SEM and hot corrosion evaluation of 80Ni-20Cr coating applying electrochemical techniques

The corrosion resistance of 80 wt. % Ni-20Cr coating applied by the powder flame thermal spray technique on AISI 304 stainless steel has been evaluated in 80 mol % Na₂SO₄-20V₂O₅molten salt using electrochemical techniques. The testing temperatures were 700, 800 and 900°C, and the electrochemical techniques included potentiodynamic polarization curves (PPC) and electrochemical noise (EN). The objective of this research was to obtain the corrosion mechanism from the EN technique and polarization curves. The current and potential time series data were analyzed in the time domain. A SEM analysis of the corroded samples demonstrated that at 900°C a mechanism of sulfur penetration into the substrate was the most important corrosive attack. According with the electrochemical results, the 80 wt. % Ni-20Cr coating suffered localized corrosion and mixed corrosion, determining that the major localized corrosion was observed at the higher temperature.