Influence of processing on fracture toughness of Si3N4 + graphene platelet composites

Silicon nitride +1 wt% graphene platelet composites were prepared using various graphene platelets (GPL) and two processing routes; hot isostatic pressing (HIP) and gas pressure sintering (GPS). The influence of the processing route and graphene platelets' addition on the fracture toughness has been investigated. The matrix of the composites prepared by GPS consists of Si3N4 grains with smaller diameter in comparison to the composites prepared by KIP. The indentation fracture toughness of the composites was in the range 6.1-9.9 MPa m(0.5), which is significantly higher compared to the monolithic silicon nitride 6.5 and 6.3 MPa mm(0.5). The highest value of Km was 9.9 MPa m(0.5) in the case of composite reinforced by the smallest multilayer graphene nanosheets, prepared by HIP. The composites prepared by GPS exhibit lower fracture toughness, from 6.1 to 8.5 MPa m(0.5). The toughening mechanisms were similar in all composites in the form of crack deflection, crack branching and crack bridging. (C) 2013 Elsevier Ltd. All rights reserved.