In part 1 of this review, emerging practice to realise nanostructured metallic coatings by electrodeposition, anodising and electrophoresis has been considered. Conventional, aqueous electrolytes may be utilised in some cases if workpiece preparation and process conditions are well controlled. Such coatings can provide wear and corrosion resistance or a catalytic or high active area compared to more conventional coatings. An overview of the principles involved in deploying electrochemical techniques to produce nanostructured surfaces and factors influencing developments in this rapidly emerging field were considered. The strategies, which can be adopted to electrodeposit nanostructured metallic coatings, include grain refinement, application of a pulsed current, inclusion of nanoparticles into the coating and the use of nanoporous templates. In part 2, examples of nanostructured coatings and their properties are illustrated with research findings from the authors' laboratory and the literature. Nanostructured metallic coatings include nanocrystalline, functionally graded, nanocomposite and recently introduced hierarchical structures. The potential uses for these coatings in engineering industries (including tribology and energy conversion) are summarised. Finally, future developments necessary to realise and deploy the coatings in increasingly demanding environments are considered.Keywords: Batteries, Electrodes, Electroplating, Electrophoresis, Energy conversion, Fuel cells, Nanoparticle, Nanotube, Tribology
Examples of nanostructured surfacesPart 1 of this review 1 considered the electrochemical processes, i.e. electrodeposition, anodising and electrophoresis, and the principles controlling their deployment, which can be used to create nanostructured surfaces. The first part of the review also lists and defines symbols used in equations and formulae. In Part 2, the authors examine the surfaces themselves, their properties and the applications increasingly opening up for them.
Nanocrystalline coatingsMany design factors must be considered for electroplating good-quality multifunctional nanocrystalline coatings for tribological and other applications. Electroplating process-structure-property relationships are critically important in realising multifunctional coatings, e.g. those which combine controlled electrical conductivity with increased flexibility, such as Ni-graphite 2 or combat wear and corrosion while simultaneously lowering friction, including Ni-SiC 3 The nucleation and growth of nanocrystalline deposits can be tuned by controlling process parameters, such as electrolyte composition, pH, temperature, current density, and current waveform, duration, etc; all these parameters can manipulate the grain size, phase structure and surface roughness, which in turn can design a coating to have multifunctional tribological properties, e.g. wear resistance, corrosion resistance and friction control.For coatings to be effective in tribological applications, stringent criteria can include good adhesion, high mech...