Electropolishing of Re-melted SLM Stainless Steel 316L Parts Using Deep Eutectic Solvents: 3 × 3 Full Factorial Design

Abstract

SummaryThis three levels three factors full factorial study describes the effects of electropolishing using deep eutectic solvents on the surface roughness of re-melted 316L stainless steel samples produced by the Selective Laser Melting (SLM) powder bed fusion additive manufacturing method. An improvement in the surface finish of re-melted stainless steel 316L parts was achieved by optimizing the processing parameters for a relatively environmentally friendly ('green') electropolishing process using a Choline Chloride ionic electrolyte. The results show that further improvement of the response valueaverage surface roughness (Ra) can be obtained by electropolishing after re-melting to yield a 75% improvement compared to the as-built Ra. The best Ra value was less than 0.5μm, obtained with a potential of 4 volts, maintained for 30mins at 40C°.Electropolishing has been shown to be effective at removing the residual oxide film formed during the re-melting process. The material dissolution during the process is not homogenous and is directed preferentially towards the iron and nickel, leaving the surface rich in chromium with potentially enhanced properties. The re-melted and polished surface of the samples gave an approximately 20% improvement in fatigue life at low stresses (approximately 570MPa). The results of the study demonstrate that a combination of re-melting and electropolishing provides a flexible method for surface texture improvement which is capable of delivering a significant improvement in surface finish whilst holding the dimensional accuracy of parts within an acceptable range.2

Corrosion of Additively Manufactured Stainless Steels—Process, Structure, Performance: A Review

“…), [163][164][165][166][167][168][169][170][171][172][173][174] and chemical and electrochemical polishing. [175][176][177] Schaller, et al, showed that industrial silica grit blasting used to knock off partially fused powder caused active corrosion of SLM 304L at open circuit in quiescent 0.6 M NaCl. 101 They attributed this to incomplete removal of surface voids, high imparted strain, and embedded silica particles in the matrix.…”

Comparison of Different Heat Treatment Processes of Selective Laser Melted 316L Steel Based on Analysis of Mechanical Properties

“…Trelewicz et al indicated that the corrosion resistance of SLM-processed 316L steel was reduced because of the inhomogeneous solute distribution [ 17 ]. Due to the worse mechanical properties of SLM-produced elements, numerous studies are being conducted related to process parameter modification [ 18 , 19 , 20 ], in-process material annealing using laser re-melting [ 21 , 22 ], or post-process heat treatment [ 23 , 24 ]. All mentioned sources indicate the possibility of improvement of the mechanical properties.…”

Electropolishing of Laser Powder Bed-Fused IN625 Components in an Ionic Electrolyte

“…The temperature increase results in an exponential increase of current density and affects the electrochemical reactions [19]. A study on EP of re-melted LPBF 316L stainless-steel using ILs [23] showed that at very high electrolyte temperatures, the material dissolution and surface roughness increase due to an increased current density, which may result in a non-homogeneous material dissolution. As shown in Figure 3, the current density plateau increases as the temperature increases from 25 to 50 °C.…”

“…The passivation mechanism is limited by the diffusion of acceptor anions to the dissolving metal The temperature increase results in an exponential increase of current density and affects the electrochemical reactions [19]. A study on EP of re-melted LPBF 316L stainless-steel using ILs [23] showed that at very high electrolyte temperatures, the material dissolution and surface roughness increase due to an increased current density, which may result in a non-homogeneous material dissolution. As shown in Figure 3, the current density plateau increases as the temperature increases from 25 to 50 • C. In addition, the temperature increase also intensifies the chemical reactions related to the super-saturation of the salt film in the i-peak region by increasing the value of the current density peak.…”