HFB2 and ZrB2 ceramics CS applications

HfB2 and ZrB2 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 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 ZrB2 and HfB2 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.

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