In the present work, Inconel-625 cladding was performed on a mild steel (MS) substrate through a cost-effective microwave technique. Cladding was performed in an industrial microwave oven operated at 1.2 kW and 2.45 GHz. The XRD observation indicates the presence of Laves and carbide phases in addition to a Ni-Cr-Fe based face-centered-cubic (fcc) matrix in the fusion zone microstructure of the clad specimen. The microstructural characterization shows a homogenous and dense microstructure with a porosity value of less than 1%. The columnar dendrites grew perpendicularly to the substrate was observed in the clad zone microstructure. The average microhardness of the deposited clad was significantly higher than that of the base metal (MS), indicating improved surface properties of the base material. Further, corrosion testing indicates that the clad specimen has significantly higher corrosion resistance than that of the base metal (MS) in a 3.5 wt% NaCl solution.

In the present research work, microstructural evolution and corrosion behaviour of the high-velocity oxy-fuel (HVOF) sprayed Alloy718-nano Al ₂ O ₃ composite coatings were examined. These coatings were deposited on the grey cast iron (C.I) substrate. The agglomerated nano-Al ₂ O ₃ reinforcement particles in three different proportions (10, 20 & 30 wt.%) were varied in the Alloy718 based matrix to develop the composite coatings. Corrosion testing of bare and coated samples was carried out at an ambient temperature in the NaCl solution (3.5 wt.%) using the potentiodynamic polarization technique. The polarization resistance (Rp), the corrosion efficiency and the corrosion rate (CR) were measured for the developed coatings and substrate. The surface morphology of as-sprayed and corroded coatings was studied using scanning electron microscopy coupled with energy-dispersive spectroscopy. X-ray diffraction analysis was conducted to determine the different phases present in the feedstock powders and as-sprayed coatings. The as-sprayed coatings were seen with nano-Al ₂ O ₃ particles uniformly embedded in the melted Alloy718 matrix. The coating with 30 wt.% nano-Al ₂ O ₃ particles revealed the maximum microhardness of about 1296 ± 21 HV _0.2 compared to other coatings. The results showed that the corrosion resistance of the composite coatings increases with the increase in alumina particles in the Alloy718 matrix. The 30 wt.% alumina coating showed maximum resistance to corrosion due to the maximum decrease in the electrochemically active area associated with this coating.