Influence of VC and Mo2C on the microstructure and mechanical properties of Ni bonded NbC-cermets

The current study reports on the effect of VC and Mo2C carbides on the microstructure and mechanical properties of Ni bonded NbC cermets. NbC-Ni-metal carbide powder mixtures were liquid phase sintered for 1 h at 1420°C in vacuum. Two-phase cermets composed of a cubic NbC matrix and an evenly distributed fcc Ni binder were obtained. The NbC grain growth was significantly inhibited and a homogeneous NbC grain size distribution was obtained in the cermets with VC and/or Mo2C additions. The mechanical properties of the NbC-Ni matrix cermets are dependent on the carbide and Ni binder content. The liquid phase sintered NbC-12 vol% Ni cermet had a modest Vickers hardness (HV30) of 1117 ± 22 kg/mm2 and an indentation toughness of 9.1 ± 0.5 MPa m1/2. With the addition of 10-15 vol% VC, the hardness increased to 1399 ± 15 kg/mm2, whereas the toughness increased to 11.3 ± 0.1 MPa m1/2. Addition of 10 vol% Mo2C into a NbC-12 vol% Ni mixture led to a HV30 hardness of 1397 ± 21 kg/mm2 in combination with a fracture toughness of 9.9 ± 0.2 MPa m1/2. A maximum flexural strength of 1899±77 MPa was obtained in the cermet with 20 vol% Ni binder and 4 vol% VC + 4 vol% Mo2C addition, exhibiting a high indentation fracture toughness of 15.0 ± 0.5 MPa m1/2.