Sealing role of Ti-rich phase in HfC-ZrC-TiC coating for C/C composites during ablation above 2100 °C

Abstract

Traditional HfC, ZrC, and HfC-ZrC coatings cannot resist long-term ablation above 2100 °C because their oxides (HfO2 and ZrO2) express a loose structure and poor anti-oxygen infiltration ability after ablation. While Ti-rich oxides with a lower melting point can seal this loose structure during ablation. In this work, a HfC-ZrC-TiC multi-phases coating was proposed to solve the ablation failure problem of these coatings. It was prepared by supersonic atmospheric plasma spraying and tested by ablation with a heat flux of 2.38 MW/m2. With time ranging from 30 s to 120 s, the mass and linear ablation rates decreased from 0.85 mg/s to 0.18 mg/s and from 2.58 µm/s to 0.71 µm/s, respectively. All positive values indicated an increase in all coating thicknesses, so this coating can effectively protect C/C composites for more than 120 s. The surface of the coating was mainly composed of a loose oxide m-(Hf, Zr, Ti)O2 skeleton within 120 s. As oxide skeletons had been gradually destroyed by mechanical denudation, the liquid phase of (Hf, Zr)TiO4 was formed under oxide skeletons to fill pores. Then the surface of the oxide layer was dense after 120 s. The self-healing ability of the HfC-ZrC-TiC coating improved the ablation resistance of C/C composites above 2100 °C.