Densification and tribological profile of niobium oxide

• Nb2O5 free of micro-cracks (monoclinic Nb12O29 or NbO2.416) can be obtained.
• Nb2O5 determines the frictional behavior and contributes to wear protection of NbC.
• Nb2O5 determines the load carrying capacity of NbC.
• At high sliding speeds, the wear rates of reduced Nb12O29 are close to NbC.
• Polymorphs of Nb2O5 are formed by tribo-oxidation on NbC.

The origin of the intrinsic wear resistance of NbC-based materials is investigated through an assessment of the tribological performance of fully dense, crack-free spark plasma sintered Nb2O5 (here as a reduced polymorph: monoclinic Nb12O29 or NbO2.416). The most likely wear mechanism on NbC is the tribo-oxidation to Nb2O5. The unlubricated (dry) friction and wear behavior of alumina (99.7%) mated against rotating disks of crack-free niobium(V)oxide (Nb2O5) under unidirectional sliding (0.03–10 m/s; 22 °C and 400 °C) and oscillation (f=20 Hz, dx=200 mm, 2/50/98% rel. humidity, n=105/106 cycles) will be presented. The microstructure and mechanical properties of the crack-free Nb2O5 are assessed. The tribological data obtained are benchmarked with different NbC grades, ceramics, cermets and thermally sprayed coatings.