Microstructure and toughening mechanisms of Al2O3/(W, Ti)C/graphene composite ceramic tool material

To toughen the Al2O3 matrix ceramic materials, Al2O3/(W, Ti)C/graphene multi-phase composite ceramic materials were fabricated via hot pressing. The effects of the graphene nanoplates (GNPs) content on microstructure and mechanical properties were investigated. Results showed that the fracture toughness and flexural strength of the composite added with just 0.2 wt% GNPs were markedly improved by about 35.3% (~ 7.78 MPa m1/2) and 49% (~ 608.54 MPa) respectively compared with the specimens without GNPs while the hardness was kept about 24.22 GPa. However, the mechanical properties degrade with the further increase of GNPs' content owing to the increased defects caused by agglomeration of GNPs. Synergistic toughening effects of (W, Ti)C and GNPs played an essential role in improving the fracture toughness of composites. By analyzing the microstructures of fractured surface and indentation cracks, besides GNPs pull-out, crack deflection, crack bridging, crack branching and crack arrest, new toughening mechanisms such as break of GNPs and crack guiding were also identified. Furthermore, interface stress can be controlled by means of stagger distributed strong and weak bonding interfaces correlated with the distribution of GNPs.