Studies of the metallurgical and mechanical properties of high velocity oxy-fuel sprayed stellite-6 coatings on Ni- and Fe-based superalloys

High-velocity oxygen-fuel (HVOF) process is one of the most popular thermal spraying technologies and has been widely adopted by many industries due to its flexibility and the superior quality of coatings produced. This paper demonstrates the successful application of Stellite-6 metallic coatings on the Ni- and Fe-based superalloys by HVOF process for hot corrosion applications. The microstructure, porosity, coating thickness, phase formation and microhardness properties of the coatings were characterised using the combined techniques of optical microscopy, X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive analysis (SEM/EDAX) and electron probe microanalysis (EPMA). The coatings exhibited characteristic splatlike, layered morphologies due to the deposition and re-solidification of successive molten or semi-molten powder particles. The coating possesses porosity, unmelted and semimelted particles, and inclusions. The coatings have porosity less than 2% and hardness values in the range of 800–900 Hv. The as sprayed microstructure has a face centred cubic (fcc) Co-rich metallic matrix with very small fraction of CoNiO2 spinel oxide. EDAX analysis of the coating microstructure confirmed that the coating composition is similar to the feedstock powder.