The oxidation behavior of an ultra-high temperature ceramic (UHTC) based on HfB2 with 20vol% SiC and was studied following two 10 min arc-jet test cycles with nominal heat flux of 350 W cm−2, stagnation pressure of 7 kPa, and a sustained peak surface temperature of 2360 °C. Microstructure characterization revealed a modified, layered structure comprising ∼390 μm of porous HfO2 at the surface and an underlying ∼740 μm porous region containing un-oxidized HfB2 over the bulk UHTC, unaffected below the oxidation front. The SiC presumably undergoes active oxidation, as commonly reported for temperatures above ∼1600 ± 100 °C. However, unlike typical of exposures below ∼2000 °C no molten silicate phase was present at the surface to mediate the exchange of oxidant and gaseous reaction products. Additionally, a HfC impurity phase oxidizes concurrently with SiC rather than HfB2. A thermodynamic analysis is provided to explain the observed behavior and the differences with lower temperature scenarios in the literature.
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of the European Ceramic Society|
|State||Published - Nov 1 2016|
Bibliographical noteFunding Information:
This investigation was sponsored by the Office of Naval Research under MURI Grant N00014-05-1-0439 , monitored by Dr. Julie Christodoulou, with additional support from grant N00014-14-1-0625, monitored by Dr. David Shifler. The authors are grateful to Dr. Sylvia Johnson, from NASA Ames, for providing the UHTC specimens. The work made use of the MRL Shared Experimental Facilities supported by the MRSEC Program of the NSF under Award No. DMR 1121053 ; a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org).
© 2016 Elsevier Ltd
- Hafnium boride
- Hafnium carbide
- Silicon carbide
- Ultra high temperature ceramic