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

For this study, HfB2-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.% TaSi2, and 5 vol.% iridium. Dense billets were tested for hardness and mechanical strength. When compared, the FAS method consistently yielded materials with a grain size 1.5–2 times finer than samples processed via hot pressing. In general, room temperature flexural 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 ∼250 W/cm2 for 5 min. Samples processed by FAS had reduced oxide thickness and SiC depletion zones compared to the baseline HfB2–20SiC material. In all cases oxide thickness was reduced by ∼3× and SiC depletion zone thickness was reduced ∼3× over the baseline.