Oxidation resistance up to 2600 K under air plasma of (Zr/Hf)B2 composites containing 20 vol% AlN for hypersonic applications

Fully-dense ZrB₂ and HfB₂ composites were elaborated by Spark Plasma Sintering with 20 vol% AlN to replace SiC or TaSi₂ with the objective to improve the oxidation resistance at very high temperature. This study follows the ones on (Zr/Hf)B₂-SiC and (Zr/Hf)B₂-TaSi₂ systems carried out in the same conditions (Pellegrini et al. 2022a; Pellegrini et al. 2022b). Oxidation behavior of several samples in air plasma conditions, at 1000 Pa total pressure and from 1980 K up to 2600 K, was studied using the MESOX facility implemented at the focus of a solar furnace. The mass variation of the samples during oxidation duration of 300 s on a temperature plateau was measured. The characterization of the oxidized samples was done using SEM, EDS, XRD, XPS and Raman. A better oxidation resistance was obtained with these new compositions as, for example, no mass loss up to 2600 K was measured for the ZrB₂-20 vol% AlN composite due to the protective effect of the aluminum-rich phase formed by oxidation and confirmed by the cross-section analysis.