Effect of layer thickness ratio on microstructure and mechanical propertiees of TiC-WC/TiC-TiN laminated ceramics

The TW/TT layered ceramics with five different layer thickness ratios(2:1、1:1、1:2、1:3 and 1:4, respectively) were prepared by dry pressing and vacuum hot pressing sintering technology with TiC as the matrix phase of each layer, WC and TiN as the additive phases of TiC-WC (TW) layer and TiC-TiN(TT)layer, respectively. The effects of layer thickness ratio on the residual stress, microstructure and mechanical properties were investigated. The results showed that there were residual compressive stresses in the TW layer, and the residual compressive stresses gradually increased with the increase of layer thickness ratio, and conversely, the tensile stresses presented in the TT layer gradually decreased. With the increase of the layer thickness ratio, the hardness and fracture toughness of the TW layer as well as the relative density and flexural strength of the material were first increased and then decreased, whereas the fracture toughness and hardness of the TT layer showed an decreasing trend. When the layer thickness ratio was 1:3, the fracture profile had higher density and fewer defects, and the best mechanical properties were obtained, its flexural strength was (946.01±19.1) MPa; Its hardness and fracture toughness in TW were (16.68±0.17) GPa and (10.19±0.22) MPa?m1/2, respectively; Those in TT were (15.73±0.15) GPa and (7.78±0.26) MPa?m1/2, respectively. It was also observed that the average grain size of the TT layer was significantly smaller than that of the TW layer. Crack deflection and crack bridging occured when the crack crossed the layer junction, and the fracture mode was dominated by transgranular fracture and intergranular fracture.