Electroplated alloys

The electrochemical preparation of alloys is almost as old as the electroplating of pure metals: brass deposits were developed as early as 1840. Over the last ten years or so, the electroplating of alloys has been the subject of a very high number of publications, close to a hundred each year. This is due to the large number of possible alloy combinations and the wide range of potential practical applications.

This technique not only modifies the surface properties of materials, but also creates structures, or even nanostructures, with specific properties. Both functional and decorative coatings can be produced, with thicknesses ranging from fractions of a micrometer to tens of micrometers. Compared with competing technologies such as physical vapour deposition, electroplating is relatively simple to implement, well suited to mass production such as high-speed deposition for automotive sheet metal, or barrel deposition for small parts. It can also be used to coat complex substrates.

Electroplated alloys often have different or even superior properties to those of the metals from which they are derived: superior hardness, corrosion or wear resistance, interesting magnetic properties, etc. Both composition and morphology are highly dependent on hydrodynamic conditions, and can be modified by the use of potentials or pulsed currents.

The crystalline structure and phases present may be identical or different to those of metallurgically prepared alloys. In some cases, supersaturated solid solutions can be obtained, the precipitation of granules of a second phase can modify certain properties, and structural hardening can be achieved by heat treatment. Depending on electrolysis conditions and alloying elements, grain size can be controlled, and nanocrystalline alloys can be produced. A great deal of work is focusing on the deposition of nanocrystalline structures, such as nanowires in "template" structures like nanoporous membranes or anodized aluminum.

However, these electrochemical processing techniques are still largely based on empirical methods, and there is a gap between fundamental research into the kinetics of electrocrystallization processes and industrial practice. A study of elemental codecharge mechanisms is essential to control, or even model, the composition of alloys and the possible distribution of elements on the surface, and to enable electrolytes to be formulated on a more rational basis.