An investigation on cavitation-corrosion behavior of Ni/β-SiC nanocomposite coatings under ultrasonic field.

Ni/β-SiC nanocomposite coating was electroplated on the 17-4 PH SS (precipitation-hardening stainless steel) in modified Watt's bath. The role of cyclic-cavitation (Duty cycle: 50%) on corrosion behavior of Ni/β-SiC nanocomposite coating in 3.5 wt% NaCl solution was investigated using open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results of OCP tests demonstrated that cavitation led to positive shifts in the potential for Ni composite coating, while it caused the potential negative shifts in the case of 17-4 PH SS. The results of the polarization tests under cavitation condition exhibited positive shifts in potential and an increase in current density up to a specific anodic potential. In higher anodic potentials, the cavitation had a reverse effect on potential and current density. Moreover, it increased the overall corrosion current density. EIS measurements illustrated a severe reduction in electrochemical resistance of both 17-4 PH SS (from 228.15 kΩ.cm2 to 14.85 kΩ.cm2) and Ni composite coating (from 20.19 kΩ.cm2 to 5.00 kΩ.cm2) after 20 h of the cavitation tests. The cumulative mass loss measurements showed that the mass loss for the substrate (10.3 mg.cm-2) was about five times more than that of Ni composite coating (2.3 mg.cm-2). Also, in the coated specimen, the incubation time is increased and the growth slop of the accelerating period decreased under cavitation condition.