Journal of Minerals & Materials Characterization & Engineering , Vol. 10, No.14, pp.1307-1327, 2011 jmmce.org Printed in the USA. All rights reserved 1307 Study of Potentiodynamic Polarization Behaviour of Electroless Ni-B Coatings and Optimization using Taguchi Method and Grey Relational Analysis Suman Kalyan Das and Prasanta Sahoo* Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India *Corresponding author: psahoo@mech.jdvu.ac.in , psjume@gmail.com ) ABSTRACT Electroless nickel coatings are very popular for their corrosion resistant actions. The present article attempts to study the corrosion behaviour of electroless Ni-B coatings by varying the coating parameters viz. bath temperature, reducing agent concentration and nickel source concentration together with the annealing temperature. The electrochemical parameters viz., corrosion potential and corrosion current density are evaluated with the help of potentiodynamic polarization experimentation. Taguchi based Grey analysis is employed in order to optimize this multiple response problem and the optimal combination of parameters for maximum corrosion resistance for Ni-B coatings is presented. Moreover, analysis of variance reveals that bath temperature and concentration of nickel source have significant influence on the corrosion performance of the coating. The microstructure characterization of the coating is also conducted with the help of scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis. The Ni-B coating in general exhibits a nodular structure and turns crystalline with heat treatment. The corroded surface exhibits cracks and black spots which imply the occurrence of localized corrosion. Keywords: Electroless coatings, Ni-B, Corrosion, Grey Taguchi. 1. INTRODUCTION Electroless nickel coatings have received wide acceptance by the industrialists as well as the research community due to their ability to provide hardness, wear resistance, corrosion resistance and low friction coefficient [1, 2]. Moreover, the coating could be engineered to suit the need for a particular application. The properties of electroless nickel coatings are greatly affected by the type of reducing agent present in the bath. Hypophosphite reduced (Ni-P) electroless nickel coatings have already proved their mettle as a coating for tribological based applications [3-5] and attention has shifted towards borohydride reduced (Ni-B) coatings [5-12] as the latter can provide improved properties. Electroless Ni-B coatings are widely used in aerospace and automotive industries particularly due to their high hardness and hence splendid wear resistance [1]. Ni-B coatings are found to be harder than Ni-P coatings in as deposited phase [6]. With heat treatment, the hardness of Ni-B coating is found to increase even more [6, 7]. The increase of hardness of Ni-B coating with heat treatment is generally attributed to the modification of deposit structure allowing the