Microstructure and Mechanical Properties of TiB2-HfC Ceramic Tool Materials

Abstract

Effects of different metallic additives and sintering parameters on microstructure and mechanical properties of TiB2-HfC ceramics were investigated. The results showed that the core-rim structure and HfC particle dispersion were discovered in these ceramics. Only Co as the metallic additive could more easily promote the formation of the strip-shaped TiB2 than the others; TiB2-HfC-Ni-Mo ceramic had more serious agglomeration of HfC particles than the others; for TiB2-HfC ceramic, using Ni-Co as the metallic additive could obtain better mechanical properties than using the others. In addition, with sintering temperature increasing from 1500°C to 1650°C, grains grew gradually and the core-rim structures became fewer and unobvious. Extending the holding time from 15 min to 60 min, grain size just had a slight increase, and the influence of holding time on mechanical properties was not significant. The increase of sintering temperature (1500–1650°C) could lead to more obvious grain growth and change of core-rim structure than the increase of holding time (15–60 min). The better sintering parameters for TiB2-HfC-Ni-Co ceramic were 1600°C and 30 min. Besides, better mechanical properties of TiB2-HfC-Ni-Co ceramic sintered at 1600°C with 30 min holding time were that Vickers hardness was 21.2 ± 0.3 GPa, flexural strength was 1169 ± 16 MPa, and fracture toughness was 6.7 ± 0.3 MPa m1/2. Meanwhile, its toughening mechanisms included core-rim structure, particle dispersion, crack deflection and crack bridging. The mixed intergranular/transgranular fracture could also improve fracture toughness.