Oxidation of ZrB{sub}2 ceramics modified with SiC and group IV-VI transition metal diborides

摘要

The oxidation resistance of non-oxide ceramics is highly dependent on the protective capabilities of an oxide layer formed on the surface of the sample exposed to oxygen-containing atmosphere. The addition of SiC to ZrB{sub}2 ceramics resulted in the significant increase in their oxidation resistance due to the formation of the protective layer of borosilicate glass. Further improvement in oxidation performance of the ZrB{sub}2/SiC ceramics was accomplished by the introduction of TiB{sub}2, NbB{sub}2, TaB{sub}2,VB{sub}2, and CrB{sub}2 as partial substitution (up to 20 mole%) for ZrB{sub}2. The presence of Zr, Ti, Nb, V, or Cr oxides in the surface borosilicate glass caused intensive phase separation (immiscibility) which was detected by SEM. The increased liquidus temperature and viscosity of immiscible glasses are considered responsible for the observed improvement in the oxidation resistance of the studied ceramics.