Physical characterization and arcjet oxidation of hafnium-based ultra high temperature ceramics fabricated by hot pressing and field-assisted sintering

摘要

For this study, HfB_2-based ultra high temperature ceramic (UHTC) samples were prepared by hot pressing and field-assisted sintering (FAS) with 10-20 vol.% SiC (baseline), 5 vol.% TaSi_2 , and 5 vol.% iridium. Dense billets were tested for hardness and mechanical strength. When compared, theFAS method consistently yielded materials with a grain size 1.5-2 times finer than samples processed via hot pressing. In general, room temperatureflexural strengths of these materials were found to be lower (～400 MPa) than similar fully dense HfB2- SiC materials, with strengths between 500 and 700 MPa. Oxidation resistance testing of flat-face models was conducted in a simulated re-entry environment, at Qcold Wall ～250W/cm~2 min. Samples processed by FAS had reduced oxide thickness and SiC depletion zones compared to the baseline HfB_2-20SiC material. In allcases oxide thickness was reduced by ～3 × and SiC depletion zone thickness was reduced ～3 × over the baseline.