Abstract
Currently, Ni-Cr coatings are widely used in a number of important applications due to their excellent properties. In this study, Ni-Cr alloys were electrodeposited from citrate bath onto Cu substrates by using different values of applied current densities. The effects of plating deposition current density on morphological and structural characterization of Ni-Cr electrodeposited coatings were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Microhardness of the coatings is also evaluated using Vickers’s microhardness. Potentio-dynamic polarization and electrochemical impedance spectroscopy (EIS) tests in 3.5 wt % NaCl solution were used to evaluate corrosion résistance of Ni-Cr coatings. The results showed that the surface morphology of the all coatings contained micro cracks and pores. XRD patterns indicate the formation of Ni-Cr and Cr3Ni2 phases. Microhardness measurements show that all Ni-Cr samples are harder than copper substrate. Electrochemical tests show that 3 A.dm-² is an optimal value of applied current density in the sense of the least value of Ecorr = -12.3 mV and the best charge transfer resistance Rp = 303.03 Ω.cm².
Highlights
Surface failures, one of the more important problems encountered in the industry, are due to wear, corrosion, fatigue, etc. [1]
Before scanning electron microscopy (SEM) characterization, it was remarkable that the electroplating alloys become darker with increase of current density, which can be caused by the formation of hydroxide compounds and changes within the morphology
All the deposits show nodular surface morphology with microcracks, which increase by increasing the current density
Summary
One of the more important problems encountered in the industry, are due to wear, corrosion, fatigue, etc. [1]. In order to improve the properties of the surface against corrosion and increase the service life of metallic components, various modifications could be applied such as alloying a nickel based layer with other element like Mo, W, Al, SiC, Co [2,3,4,5,6,7]. Despite these coatings, Ni-Cr alloys exhibit better corrosion resistance and superior hot corrosion resistance due to the formation of a continuous chromia scale [8, 9] which permits the use of these alloys in many industrial applications.
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