Oxidative Ablation Resistance Behavior Of Zr-based、Hf-based Ultra-high Temperature Ceramics

In recent years, hypersonic aircraft has attracted more and more attention and developed for military power all over the world due to its great military and economic value. It’s components in hot end put forward higher requirements for the materials, in order to adapt to this kind of environment, so ultra- high temperature ceramics materials become the focus of research development. The carbide and boride of Zr, the carbide and boride of Hf are the preferred materials for ultra high temperature conditions, because of the excellent high temperature performance. So the oxidation and ablation resistance properties in high temperature condition become the key indicator for these materials. In this paper, the samples of ZrC-SiC 、ZrB₂-SiC、HfC-SiC、HfB₂-SiC were ablated by the supersonic speed gas flow. The result is get the content of SiC and ablation temperature on the impact of rhe oxidation and ablation resistance performance and the ablative layer structure.As can be seen, ZrC-SiC、Zr B₂-SiC、HfC-SiC、HfB₂-SiC have good oxidation and ablation resistance. ZrB₂-SiC snd HfB₂-SiC have the lower ablation rate, the linear ablation rate and the mass ablation rate are all in the 10-5 mm·s-1 orders of magnitude, and the thickness of the ablator is less than 150 μm. ZrC-SiC、HfC-SiC’s ablation rate is more than boride, the mass ablation rate is in the 10-4 mm·s-1 orders of magnitude, and the ablator is thicker than boride. Because of oxide generated B₂O3 evaporation absorbing heat and the boride absorbing more heat in the process of oxidation, the boride surface temperature were higher than that of carbides. From the above, the boride have better oxidation and ablation resistance performance than carbides. Carbide ceramic’s ablation layer structure can be divided into three layers: surface layer is molten densely oxide layer, the second layer is SiO₂+ZrO₂/HfO₂, the third layer is partially oxidized layer. When SiC is less than 30% vol, there is recrystallized ZrO₂/HfO₂ layer under the surface due to the less SiO₂. Boride ceramic’s ablation layer structure also can be divided into three layers: surface layer is molten densely oxide layer, the second layer is SiO₂+ZrO₂/HfO₂, the third layer is SiC depletion layer. When SiC is less than 50% vol, there is recrystallized ZrO₂/HfO₂ layer. With the increase of ablation temperature, the ablation layer of ZrC-SiC、ZrB₂-SiC are a times thicker than before. But the impact of temperature on the thickness of HfC-SiC、HfB₂-SiC’s ablation layer is not big. For all samples, ablation layer structure become loose and combined with the matrix becomes poor with the increase of temperature. The SiC content have influence on oxidation and ablation resistance performance. The sample which have 70% vol SiC have the thinner ablation layer and the better ablation resistance performance because of the SiO₂ glass for oxygen barrier. And the surface of 50% vol SiC and 30% vol SiC are molten densely oxide layer, whose oxygen resistance ability are less than SiO₂, which ablation layer are thicker than 70% vol SiC.