| Abstract: | NiCrBSi alloy powders were sprayed on a low carbon steel substrate using High velocity oxy-fuel (HVOF) spraying technique and then the samples with coating were heat treated in air furnace for 2h or 10min at 900°C. The corrosion failure process and corrosion resistance of coatings in 3.5% NaCl aqueous solution were investigated by using Electrochemical Impedance Spectroscope (EIS). EIS data shows that the as-sprayed coating cannot resist the penetration of corrosive solution and after 20h the steel substrate begins to be corroded. Local corrosion happens in 2h heat-treated coating if contacting coating with brine longer than 15h, while shape of EIS plots can hold stable for a long time and uniform corrosion happens in 10min heat-treated coating. Relationship of corrosion resistance with time for as-sprayed coating and heat-treated coatings in 3.5% NaCl was obtained using equivalent circuits. The corrosion resistance of 10min heat-treated coating and resistance to penetration of aqueous medium are far better than of as-sprayed coating, but the corrosion resistance of heat-treated coatings with long holding time (2h) is inferior to that of as-sprayed coating. The reasons why heat treatment can change the corrosion behavior of sprayed coating were discussed by the aid of analyzing microstructure. |
