TOPOCROM – Rethinking the fundamentals of electrocrystallisation

Abstract

This article describes the scientific electrochemical and material-technical background of a technology with which hard chrome layers can be specifically provided with a topography, i.e. with a microstructure. The structure is characterised by the formation of spherical cap-shaped structural elements. This process, called TOPOCROM®, has been successfully available on the market for some time and is applied exclusively by a German job plater. As is often the case in the electroplating industry, which is characterised by medium-sized companies, the original development was based on the trial and error principle. With increasing industrial success, the need to better understand the basic mechanisms grew, which led to the investigations presented in this paper. First, theoretical considerations are made based on the fundamentals of electrocrystallisation. These lead to the assumption that a change in the crystallisation form occurs when the structures are generated by the so-called current ramp. This assumption was verified by experiments in which flat discs were plated and then measured using EBSD. This proved that the suspected change in electrocrystallisation actually takes place, more precisely from a strongly field-oriented {111} texturing to an unoriented crystal form. On this basis, a growth model for the special layers was then developed.