Corrosion resistance of HVOF-sprayed Ni2Si intermetallic coatings in hot H2SO4 medium

Corrosion behavior of high velocity oxy-fuel (HVOF) Ni2Si intermetallic coatings was investigated by means of Tafel polarization tests and electrochemical impedance spectroscopy (EIS) measurements in 70% H2SO4 solutions at 75 °C. Mott-Schottky analysis was also carried out to investigate semiconductive properties of passive films. It was found that the corrosion rate of HVOF Ni2Si coating was much lower than that of stainless steel substrate. Both Ni2Si bulk and coating materials showed an active-passive behavior with a wide passive range during anodic polarization. EIS measurements at open circuit conditions revealed that the system showed one time constant at low frequencies which was attributed to charge transfer processes. Under passive conditions, one time constant was observed at high frequencies which was related to formation of passive films. Further investigation showed that passive film formed on Ni2Si materials in H2SO4 is a p-type semiconductor with acceptor density in the order of 1020 cm− 3.