Viscous layer formation during electropolishing and nano-texturing of 316L stainless steel in ethylene glycol-perchloric acid using current controlled anodizing

Tools

Regent, Christine and Doche, Marie-Laure and Hallez, Loïc and Vuillemin, Bruno and Vignal, Vincent and Boucher, Aurélien and Roy, Sudipta (2026) Viscous layer formation during electropolishing and nano-texturing of 316L stainless steel in ethylene glycol-perchloric acid using current controlled anodizing. Surface and Coatings Technology, 522. 133129. ISSN 0257-8972 (https://doi.org/10.1016/j.surfcoat.2025.133129)

[thumbnail of Regent-etal-SCT-2025-Viscous-layer-formation-during-electropolishing-and-nano-texturing]
Preview
 Text. Filename: Regent-etal-SCT-2025-Viscous-layer-formation-during-electropolishing-and-nano-texturing.pdf
Final Published Version
License: Creative Commons Attribution 4.0 logo
Download (16MB)| Preview

Abstract

Although there has been a growing interest in nanoscale texturing of steel, there have been few papers focused on the processes accompanying the phenomenon. The current work examines if the formation of a viscous layer is a necessary condition for surface texturing of steel, and probes the underlying processes leading to pattern formation formation in an electrolyte originally developed for electropolishing. The investigation involved nanotexturing SS grade 316L anodization using an ethylene glycol-perchloric acid electrolyte and constant current between 1 – 10 A·dm-2. During the experiment, the viscous layer formation or surface modification as well as the potential response were simultaneously monitored. Two different electrode orientations, horizontal and vertical, are examined. The horizontal orientation stops convection at the vicinity of the electrode whereas the vertically oriented electrode would have convective flows at the electrode vicinity. The effect of surface preparation, through different mechanical polishing conditions, on the pore formation has also been examined. The results clearly showed the formation of viscous layer at the surface preceding surface texturing. The pore size was controlled by the applied current and reached 370 nm, with optimal current density being 5 A·dm-2. Visualization of the electrode surface showed that one achieved a stable viscous film at a horizontal electrode. For the vertically oriented electrodes gravitational flows of the viscous layer were observed. The resistive contribution of the viscous layer was assessed around 0.50 – 0.70 Ω·dm². Analysis of potential changes also showed a voltage surge occurred during the formation of a compact layer. It was found that just at the point of completion of viscous layer, texturing commences, indicating that formation of a viscous layer or salt film is essential to the texturing process. Further analysis using the Sand equation showed electropolishing occurred due diffusion-controlled transport through the viscous film.

ORCID iDs

Regent, Christine, Doche, Marie-Laure, Hallez, Loïc, Vuillemin, Bruno, Vignal, Vincent, Boucher, Aurélien and Roy, Sudipta ORCID logoORCID: https://orcid.org/0000-0002-3399-035X;
CORE (COnnecting REpositories)