Tailoring the geometry of silicon nitride nanofillers to simultaneously strengthen and toughen carbon/carbon composites

Incorporating one-dimensional(1D)nanofillers into carbon/carbon composites(C/Cs)can increase their mechanical strength.However,this method is ineffective in improving the fracture toughness of C/Cs be-cause cracks can easily pass over the 1D nanofillers,resulting in a flat fracture surface.Herein,we propose a new technique to significantly improve both the strength and toughness of C/Cs by incorporating 2D ribbon-shaped nanofillers.Silicon nitride nanoribbons(SiNNRs)are assembled into a film-like structure and inserted into each layer of a carbon fiber laminate,which is then densified with a pyrocarbon matrix.Due to the large interfacial contact area between the nanoribbon and matrix,ribbon-shaped SiNNRs can efficiently arrest and deflect cracks in both two and three dimensions,exhibiting a higher reinforcement efficiency than that of slender silicon nitride nanowires(SiNNWs).Mechanical tests show that the per-centage increases in fracture toughness,flexural strength,and compressive strength of C/Cs produced by SiNNRs are approximately 9.8,1.8,and 1.25 times higher than those produced by SiNNWs at the same volume fraction of nanofillers,respectively.This study suggests that 2D ribbon-shaped nanofillers are more effective than 1D fibrous nanofillers in enhancing the strength and toughness of C/Cs.