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- Niobium carbide (21)
- NbC (11)
- Wear (11)
- Cermet (8)
- Friction (8)
- Sintering (7)
- Cobalt (6)
- Hard metal (6)
- Hardness (6)
- Mechanical properties (6)
Organisationseinheit der BAM
In the present work it was shown that the addition of VC or a combination of VC + Ti(C0.7N0.3) was efficient in reducing the NbC grain growth during liquid phase sintering, when compared to NbC-Ni equivalents. A finest NbC grain size of 1.48 µm was obtained in the NbC-15 Ti(C0.7N0.3)-10 Ni-7.5 VC cermet, exhibiting a hardness of 1486 +/- 7 kg/mm2 and a fracture toughness of 8.7 +/- 0.1 MPa m 1/2.
The tribological profile of alumina (99.7%) mated against binder-less niobium carbide (NbC) rotating disks were determined unidirectional sliding tests (0.17.5 m/s; 22 °C and 400 °C) as well as in oscillation tests (f=20 Hz, Δx=0.2 mm, 2/50/98% rel. humidity, n=105/106 cycles) under un-lubricated (dry) conditions. In addition, the microstructure and mechanical properties of NbC were determined as well. The reason for testing hot-pressed NbC was to avoid side effects generated by sintering additives and/or second phases. The tribological data obtained were benchmarked with different ceramics, cermets and thermally sprayed coatings. NbC exhibited low wear rates under dry sliding associated with high load carrying capacity. The tribological profile established revealed a strong position of NbC under tribological considerations and for closed tribo-systems against traditional references, such as WC, Cr3C2, (Ti,Mo)(C,N), etc.
Full densification of Fe, Co and Ni bonded NbC based cermet’s was achieved by pressure less liquid phase sintering in vacuum for one hour at 1420°C. The hardness and toughness of the NbC matrix cermet’s can be mainly tailored by the binder composition and secondary carbide additions. Ni binder based NbC cermet’s allow the combination of high hardness and improved toughness. The addition of lesser amounts of VC/Cr3C2 in a NbC partially substituted WC-Co cemented carbide increased significantly the hardness in combination with a moderate fracture toughness.
Research and development of WC grades is 90 years ahead of niobium carbide-based hard materials, which showed already as light-weight and unexplored material a very high potential for many technical applications, especially for wear protection and machining. NbC evoluted recently from lab scale to pilot scale, especially in areas where established WC-based materials are causing economic, environmental or technical concerns. Benchmark trials of NbC-based hard metals indicated already a favorable performance in machining of steel components.