Composite (glass + crystalline) coatings from blast furnace pig iron by high velocity oxy-fuel (HVOF) process and their electrochemical behavior

By Sarkar, Kuntal; Rai, P. K.; Katiyar, Prvan Kumar; Satapathy, Biswajeet; Pathak, Abhishek Subhash; Dutta, Monojit; Banerjee, Atanu; Mondal, K.
Published in Surface and Coatings Technology 2019

Abstract

The present study is the first report on the possibility of blast furnace (BF) pig iron-based corrosion resistant and very hard composite (glass + crystalline) coating on a mild steel. The BF metal is of very lean and cheap alloy chemistry and its coating on the mild steel has been found to show similar corrosion resistance as shown by the stainless steel (SS) coating on the mild steel. The BF coating has been made through high velocity oxygen fuel (HVOF) thermal spray process at different powder feed rates of 30, 40, 50 and 60 g/min. The microstructural characterization of coatings reveals good inter-splat bonding with low porosity in the range of 3 to 5%. The corrosion potential of the BF coatings is significantly negative than that of the mild steel substrate as well as the SS coating suggesting that the BF coatings could provide sacrificial protection to the mild steel substrate in addition to the comparable corrosion resistance as shown by the SS coating in freely aerated 3.5% NaCl solution. It has been found that the corrosion resistance of these BF coatings is significantly higher than the conventional galvanized coating, allowing them to be a promising and better sacrificial coatings than the galvanized one. The high corrosion resistance of the BF coatings could be attributed to its partially amorphous structure, presence of high C, Si and P, and relative portion of the insoluble ?-FeOOH phase compared to the soluble ?-FeOOH phase in the rust, indicated protection parameter of the rust (?/?*).

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