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HfC coating

Time:2019-08-05 18:23:10  From:  Author:

 Among all of the refractory metal carbides, HfC is characterized by the highest melting temperature (3959 °C) , high mechanical properties, good resistance to chemical attack and ablation, and high temperature phase stability . In addition, the melting point of HfO2 is 2810 °C, which is higher than that of ZrO2 (2667 °C) and Ta2O5 (1800 °C). So, from the perspective of thermal stability, HfC is a promising coating material to protect C/C composites from ablation in severe ablation environment. During ablation, HfC coating will be oxidized to porous HfO2 layer. The pores in the oxide coating will provide penetration channels for oxygen. In addition, the chalked oxide coating will easily peel off from C/C substrate. Introducing carbides with lower melting point as the second phase could improve the oxidation resistance of HfC ceramic . Xiong et al. synthesized HfC/ZrC biphasic coating on C/C composites by chemical vapor deposition (CVD), results showed that ZrC could improve the ablation resistance of HfC coating. Wang et al. synthesized Hf(Ta)C coating by CVD, which indicated that a dense and continuous Hf6Ta6O17 glassy layer was generated during ablation, which could inhibit the oxygen infiltration and improve the ablation resistance of the coating. Yang et al. [20] prepared HfC-SiC coating by supersonic atmospheric plasma spraying (SAPS), results indicated that a Hf-Si-O compound oxide layer was formed during ablation, which could restrain the oxygen penetration. So, introducing carbide with lower melting point as the second phase could improve the ablation resistance of HfC coating.

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