Highly strain tolerant and tough ceramic composite by incorporation of graphene

Graphene is an ultra-thin, remarkably flexible and highly stiff 2D material that can profoundly change the microstructure of composite as filler phase, giving rise to mechanical properties greatly different from traditional composites. However, there are very few examples that demonstrate the exceptional properties in graphene based ceramic composite because of the tradeoff between small thickness of graphene platelet and dispersion uniformity in processing. Here, a fully dense Al₂O₃ composite with uniformly dispersed few-layer graphene (FLG) is prepared by heteroaggregation technique and spark plasma sintering. It is found that in comparison to monolithic Al₂O₃, drastically reduced Young's modulus (298 GPa), completely retained fracture strength (417 MPa) and enhanced fracture toughness (5.3 MPa m^1/2) are simultaneously realized in this composite, leading to an unprecedented increase of strain tolerance by ∼40% at merely 2.18 vol.% of filler loading. It is believed that the unique highly wrinkled structure of FLG at triple junctions of ceramic matrix causes the inefficient load transfer before crack initiation and thus low stiffness in composite. Whereas after crack initiation, by the "stretched filler bridging" of FLG platelet behind crack tip, the toughness of composite is enhanced so that the high fracture strength can be retained.