(Invited) Pulsed Current Deposition: From Nano-Crystalline to Multi-Functional Coatings

The electrochemical deposition of metals and alloys using alternating uni- and bipolar current profiles, in short Pulse Plating technologies, has found the interest of both researchers and companies worldwide in recent years. The use of a modulated current deposition opens a wide field of new possibilities in electrochemical surface finishing as has been discussed at many occasions such as the biannual international conference “European Pulse Plating Seminar” and the Interfinish 2012. While the starting point often has been the aim for nano-crystallinity of deposited coatings, being still one major advantage of pulse plating in the technical awareness of the users, there are nowadays different approaches enabling a combined functionality beyond the nano-crystallinity. Any pulsed electrodeposition process should be based on a fundamental knowledge of the deposition mechanisms and thus requires for the initial set up a profound study of electro kinetics, mass transport limitations and electro-crystallization effects. Electrochemical measurements at laboratory scale and structural analysis of the electrodeposits in dependence on the plating parameters applied will enable the definition of suitable pulse plating sequences. This presentation will discuss the possibilities and applications of generating multi functional layer systems based on the concept of depositing nano-crystalline layers via pulse plating techniques. The electrochemical parameters and concepts for achieving nano-crystalline layers will be explained supported by electrochemical fundamentals. Advantages and limitations of such nano-crystalline coatings will be briefly discussed. Using the results of several (international) fundamental and applied research projects, funded by the European Union strategic research programs, more sophisticated benefits of pulse plated metal alloy coatings will be presented. This will include the incorporation of nano-particles in the metal coating (nano-dispersion coatings), alloy deposition and surface property adjustment. Beside electrochemical experiments for gaining a profound knowledge of the electrolyte properties and the reaction mechanisms, the only way to quantify field line distribution and potential fields, even in a local resolution, are numerical simulation tools. Based on the characteristic electrode kinetics, possible resistive effects at the electrode surface, the general plating conditions (e.g., electrolyte temperature) and the electrolyte properties (e.g., conductivity) a numerical simulation software tool has been used, allowing the exact calculation of current field line distribution and potential fields between two electrodes. Pulse plating with its numerous possibilities to control electrochemical conditions directly at the (substrate) surface, will allow to precisely control the alloy composition of deposited binary and ternary alloys just by adjustment of the pulse parameters. Thermal, electrical properties as well as magnetic properties of the resulting coatings can be adjusted by this method. The underlying nano-crystallinity will additionally increase the resulting layer hardness. The incorporation of particles to form a (nano) dispersion coating will provide hardness and wear resistance better and more stable than pure nano-crystalline coatings. This presentation will be complemented by several examples of the industrial use of pulse plating for high-tech components and mass production parts.