Beneficial effects of CeO2 addition on microstructure and corrosion behavior of electrodeposited Ni nanocrystalline coatings

This paper presents an experimental study of the effects of CeO2 addition on the microstructure and corrosion behavior of nanocrystalline Ni coatings. A novel method of ultrasound-assisted pulsed electrodeposition was used to prepare the coatings from a modified Watts-nickel electrolyte. Surface morphologies and micro-structural evolution of the coatings before and after aging treatments were characterized using E-SEM and TEM observations. Furthermore, electrochemical techniques attached with the XRD and XPS analysis were applied to study their corrosion behavior in a 5 wt.% HCl aqueous solution. The underlying mechanisms of corrosion inhibition resulted from the Ce-rich passive layer were discussed in detail. Experimental results indicated that the existence of well-distributed CeO2 phase in the coatings promoted dispersion strengthening through a proper aging treatment at 650 °C for 4 h, thereby achieving an effective bonding link between interfacial boundaries for denser microstructure. According to the measured results from polarization curves and the AC-impedance measurements, it exhibited superior corrosion resistance of the Ni-CeO2 coatings as compared to pure nickel. During the long-term static immersion tests in an acid 5 wt.% HCl aqueous solution, a small amount of Ce3 +/4 + ions was released from the dissolution–precipitation of a Ce-rich phase and served as the corrosion inhibitors. Furthermore, some insoluble corrosion products resulted from the process of electrochemical reactions were favorable for precluding the corroded surface from the corrosive attack and diffusion behavior by Cl− ions.