Microstructure analysis and mechanical characterisation of NiWCrBSi coatings produced by flame spraying

This work presents microstructure and mechanical properties of NiWCrBSi coatings produced onto mild steel substrate by oxyacetylene flame spraying, using two different stoichiometries. Coatings were analysed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. Microhardness tests were carried out using a micro-hardness tester operating with Vickers indenter and the load being 3N. Results showed that both coating microstructures were of lamellar/stratified type, containing several inhomogeneities such as unmelted particles and pores. Coatings consisted mainly of a solid solution (Ni, Cr and Fe), containing two different phases of hexagonal structure, namely WC and Ni31Si12. The presence of WC hard particles contributed to the high coating hardness. Oxidizing flame conditions showed a potential interest for tribological applications, because of a reduced porosity and an increased coating hardness.