Toughening in ceramics containing graphene fillers

Abstract High level of reinforcement is observed in ceramic matrix composites containing multilayer graphene, which is frequently attributed to bridging and pull-out phenomena based on microstructural observations of crack paths. Presently, we show that the toughening level observed in two ceramic matrix composites with different graphene type fillers is reasonably fitted to the well-known model for reinforcement of ceramic composites by whiskers/fibers. Furthermore, the most important toughening contribution for these composites is due to bridging by the graphene fillers. The model predicts a steady toughness increment as a function of filler volume but for filler volume concentrations close to the percolation threshold the experimentally observed reinforcement deviates from the model predictions and toughness starts to decay. Consequently, once graphene fillers are fully connected forming a three dimensional network bridging the graphene fillers stops being an effective toughening mechanism.