Abstract
The electrodeposition of iron-nickel-chromium coatings is a more environmentally friendly and economical alternative to hard-chrome coatings made from chromium (VI) electrolytes and stainless-steel bulk materials. The aim of the study was to develop a suitable deposition method for thick and low-crack Fe-Cr-Ni coatings. Iron-nickel-chromium coatings were electrodeposited using a more ecological chromium (III) electrolyte with direct current (DC), stepped direct current, and pulse current (PC). The influence of the deposition method on the electrolyte aging, the alloy composition of the coating, and their microstructure was investigated. Corrosion studies of the Fe-Cr-Ni coatings in 3.5% NaCl solution were performed using polarization tests. Furthermore, hardness measurements and scratch tests were carried out to determine the adhesion strength. Phase analyses were performed by X-ray diffraction, and the chemical composition and microstructure were characterized by scanning electron microscopy. Using the stepped DC and PC method, crack-free Fe-Cr-Ni coatings were successfully deposited.
Highlights
Hexavalent chromium has been listed as a substance of very high concern due to its carcinogenic and mutagenic properties and may no longer be used without authorization or exemption under REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) since 21 September 2017 [1]
In order to investigate the influence of current mode and electrolyte aging on Fe-Cr-Ni coatings in terms of their alloy composition, microstructure, corrosion, and wear behavior, the electrolyte listed in Table 1 was used
The element compositions were measured by using energy-dispersive X-ray spectroscopy (EDXS) with area analyses including the metallic species of chromium, iron, and nickel as well as the contamination by carbon and oxygen
Summary
Hexavalent chromium has been listed as a substance of very high concern due to its carcinogenic and mutagenic properties and may no longer be used without authorization or exemption under REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) since 21 September 2017 [1]. Chromium coatings have still been electrochemically deposited from these chromium compounds The advantages of these chromium coatings are their silvery appearance, their high hardness and their very good wear and corrosion resistances [2,3]. This does not even take the decades of experience in industrial electrodeposition into account. While bright-chrome plating is predominantly done from REACH-compliant chromium (III)-containing electrolytes, no comparable properties are currently achievable for hard-chrome coatings. It is, only a matter of time before the chromium-trioxide-based process disappears from the EU’s domestic market. From an economic point of view, it is becoming increasingly attractive to develop and qualify alternative coatings and alloys
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