Influence of in situ crystallisation on tribological and corrosion properties of Fe-based amorphous coatings synthesised by high velocity oxyfuel spraying

This current study emphasises understanding the influence of the coating thickness and powder feed rate on microstructural evolution and their subsequent effects on electrochemical and wear behaviour of the Fe-based amorphous/nanocrystalline composite coating (Fe57Cr9Mo5B16C7P6, at. %) synthesised via high velocity oxy fuel (HVOF) spraying. Microstructural analysis revealed that with an increase in the coating thickness, porosity content decreased with improved intersplat bonding; whereas the amorphous phase fraction reduced. Regardless, with an increase in the powder feed rate in both low and high thickness coatings, amorphicity increased with reduced porosity content, resulting in dense coating microstructure. Both micro and nanohardness increased with an increase in coating thickness due to a higher proportion of crystalline phase fraction and low porosity content whereas an increase in overall hardness with an increase in powder feed rate is attributed to low porosity content in the coatings. Wear test in the coating with high thickness (400 ± 20 µm) and high powder feed rate (60 g·min−1) exhibited superior wear resistance. This was attributed to a low porosity fraction and a high proportion of intermetallic phases. Potentiodynamic polarisation test performed in 3.5% NaCl solution showed that coating with high thickness (400 ± 20 µm) and high powder feed rate (60 g·min−1) exhibits superior corrosion resistance attributing to dominance of the optimum level of reduced porosity content over amorphous phase fraction.