Characterization of hot-pressed graphene reinforced ZrB2-SiC composite

In this paper, the hot pressing of monolithic ZrB2 ceramic (Z), ZrB2-25 vol% SiC composite (ZS), as well as 5 wt% graphene reinforced ZrB2-25 vol% SiC composite (ZSG) is investigated. The hot pressing at 1850 °C for 60 min under a uniaxial pressure of 20 MPa 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 (6.4 MPa m1/2) was strongly enhanced by incorporating the mentioned reinforcements into the ZrB2 matrix, which is higher than that of Z ceramic (1.8 MPa m1/2) and ZS composite (4.3 MPa m1/2). 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.