Effects of precursor concentration on the microstructure and properties of ZrC modified C/C composites prepared by precursor infiltration and pyrolysis

To improve the ablation resistance of C/C composites, ZrC modified composites were fabricated by precursor infiltration and pyrolysis combined with gradient chemical vapor infiltration process. The effects of ZrC precursor concentration on the microstructure, mechanical and ablation properties of the composites were studied. Results showed that with the increase of ZrC precursor concentration, the ZrC content and macroscopic uniformity of the composites increased but with obvious ZrC particle aggregation and the flexural strength decreased gradually. As the concentration of ZrC precursor improved to 60%, the fracture mode of the composites transformed from toughness to brittleness which was mainly attributed to the improved graphitization degree and reaction damage of carbon fiber in the precursor pyrolysis process. However, the ablation resistance was enhanced with the increasing precursor concentration which was resulted from the formation of ZrO₂ in center ablation region and continuous ZrO₂ coating in brim region serving as a barrier to heat and oxygen transfer.