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.