Ablation resistant behavior of silicide modified HfB₂-SiC coating on graphite by spark plasma sintering: Role of MeSi₂ addition

The silicides (MeSi₂, Me = Ta, Zr, W, Mo) with strong Si supply capability are promising for improving the loose and porous HfO₂ skeletons from ablation resistant coatings for carbon-based materials. Herein, MeSi₂ modified HfB₂-SiC coatings prepared by spark plasma sintering were evaluated under oxyacetylene ablation condition (2.4 MW/m²) to analyze the protection mechanism. Experimental and theoretical analyses show that, MoSi₂ can be considered as the optimal Si additive and HfB₂-SiC-MoSi₂ coating exhibits the lowest linear variation rate of −0.19 μm/s. The by-product retention of WO_x and ZrO₂ derived from WSi₂ and ZrSi₂ will cause rapid thickening of Hf-Si-O layer, while the by-product (Hf₆Ta₂O₁₇) from TaSi₂ leads to severe consumption of HfO₂ skeleton (0.29 μm/s). The disparate mechanisms of MeSi₂ addition are jointly decided by the fluctuation of Hf-O bond length (0.219–0.229 nm) in Me modified HfO₂ solid solutions, as well as the differently dynamic consumption of MeO_x by-products.