Environmentally friendly NbC-Fe-based coatings for wear and corrosion protection

NbC-based cermets, as an alternative to the predominant WC-Co-based systems, have great potential to meet the demand for wear-resistant coatings with less impact on the environment and human health. Compared to WC, NbC benefits from a significantly lower density and, thanks to its good wettability, enables environmentally friendly Fe-based alloys to be used as a matrix replacing carcinogenic cobalt. In this work, various experimental NbC-Fe-based powder materials were developed by agglomeration and sintering and processed using high-velocity flame spraying. The coatings were analyzed regarding their microstructure, hardness and their properties in terms of wear and corrosion. Tribological tests were performed in accordance to ASTM G99 (“Pin-on-Disk”) and ASTM G65 (“Dry Sand/Rubber Wheel”) and additionally oscillating dry sliding wear resistance at room temperature and elevated temperatures up to 800°C. The corrosion properties were investigated based on polarization curves with 3.5% NaCl as well as immersion in 1 N H2SO4, 1 N NaCl and water. The properties were benchmarked against the state-of-the-art coating systems WC-CoCr and Cr3C2-NiCr. The results show, that the novel systems are comparable or partially outperforming the existing benchmarks, promising a future for environmentally friendly NbC-Fe-based coatings.