Thermal shock and ablation resistance of ZrB2-ZrC-Al2O3 composite coatings synthesized in situ by plasma spraying

Abstract

Zirconium boride composite coatings were synthesized in situ using atmospheric plasma spraying process with ZrO₂-B₄C-Al as precursor, and ZrB₂-ZrC-Al₂O₃ composite coatings were prepared as a comparison, and the microstructures and thermal shock and ablation resistance of the two systems of composite coatings were studied comparatively. The results showed that the ZrO₂-B₄C-Al system composite coating had higher density and ultra-fine microstructure, and this coating had better thermal shock resistance, which is mainly due to the reaction between the composite powders during the in-situ formation process of the coating, resulting in higher density and more stable phase structure. In the ablation test, a large amount of Al₄B₂O₉ was formed on the surface of the ZrB₂-ZrC-Al₂O₃ composite coating, which played the role of stabilizing the liquid phase and covered the surface of the coating to prevent the diffusion of oxygen, and the crystals grew and arranged preferentially to form a large-grained spherical oxidized eutectic phase as well as a solid solution of alumina and zirconia, so that the coating showed excellent ablation-resistant properties.