Effects of Mo additions on the corrosion behavior of WC–TiC–Ni hardmetals in acidic solutions

Abstract

The corrosion behavior of WC–TiC–Ni cemented carbides with the additions of molybdenum was investigated in 1M H2SO4 and 1M HCl solutions utilizing potentiodynamic polarization, long-term immersion tests and surface analytical techniques. The results show that the Mo additions can enhance the corrosion resistance of WC–TiC–Ni hardmetals owing to the formation of new (Ti, W, Mo)C phase based on TiC. Pseudopassivity was observed in the polarization curves of WC–Ni and WC–TiC–Ni hardmetals in HCl. However, the additions of molybdenum can make WC–TiC–Ni hardmetals passivated visibly in curves at 600mV–1000mV and enhance the pitting corrosion resistance due to the formation of MoO3 film. In addition, all nickel based alloys show the typical passivation behavior in H2SO4 caused by the formation of NiSO4, NiWO4 and continuous metal oxide films.