Microstructure and fracture toughness of SiAlCN ceramics toughened by SiCw or GNPs

Mechanical alloying and spark plasma sintering (SPS) were used to prepare dense SiAlCN ceramic and SiAlCN ceramic toughened by SiC whiskers (SiCw) or graphene nanoplatelets (GNPs). The influences of different reinforcements on the microstructure and fracture toughness were investigated. The SiAlCN ceramic exhibited a fracture toughness of 4.4 MPa m1/2 and the fracture characteristics of grain bridging, alternative intergranular and transgranular fracture. The fracture toughness of SiCw/SiAlCN ceramic increased to 5.8 MPa m1/2 and toughening mechanisms were crack deflection, SiCw bridging and pull-out. The fracture toughness of GNP/SiAlCN ceramic increased significantly, which was up to 6.6 MPa m1/2. GNPs played an important role in grain refinement, which resulted in the smallest grain size. Multiple toughening mechanisms, including crack deflection, crack branch, GNP bridging and pull-out could be found. The better toughening effect could be attributed to the larger specific surface area of GNPs and the appropriate interface bonding between GNPs and matrix.