Fracture and toughening mechanisms in SiC nanofiber reinforced SiC matrix nanocomposites with amorphous carbon coatings

Fracture behavior of SiC matrix nanocomposites reinforced by SiC nanofiber coated with amorphous carbon (a-C) coatings is studied via molecular dynamics simulations. The a-C coating plays a significant role in the tensile strength, and fracture energy of the nanocomposites. With increasing thickness of the a-C coating, the failure behavior of nanocomposites transitions from brittle fracture to a non-catastrophic mode of ductile performance while the tensile strength increases. An introduction of appropriate functionally-graded a-C coating can significantly enhance nanofiber pullout and thus pullout energy by an order of magnitude. Our results suggest that material design directions — coating thickness and the functionally-graded coating — are all efficient approaches for engineering nanoscale SiC/SiC composites for high strength and toughness.