Multiscale Roughness Characterization of Electropolished 316L ALM Steel By Power Spectral Density Post-Treatment

Abstract

Electrolytic polishing (EP) is a well-known technology which may replace mechanical polishing in finishing treatment of complex geometry substrates produced by additive manufacturing (AM). This consists in an anodic dissolution process, allowing a mirror finish to be obtained by uniform roughness reduction on metallic parts immediately after the machining step. This is achieved by controlling electrolyte nature and operating parameters such as dissolution potentials, process duration and temperature [1]. Nevertheless, in the specific case of additive manufacturing, where high level of roughness can be observed, it is important to discriminate the microscopic and macroscopic scales of etching. The roughness value can be measured at different scales by several technics (mechanical sensor, optical profiler, AFM…), but the results (Ra, Sa…) are dependent on the spatial resolution of the device and on the measurement procedure like cut-off application. A way to overcome this problem consists in making these parameters independent of the roughness scale by integrating the fractal dimension of topographic records [2]. In this study, 316L stainless steel samples obtained by additive manufacturing were electropolished and compared to raw and mechanically polished samples. The characterization of the surface roughness was carried out by optical profilometry, and the 2-D data were analyzed to plot Power Spectral Density as a function of spatial frequency (PSD) [3]. Then, the curves obtained are fitted by the Weierstrass-Mandelbrot function to determinate the fractal dimension, which allows quantification of the surface irregularity level [4]. Acknowledgments : the authors would like to thank the IRT-M2P program AFTER ALM for its financial support. [1] C. Rotty, A. Mandroyan, M.-L. Doche, and J. Y. Hihn, Surf. Coat. Technol., 307 Part A, 125–135 (2016) [2] Majumdar, A., Tien, C.L.: Fractal characterization and simulation of rough surfaces. Wear 136(2), 313–327 (1990) [3] Prashant Pendyala, M. S. Bobji, Giridhar Madras. Evolution of Surface Roughness During Electropolishing, (2014). Springer Science Editions [4] S. Panda, A. Panzade, M. Sarangi, S.K.R. Chowdhury, Journal of Tribology, 139 031402-1/9 (2017) Figure 1