Non-wetting behaviour of tungsten carbide powders in nickel weld pool: new loss mechanism in GMAW overlays

This paper presents a new mechanism, observed directly for the first time, to explain low carbide fractions in Ni-WC overlays produced with GMAW. In this loss mechanism, a significant amount of powder loss is a consequence of the non-wetting behaviour of tungsten carbide. High speed videography and quantitative metallography of weld deposits are used to identify this mechanism. The non-wetting mechanism found acts simultaneously with the carbide dissolution mechanism, which until now was the only suggested cause of low carbide fraction in GMAW Ni-WC overlays. The non-wetting behaviour is observed in both short circuit and free flight metal transfer, accounting for carbide losses between 20 and 70% in the experiments performed. Low carbide fraction has prevented the mainstream use of GMAW for Ni-WC overlays, despite the advantages of simplicity, capability of in situ repair, and low capital costs. The findings presented here have a potential large impact for further consumable and process development.