High-temperature oxidation and ablation behavior of plasma sprayed LaB6-MoSi2-TiB2 composite coating

Highlights: • Good adherence of LaB₆-MoSi₂-TiB₂ coating ascribed mechanical bonding with interlocking. • The incorporation of TiB₂ improved oxidation and ablation resistance of LaB₆-MoSi₂ coating. • Selective oxidation of La, Ti and Si suppressed the occurrence of pest oxidation. • The formation of La-Si-O-B-Ti compound scale ensured long-term stability of LaB₆-MoSi₂-TiB₂ coating. A combined heterogeneous coating composed of LaB₆-MoSi₂-TiB₂ (LMT) outer layer and SiC inner layer was fabricated on carbon/carbon (C/C) composites using a two-step method. Among them, the SiC transition layer was in-situ synthesized by pack cementation (PC) in the first step, where-after supersonic atmospheric plasma spraying (SAPS) was devoted to deposit the LMT outer layer. The combined LMT/SiC coating revealed a representative microstructure with limited porosity and adhered well with the C/C substrate. Isothermal oxidation test demonstrated that the combined LMT/SiC coating displayed a better oxidation resistance than the MoSi₂/SiC coating without the addition of rare-earth La and alloying Ti elements at 1773 K. Oxyacetylene torch experiment showed that the combined LMT/SiC coating could efficiently protect the C/C composites withstand short-term ablation for 60 s. The good oxidation and ablation resistant properties of the combined LMT/SiC coating were ascribed to the integrity of LMT/SiC coating and superior protection of a glassy La-Si-O-B-Ti compound scale formation during oxidation and ablation.