal analysis.
ZIRCONIUM BORIDES