A Grey-Fuzzy Based Approach for the Optimization of Corrosion Resistance of Rebars Coated with Ternary Electroless Nickel Coatings

Abstract

Corrosion is an important phenomenon that occurs at concrete-rebar interface and affects the life of structures in coastal environments. Fe-600 grade steel is used in India for construction purposes especially in seismic zones. Hence, the corrosion of the rebars and its optimization is necessary to increase the lifetime of structures. In this regard, the present investigation examines the applicability of electroless Ni-P based ternary coatings as candidates for corrosion protection and obtains an optimal bath formulation. Investigation of electrochemical corrosion phenomenon (potentiodynamic polarization) was carried out in 3.5% NaCl to simulate saline coastal environment. Ni-P coatings with Cu and W inclusion were considered due to their proven corrosion resistance. The bath constituents such as nickel sulphate (Ni source), sodium hypophosphite (reducing agent and source of P) and the tungsten / copper concentration were varied to get various elemental composition following a sequential experimental design i.e. Taguchi’s L9 orthogonal array. A grey based fuzzy reasoning approach was proposed to optimize the bath and achieve enhanced corrosion resistance. The optimized coatings exhibited initiation of passivation which could prove to be beneficial for the health of the structure in the long-run. A noble corrosion potential and lower corrosion current density could be obtained in the coated rebars from the grey fuzzy methodology.

Keywords

• ni-w-p
• ni-cu-p
• electroless
• rebar
• grey-fuzzy optimization
• corrosion