Development of NbC-based hardmetal coatings

Niobium carbide (NbC) can be an alternative to WC in hardmetal coatings. NbC has long been employed to produce bulk hardmetals, e.g. for cutting tools, but it has not been investigated in coatings.

In this contribution, we provide an overview of our research with NbC-based coatings having Ni- and Fe-based matrices. Searching a suitable binder that provides good performance with relatively low cost is one of the challenges. The feedstock materials were prepared by High-Energy Ball Milling (HEBM) due to the flexibility and scalability of this process, which yields quite rounded particles containing a uniform distribution of fine NbC grains. The coatings were obtained by H₂-fuelled High Velocity Oxygen-Fuel (HVOF) and High Velocity Air-Fuel (HVAF) spraying.

NbC-NiCr formulations, especially with 40 vol.% matrix, exhibit a good combination of room-temperature and intermediate-temperature sliding wear resistance, tested by the ball-on-disc method, and excellent corrosion resistance in aqueous 3.5% NaCl. NbC-40vol.%FeCrMo is more brittle and less sliding wear-resistant at room temperature, but it exhibits excellent wear resistance at 400 – 500 °C due to the formation of a protective tribo-oxidized “glaze”. Optimization of the metal matrix of powder is still ongoing, towards the achievement of more homogeneous distribution of constituents (Fe, Cr, Mo).