EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Fully-dense ZrB₂ and HfB₂ samples were elaborated by SPS with three different additive compounds such as SiC, TaSi₂ or AlN (20 vol.%) to improve the oxidation resistance of the composite. To prevent grain growth during densification, sintering parameters were optimized following the process described by Piriou et al. [1].
Oxidation in air plasma from 1800 up to 2600 K was studied using the MESOX facility implemented at the focus of the 6 kW Odeillo solar furnace in presence of atomic oxygen up to 80%. The experimental parameters were set to partially reproduce the atmospheric re-entry conditions on Earth. The mass variation of the samples oxidized during 300 s on a temperature plateau in air plasma at 1000 Pa total air pressure was followed. Above 1950 K, a significant mass loss is observed for composites with SiC addition followed by a plateau of around 200 K with a constant mass loss up to 2250 K. Then a new significant mass loss is observed up to 2650 K. The mass loss is lower for the composite containing TaSi₂ with a different trend with temperature. Samples with AlN seem to reveal the best behavior with a significant mass gain. The ZrB₂-20%AlN composite seems promising at this point of the study. Overall, zirconium-based composites present a better behavior under oxidation at high temperatures in air plasma conditions compared to hafnium-based composites. Material characterization using SEM, XRD and Raman spectroscopy was carried out to understand the oxidation phenomena at such high temperatures.

[1] Piriou C. et al., Ceram. Int. 45, 2019, 1846-1856.