Microstructure of Ni-Cr-Based Coating for Corrosive Conditions

The present study was done to investigate the microstructure and erosion–corrosion behavior of Inconel 625 coating. 270 µm thick coating was successfully deposited on alloy-76 with cold spray coating process, and from microstructure analysis, it is found that coating is dense, smooth and hard with porosity less than 1%. Surface porosity was further reduced to less than 0.5% by burnishing process. Corrosive tests were performed in the actual working plant of medical waste incinerator for 10 cycles of total 1000 h at 900 °C. Coated samples performed better as compared to bare alloy mainly because of formation of chromia-rich protective surface scale layer which had resisted the penetration of corrosive species toward the substrate. Erosion–corrosion rates in mils per year (mpy) are 108.29, 43.45 and 30.69 for bare alloy-76, Inconel 625 coated and burnished-625 coated alloy-76, respectively. Active oxidation mechanism has been noticed in case of bare alloy in corrosive incinerator environment. Cold spray coated Inconel 625 microstructure is suitable for application in erosive–corrosive high temperature environment.