Microstructure and mechanical properties of TiC0.7N0.3-HfC cermet tool materials

TiC0.7N0.3-HfC cermet tool materials were fabricated by hot-press sintering. Effects of different metal additives (Ni, Co, Ni-Co and Ni-Mo), sintering temperature and holding time on the microstructures and mechanical properties of TiC0.7N0.3-HfC cermets were investigated. Results showed that Ni-Mo or Ni-Co as metal additives was better for the mechanical properties of TiC0.7N0.3-HfC cermets than only Ni or only Co as the metal additives and Ni-Mo better than Ni-Co. HfC particle dispersion existed in these four cermets and only in the TiC0.7N0.3-HfC-Ni-Mo cermet the core-rim structure obviously existed. TiC0.7N0.3-HfC-Ni-Mo cermet had significantly smaller grains than the other three cermets because Ni-Mo can significantly refine the grain. With the sintering temperature increasing from 1450 °C to 1650 °C, grains grew gradually; Vickers hardness and flexural strength decreased gradually and the fracture toughness increased firstly and then decreased. With the holding time increasing from 15 min to 60 min, grains grew gradually; Vickers hardness, flexural strength and the fracture toughness increased firstly and then decreased. TiC0.7N0.3-HfC-Ni-Mo cermets sintered at 1450 °C with 30 min holding time had the better comprehensive mechanical properties with flexural strength of 1346.41 ± 31 MPa, fracture toughness of 8.46 ± 0.23 MPa m1/2 and Vickers hardness of 22.91 ± 0.22 GPa.