Characterizing the Electrochemical Corrosion Behaviour of a Ni- 28wt.%Al Composite Coating in 3.5% NaCl Solution

The electrochemical corrosion behaviour of an electrodeposited Ni-28wt.%Al composite coating was characterized after 24 h and 72 h immersion periods in 3.5% NaCl solution, using electrochemical and surface probe techniques. Open circuit potential (OCP) and potentiodynamic polarization revealed that the Al particles modify the electrochemical corrosion behaviour of the Ni coating by shifting its EOCP more negatively and increasing its anodic dissolution current density, after 24 h immersion in 3.5% NaCl solution. Compared with the Ni coating, the composite can exhibit well-reduced anodic current density and slightly increased cathodic current with immersion up to 72 h. XPS characterization showed that a high rate of water adsorption and rapid formation of a continuous Ni(OH)(2) initially occurs on the composite surface which, however, readily thickens during prolonged immersion time and promotes the corrosion product enrichment with Al2O3. This greatly decreased the rate of corrosion and susceptibility to pitting for the Ni-28wt.%Al composite after 72 h immersion in 3.5% NaCl solution.