Ultra high temperature ceramics for hypersonic vehicle applications.

Tandon, Rajan ; Dumm, Hans Peter ; Corral, Erica L. ; Loehman, Ronald E. ; Kotula, Paul Gabriel

Sandia National Laboratories

关键词: Specific Heat;    Ceramics.;    Thermal Conductivity;    Silicon Carbides;    Flexural Strength;   

DOI  :  10.2172/887260
RP-ID  :  SAND2006-2925
RP-ID  :  AC04-94AL85000
RP-ID  :  887260

美国|英语

来源: UNT Digital Library

【 摘 要 】

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.