Comparison Between Carbon Nanotube and Carbon Nanofiber Reinforcements in Amorphous Silicon Nitride Coatings

Amorphous silicon nitride coatings were reinforced with carbon nanotubes and dense carbon nanofibers. These reinforcements were all fabricated with graphene layers oriented parallel to the fiber axis, and some of the nanofibers were also heat-treated at high temperature to improve graphitic ordering. The effectiveness of these reinforcements as toughening agents was then compared qualitatively by examining the fiber pull out lengths from fracture surfaces. With the dense nanofibers there was almost no evidence of pull-out, whereas the materials reinforced with multiwalled carbon nanotubes exhibited significant pull-out. Based on these results, the multiwalled carbon nanotubes appear to provide significantly more toughening than the dense nanofibers.