The effects of HfB₂ and HfN additions on the microstructures and mechanical properties of TiB₂-based ceramic tool materials were investigated. The results showed that the HfB₂ additive not only can inhibit the TiB₂ grain growth but can also change the morphology of some TiB₂ grains from bigger polygons to smaller polygons or longer ovals that are advantageous for forming a relatively fine microstructure, and that the HfN additive had a tendency toward agglomeration. The improvement of flexural strength and Vickers hardness of the TiB₂-HfB₂ ceramics was due to the relatively fine microstructure; the decrease of fracture toughness was ascribed to the formation of a weaker grain boundary strength due to the brittle rim phase and the poor wettability between HfB₂ and Ni. The decrease of the flexural strength and Vickers hardness of the TiB₂-HfN ceramics was due to the increase of defects such as TiB₂ coarse grains and HfN agglomeration; the enhancement of fracture toughness was mainly attributed to the decrease of the pore number and the increase of the rim phase and TiB₂ coarse grains. The toughening mechanisms of TiB₂-HfB₂ ceramics mainly included crack bridging and transgranular fracture, while the toughening mechanisms of TiB₂-HfN ceramics mainly included crack deflection, crack bridging, transgranular fracture, and the core-rim structure.

TiC_0.7N_0.3-HfC-WC-Ni-Mo cermet tool materials were fabricated by hot pressing technology at 1450 °C. The effects of WC (tungsten carbide) content on the microstructure and mechanical properties of TiC_0.7N_0.3-HfC-WC-Ni-Mo cermet tool materials were investigated. The results showed that the TiC_0.7N_0.3-HfC-WC-Ni-Mo cermets were mainly composed of TiC_0.7N_0.3, Ni, and (Ti, Hf, W, Mo)(C, N); there were three phases: a dark phase, a gray phase, and a light gray phase. The dark phase was the undissolved TiC_0.7N_0.3, the gray phase was the solid solution (Ti, Hf, W, Mo)(C, N) poor in Hf, W, and Mo, and the light gray phase was the solid solution (Ti, Hf, W, Mo)(C, N) rich in Hf, W, and Mo. The increase of WC content could promote the process of HfC to form a solid solution and the HfC formed a solid solution more easily with WC than with TiCN. The increase of the solid solution made the microstructure more uniform and the mechanical properties better. In addition, the Vickers hardness, flexural strength, and fracture toughness of the TiC_0.7N_0.3-HfC-WC-Ni-Mo cermet increased with the increase of WC content. When the content of WC was 32 wt %, the cermet obtained the optimal comprehensive mechanical properties in this investigation. The toughening mechanism of TiC_0.7N_0.3-HfC-WC-Ni-Mo cermet tool materials included solid solution toughening, particle dispersion toughening, crack bridging, and crack deflection.