Modelling Investigation of the Impact of Several Process Parameters on the Growth of the Viscous Layer during the Electropolishing

Abstract

Electrochemical polishing (EP) is of great interest because it is able to deal with small parts exhibiting high complex shapes and/or material hard to be polished. Electropolishing is an electrolytic process based on the anodic dissolution of the workpiece under constant current or potential. Previous work done on stainless steel 316L shows the ability of the process to obtain smooth and bright surfaces [1]. The mechanisms describing EP are not yet fully understood, but several mechanisms can be taken into account for its description and prediction. Jacquet’s theory is based on the influence of an electric resistance gradient [2]. Elmore will then complete it with the gradient of concentration in metal cation [3,4]. Diard and al proposed the role of so called “acceptor” species [5]. While Hoar and Mowat’s work are based on the formation of an oxide layer on the surface [6]. All theories have in common the establishment of a viscous layer (solid or liquid) that governs the process. On this basis, it is possible to propose a numerical approach for the simulation of the viscous layer formation during electropolishing of stainless steel 316L and Inconel parts. The objective is to demonstrate the impact of various process parameters (electrochemical parameters, electrolyte nature and concentration as well as hydrodynamic conditions) on the growth and the stability of this layer. The figure illustrate the simulation of the viscous layer growth during the electropolishing of a plate at the bottom taking into account the circulation of the electrolyte from the left to the right. [1] C. Rotty, A. Mandroyan, M-L Doche, J-Y Hihn, Surface & Coatings Technology vol.307 p125–135 (2016). [2] JACQUET, P.A., Electrolytic method for obtaining bright copper surfaces, Nature 135 (1935) 1076. [3] ELMORE, W.C., Electrolytic Polishing, J. Appl. Phys. 10 (1939) 724–727, http://dx.doi.org/10.1063/1.1707257. [4] ELMORE, W.C., Electrolytic Polishing II, J. Appl. Phys. 11 (1940) 797–799, http://dx.doi.org/10.1063/1.1712738. [5] DIARD, J.P., LANDAUD, P., LE CANUT, J.-M., LE GORREC, B., Interprétation cinétique du palier de polissage électrochimique des métaux, 6ème forum sur les impédances électrochimiques, Montrouge, 1992. [6] HOAR, T.P., MOWAT, J.A.S., Mechanism of electropolishing, Nature 165 (1950) 64–65. Figure 1

Fabrication of microneedles using wire electric discharge machining and improving surface quality by electrochemical polishing

“…The blunt MN tip gets sharpened because of the elevated etch rate due to the high diffusion coefficient and localized current density at the protruding portions, edges between the top surface and the side faces from both the vertical and lateral directions. The low reduction in geometry near the base of the MNs (figure 26) can be attributed to the reduced etching rate near the base, which could be explained by the reduced diffusion coefficient based on the concentration gradient of the Nernst diffusion layer [66][67][68].…”