Tribological Behaviour of Electroless Ni–P Coatings in Brine Solution and Optimization of Coating Parameters Using Taguchi Based Grey Relation Analysis

Abstract

The present paper deals with the synthesis of electroless nickel–phosphorous (Ni–P) coatings on mild steel substrate and optimization of the coating process parameters for minimum friction and wear in brine solution using Taguchi based grey relation analysis. The study is carried out using different combinations of four coating process parameters, namely, concentration of nickel source (A), concentration reducing agent (B), bath temperature (C) and annealing temperature (D) with three levels each (1, 2 and 3). The wear and friction tests are conducted with a pin-on-disk Wear & Friction Monitor. Taguchi based grey relational analysis is employed for the optimization of this multiple response problem using an L27 orthogonal array. The optimal combination of parameters is found as A3B3C1D2 which yields an improvement in grey grade of 62 % compared to the mean grey grade. ANOVA is performed to find out the significance of the coating parameters and their interactions. Bath temperature and annealing temperature are most influential in controlling friction and wear behavior. The surface morphology and composition of coatings are studied with the help of scanning electron microscopy (SEM), energy dispersed X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. It is found that Ni–P coating is amorphous (weight percentages: 91.56 % Ni and 8.44 % P) in as-deposited condition but gradually turns crystalline with heat treatment. The worn surface morphology reveals abrasive wear mechanism.