Study on fracture toughness and impact toughness of SiCf/SiC composites

SiCf/SiC composites were prepared through polymer impregnation and pyrolysis process using different mass fractions of liquid hyperbranched polycarbosilane and conventional solid polycarbosilane mixed precursors as impregnants. The microstructure and impact resistance of SiCf/SiC composites were characterized by scanning electron microscopy, fracture toughness, and impact toughness tests. Results showed that when the content of liquid hyperbranched polycarbosilane in the mixed precursor was not more than 60%, the number of fibers pulled out after impact fracture of SiCf/SiC composites under external load was large, the pull distance was long, and most of the fibers were successive fracture, presenting typical pseudoplastic fracture morphology. When the mass fraction of liquid hyperbranched polycarbosilane was equal to 40%, the fracture toughness and impact toughness both reached the optimum values. Under the optimized process conditions, the interface layer was gradually dissociated, and the fibers were successively bridged and pulled out, releasing a large amount of internal stress, which was helpful to improve the impact resistance of SiCf/SiC composites.