Design, fabrication and mechanical properties of multidimensional graded ceramic tool materials

A type of multidimensional graded ceramic tool materials (MGTMs) was designed and fabricated by vacuum hot-pressing sintering technology. The microstructure and compositional distribution of tool simultaneously changed in two different directions. The tool-chip and tool-workpiece contact regions were designed to have high hardness, and metal phases Mo and Ni were added to produce a gradual increase in toughness from the outer layer to core layer. The effect of orientation angle, thickness ratio and sintering parameters on the mechanical properties and microstructure were investigated. The experimental results showed that the composites, sintered at 1700 °C for 15 min, with the orientation angle of 30° and a thickness ratio of 0.4, had the optimal comprehensive mechanical properties. In addition, the crack propagation paths were observed to analyze the toughening mechanisms for the multidimensional graded ceramic tool materials. It was found that there is a crack resistance behavior when the crack extended from the outer layer to transition layer. The effect of the angle between the crack and graded interface on crack propagation paths was also investigated and the results indicated that the small angle was favorable for the crack deflection when the cracks passed through the graded interface. The residual thermal stress contributed to the occurrence of the crack bridging and transgranular fracture inside the Al2O3 grains, while the intergranular fracture and crack deflection were observed around the TiC grains.