Toughening in Graphene Ceramic Composites

TLDR

Graphene nanocomposites have largely been studied in polymer matrices, while ceramics, though ideal for high‑temperature use, suffer from low toughness. Here we report for the first time the use of graphene to enhance the toughness of bulk silicon nitride ceramics. Our approach uses graphene platelets homogeneously dispersed with silicon nitride particles and densified at ~1650 °C by spark plasma sintering, with parameters chosen to preserve the platelets as confirmed by Raman spectroscopy. The fracture toughness increased by up to ~235 % (from ~2.8 to ~6.6 MPa·m¹/²) at ~1.5 % GPL volume fraction, with cage‑like graphene structures wrapping grains that deflect cracks in three dimensions.

Abstract

The majority of work in graphene nanocomposites has focused on polymer matrices. Here we report for the first time the use of graphene to enhance the toughness of bulk silicon nitride ceramics. Ceramics are ideally suited for high-temperature applications but suffer from poor toughness. Our approach uses graphene platelets (GPL) that are homogeneously dispersed with silicon nitride particles and densified, at ∼1650 °C, using spark plasma sintering. The sintering parameters are selected to enable the GPL to survive the harsh processing environment, as confirmed by Raman spectroscopy. We find that the ceramic's fracture toughness increases by up to ∼235% (from ∼2.8 to ∼6.6 MPa·m1/2) at ∼1.5% GPL volume fraction. Most interestingly, novel toughening mechanisms were observed that show GPL wrapping and anchoring themselves around individual ceramic grains to resist sheet pullout. The resulting cage-like graphene structures that encapsulate the individual grains were observed to deflect propagating cracks in not just two but three dimensions.