Microstructure and high temperature anti-ablation behavior of Cr-modified ZrC coating for SiC-coated carbon/carbon composites

Abstract

To further the anti-ablation property of carbon/carbon composites (C/Cs) at extreme-high temperature, Cr-ZrC coating is fabricated on SiC-coated C/Cs. The anti-ablation properties of the ZrC coatings modified by various content of Cr are tested by oxyacetylene flame (heat flux: 2.4 MW/m2). Compared with pure ZrC coating, the ablation resistance property of the sprayed Cr-ZrC coating indicates an effective improvement. Cr acts as an accelerant by facilitating the liquid ZrO2 sintering and form a close structure. This dense structure can alleviate oxygen penetration. As the content of Cr increase (10 wt%, 15 wt% and 20 wt%), after cooling can also detect the retaining of tetragonal-ZrO2 (t-ZrO2). The phase transformation from t-ZrO2 to monoclinic ZrO2 (m-ZrO2) can lead to the volume expansion. The retaining of t-ZrO2 shows the phase transformation is impeded, which contributes to the thermal stability of the Cr modified ZrC coating. In the specimen, oxygen mainly diffuse through micropores, microcracks and grain boundaries. For Cr-ZrC coating, these diffuse ways could be partly or completely sealed by melted Zr-O-Cr coating during ablation test, which can effectively protect C/Cs during the oxyacetylene ablation test. When the content of Cr is 15 wt%, on the surface can form dense dendritic structure, which can effectively protect C/Cs from ablation.