Characterization of hot-pressed graphene reinforced ZrB₂-SiC composite

In this paper, the hot pressing of monolithic ZrB₂ ceramic (Z), ZrB₂-25vol% SiC composite (ZS), as well as 5wt% graphene reinforced ZrB₂-25vol% SiC composite (ZSG) is investigated. The hot pressing at 1850°C for 60min under a uniaxial pressure of 20MPa resulted in a near fully-dense ZSG composite (>99% relative density). In addition, the influence of graphene reinforcement on the sintering process, microstructure, and mechanical properties (Vickers hardness and fracture toughness) of ZrB₂-SiC composite is discussed. It was disclosed that the grain growth of the ZrB₂ matrix was effectively stopped by SiC particles and graphene nano-platelets. The fracture toughness of ZSG composite (6.4MPam^1/2) was strongly enhanced by incorporating the mentioned reinforcements into the ZrB₂ matrix, which is higher than that of Z ceramic (1.8MPam^1/2) and ZS composite (4.3MPam^1/2). After the hot pressing process, the fractographical outcomes revealed that some graphene nano-platelets were kept in the composite microstructure, apart from SiC grains, which lead to the toughening of the composite through graphene nano-platelets wrapping and pull out, crack deflection, and crack bridging.