Corrosion performance of steel rebars by application of electroless Ni-P-W coating: An optimization approach using grey relational analysis

Electroless deposited Ni-P-W coatings were investigated as a potential candidate for corrosion prevention of steel rebars subjected to chloride environment. Potentiodynamic polarization was utilized to test corrosion resistance of bare and coated rebars. Taguchi based grey relational analysis was used to predict a bath composition that would result in enhanced corrosion resistance of the coated rebars. Higher corrosion potential (-258 mV) and low corrosion current density (0.065 mA/cm2) could be achieved compared to bare rebars (-653 mV, 11.7 mA/cm2) for a nickel sulphate concentration of 30 g/l, sodium hypophosphite concentration of 17 g/l and sodium tungstate concentration of 20 g/l in the coating bath. The morphology of the bare and coated rebars post corrosion revealed severe cracking of the bare rebars. While the Ni-P-W coated rebar at optimal bath combination predicted by Taguchi method suffered negligible damage in chloride environment with the onset of an oxide layer.