Abstract
Abstract Multilayered Ni coatings were successfully deposited on martensitic stainless-steel substrates by electrodeposition method with intermittent ultrasound. It is a novel kind of multilayered microstructure of stacked-up sandwiches, whose compositions of each monolayer are the same to those of its adjacent layers. The grains of ordinary Ni layers are columnar, vertically to the substrate surface, but the grains of ultrasonic Ni layers grow parallel along the substrate surface. By multilayered structure, the pinholes running through the coating were obviously inhibited, because the multilayered Ni coating can cover the whole surface of the substrate without the direct pinhole passages down to the substrate. Therefore, its corrosion mechanism is the uniform corrosion. For the ordinary Ni coating, the direct corrosion on the substrate can occur through the pinholes, which are the convenient passages for corrosive media to reach the substrate easily. This behavior can lead to the Fe/Ni galvanic corrosion, coating adhesion reduction, and quick formation of coating cracks in the ordinary Ni coating.
Highlights
Electrodeposited nickel coating has wide industrial applications due to its excellent anti-wear and anti-corrosion characteristics
The effect of corrosion protection of the martensite steel substrate by multilayer coatings in contrast to single coatings is ascribed to the selective dissolution of several layers with alternatively varying composition . 23,53,54 A similar preferential dissolution of less noble element from the alloy is a well-known demetallization can occur as confirmed by the literatures . 55,56 in our study, no element difference between the layers can be detected, i.e. no preferential dissolution of element or layers can occur during the corrosion
The results show that did a few pits occur on the sample surface for the ordinary Ni coating, and the representative open corrosion pits (Figure 10b) were generated
Summary
Electrodeposited nickel coating has wide industrial applications due to its excellent anti-wear and anti-corrosion characteristics. The ultrasonic actions bring two important effects: cavitation and acoustic streaming The former phenomena concern the formation, growth, and implosive collapse of bubbles in the solution which were irradiated with high-intensity ultrasound, while the latter ones relate to time-independent and unidirectional flow currents in a fluid due to the presence of ultrasonic waves[30]. An intermittent ultrasonic agitation is used in the Watt Ni electrodeposition course This technique is promising because it is a simple and cost-effective method which is based on the simple combination of a conventional electrodeposition and a high-power ultrasonic irradiation. In this way, a novel kind of multilayered Ni coating, whose composition of each monolayer is the same, was successfully obtained by the ultrasound-assisted electrodeposition process. Its corrosion behavior and the microstructure were investigated systematically, compared with the ordinary Ni coatings
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