Microstructure and fracture toughness of Si_3N_4 + graphene platelet composites

摘要

Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPLs) as filler. The influence of the addition of GPLs on the microstructure development and on the fracture toughness of Si_3N_4 + GPLs composites was investigated. The GPLs with thickness from 5 nm to 50 nm are relatively homogeneously distributed in the matrix of all composites, however overlapping/bundle formation of GPLs was found, containing 2-4 platelets as well. The single GPLs and overlapped GPLs are located at the boundaries of Si_3N_4, and hinder the grain growth and change the shape of the grains. The fracture toughness was significantly higher for all composites in comparison to the monolithic Si_3N_4 with the highest value of 9.9 MPam~(0.5) for the composite containing the GPLs with smallest dimension. The main toughening mechanisms originated from the presence of graphene platelets, and responsible for the increase in the fracture toughness values are crack deflection, crack branching and crack bridging.