Microstructure and mechanical properties of NbC matrix cermets using Ni containing metal binder

The current study reports on the effect of the addition of Al metal and secondary refractory carbides on the microstructure and mechanical properties of Ni bonded NbC matrix cermets. Powder mixtures were pressurelessly sintered for 1 h at 1420°C in vacuum. Microstructural and elemental mapping of the sintered cermets were performed by electron probe microanalysis (EPMA) to reveal the effect of the additions on the NbC grain morphology, grain growth and binder composition. Results indicated that NbC grain growth was suppressed and a homogeneous NbC grain size distribution was obtained in the cermets with the addition of Al and secondary carbides, i.e. Mo2C + VC + WC, as compared to the pure Ni binder. The liquid phase sintered NbC-12 vol% Ni cermet had a Vickers hardness (HV10) of 1130 ± 22 kg/mm2 and indentation toughness of 11.8 ± 0.4 MPa m1/2. With the addition of 4 vol% WC-4 vol% VC-4 vol% Mo2C, the hardness increased to 1490 ± 15 kg/mm2, whereas the corresponding toughness decreased to 9.2 ± 0.4 MPa m1/2. Addition of 4 vol% Mo2C into WC-13.8 vol% Ni-52.3 vol% NbC mixture further increased the hardness to 1620 ± 19 kg/mm2 in combination with a moderate fracture toughness of 7.7 ± 0.2 MPa m1/2.