Electrochemical Impedance Spectroscopy of Ni-B Coatings and Optimization by Taguchi Method and Grey Relational Analysis

Abstract

Electroless nickel coatings possess several advantages over electroplating such as ability to coat any material and with uniform thickness. Besides, these coatings are used mainly for their wear resistance and corrosion resistance applications. The present study addresses the corrosion behavior of the coating based on electrical impedance spectroscopy. The effect of the four parameters viz. bath temperature, reducing agent concentration, nickel source concentration and annealing temperature, on the electrochemical characteristics (charge transfer resistance and double layer capacitance) are studied with the help of Taguchi method and grey relational analysis. It is found that the bath temperature has the most significant influence on the corrosion behavior of the coating followed by nickel source concentration. The microstructural characterization of the coating is done with the help of scanning electron microscope, X-ray diffraction analysis and energy dispersive X-ray analysis.

Recent advances in electroless nickel‑boron coatings

“…This is usually linked with the columnar morphology of EN-B that is not as favorable as the lamellar one of EN-P. Some EN-P coatings have high corrosion resistance in acid media due to high phosphorus content in the deposits that lead to the formation of a hypophosphite thin film at the surface, which increases the corrosion resistance [28,20,25]. In all cases, electroless coatings have better behavior than similar electroplated deposits [16,22].…”

“…One of the most attractive properties of EN coatings is their hardness that is higher than that of electroplated deposits [27]. Among electroless nickel coatings, nickel-boron (EN-B) coatings present by far the highest hardness [28], with values as high as 872 hv 100 reported for EN-B deposits with 8 wt% B, reaching easily the hardness of hard chromium [19,24,29].…”

Corrosion Resistance of Electroless Ni-B-W-Mo Coatings Using Electrochemical Impedance Spectroscopy

“…3(f), respectively. Inflated nodules for Ni-B coatings have been observed by Das and Sahoo [16], in comparison to the as-deposited ones. But, in the present work, such phenomenon was not observed, and only a slight inflation may be seen.…”

“…Ni-B coatings coated at a 60 ºC bath temperature have an excellent corrosion resistance [15]. Das and Sahoo [16] obtained optimal coating bath parameters for achieving enhanced corrosion resistance of Ni-B coatings, using Taguchi's orthogonal array and grey relational analysis. Improvement in the corrosion resistance of Ni-B coatings could be also achieved by thermochemical treatments [6].…”

Corrosion Study of Electroless Ni-P-W Coatings Using Electrochemical Impedance Spectroscopy

“…According to the classic corrosion theory, nanocrystalline materials should have very poor corrosion resistance because their huge quantity of grain boundaries, acting as the preferential corrosion paths, can accelerate corrosion by forming large number of micro electrochemical cells with the matrix. The basic hypophosphite reduced Ni-P and borohydride reduced Ni-B coatings have proved their supremacy in providing improved hardness, corrosion and wear resistance [1][2][3][4][5]. The corrosion resistance of electroless Ni-P coatings is very much dependent on the phosphorous content of the coating.…”