Microstructures and mechanical properties of functionally graded TiCN–TaC ceramics prepared by a novel layer processing strategy

Functionally graded TiCN–TaC ceramics (FGTTCs) were fabricated using a novel layer processing method based on a vacuum hot-press sintering technology. Microstructural investigations revealed a visibly layered structure for the FGTTCs with relatively flat boundaries between the neighboring layers; additionally, the layer thickness was facilely controlled. With an increase in the sintering temperature, the hardness and flexural strength of the surface and middle layers of the FGTTCs initially increased, and then decreased. The fracture toughness of the surface layer did not undergo significant changes after sintering at various temperatures, except at 1500 °C. The FGTTC sintered at 1350 °C contained uniform fine grains and simultaneously exhibited transgranular and intergranular fracture modes. Further, it presented excellent comprehensive mechanical properties, i.e., surface layer hardness = 20.28 ± 0.18 GPa, flexural strength = 1553.76 ± 22 MPa, surface layer fracture toughness = 7.29 ± 0.24 MPa m^1/2. Under the same sintering conditions, our FGTTCs presented superior mechanical properties against homogeneous TiCN–TaC ceramics (HTTCs), achieving a considerably higher flexural strength (1553.76 ± 22 vs 953.35 ± 24 MPa).