To furtherly improve the ablation resistance of C/C-SiC-ZrC composites,ZrB2 ultrafine powder-modified C/C-SiC-ZrC composites were prepared by the reactive melt infiltration(RMI)method.The effects of ZrB2 ultrafine powder contents on the microstructure and ablation properties of modified composites were investigated.The results show that the introduction of ZrB2 ultrafine powder significantly increases the density of C/C-SiC-ZrC composites from 2.25 g/cm3 to 2.40-2.48 g/cm3,compared to the unmodified C/C-SiC-ZrC composites.ZrB2 is mainly observed in the ZrC matrix and exhibits uniform distribution.The addition of ZrB2 ultrafine powder significantly improves the ablation resistance of the composites.After 120 s of spark plasma ablation,the composites exhibites the lowest mass and linear ablation rates of 6.90 mg/s and 2.26 μm/s,respectively,when the ZrB2 ultrafine powder mole fraction is 2％.During the ablation process,the oxidized ZrO2 adheres to the composites'surface,forming a tortoiseshell-like ZrO2-SiO2 oxide layer with SiO2,which exhibits a certain degree of fluidity.The oxide layer reduces the diffusion and heat transfer of plasma to the matrix during the ablation process,which effectively improves the ablation resistance of modified composites.
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