The Electropolishing of Additively Manufactured Parts in Titanium: State of the Art

Abstract

Recently, additive manufacturing technologies have begun to play a significant role in the industrial field due to the possibility to build complex, near‐net‐shape, and porous parts, optimizing costs, and time processing. Simultaneously, the high roughness of additively manufactured parts remains a critical drawback, limiting their use like an as‐built component. Therefore, postprocessing treatments are needed. The electropolishing (EP) treatment could be ideal for simple, complex, or porous parts characterized by low surface quality. Herein, it is aimed to provide the state of the EP treatment's art carried out, to date, on additively manufactured parts made of titanium and Ti6Al4V alloy. A scientific literature research on EP of additively manufactured titanium and Ti6Al4V alloy is conducted using the Scopus database. The evaluation of recent research, still very few to date, reveals that a significant reduction of the roughness can also be achieved in complex shape additively manufactured parts. Although the EP is a versatile technique to reduce the roughness of additively manufactured parts, further studies are needed to improve its effectiveness, especially for complex and porous structures, to reduce the environmental impact of the materials used.

Electropolishing with Low Mass Loss for Additive Manufacturing of Ti6Al4V in Zinc Chloride-Urea Deep-Eutectic Solvent

“…In this regard, electropolishing of Ti6Al4V alloys in this DES system improved surface hydrophobicity and stability, thereby also improving electrochemical corrosion resistance. 35 In order to investigate the effect of electropolishing treatment on the electrochemical corrosion behaviour of Ti6Al4V alloy in a 3.5% NaCl aqueous solution, the vertical side surface of AMed specimens was chosen to assess dynamic-potential steady-state polarisation curves and perform EIS testing. The corresponding comparison was also made with melt-cast fabricated Ti6Al4V sheet specimens (Fig.…”

“…Therefore, not only did polishing reduce the dissolution of titanium ions, but also the high viscosity of the solvent made it difficult for titanium ions to diffuse, hindering the formation of TiCl 4 yellow mucosa, and the combined effects resulted in relatively low surface mass loss during high temperature polishing. Additionally, to compare traditional acidic polishing solutions with this DES composed of salt and alcohol, according to a previous report on polishing in perchloric acid glacial acetic acid for titanium alloys in only 20 min, 35 the mass loss of titanium alloys reached 16.29%, much higher than for the glycol-MgCl 2 system and the ZnCl 2 -urea system. Therefore, it was concluded that the extent of mass loss of titanium alloys during electropolishing in green non-aqueous solvents was significantly reduced.…”

Green Approach for Electropolishing Surface Treatments of Additive Manufactured Parts: A Comprehensive Review

“…The additively built-up pieces, very often, present superior mechanical and electrochemical properties compared to the casting counterparts [5], but one of their drawbacks is represented by their poor surface finish, affected by high roughness (in some cases around 50 µm [6]), together with edges, corners, and discolouration [7]. The roughness defects arise from balling and rippling effects, the presence of stocked un-melted or partially melted particles (see Figure 1), the stair-step effect, when angled or curved parts are built, the presence of oxide particles [8], micro-crack, microporosity [9], and droplet columns [10]. Adapted from [6], with permission from Elsevier, 2020.…”

Electropolishing and Shaping of Micro-Scale Metallic Features

“…The amount of metal dissolution is governed by Faraday’s law, which is related to the amount of metal removed for a given current and time. This can be expressed in mass “ m ”, volume “ V ”, and height “ h ”, as per Equations (1)–(3), respectively [ 45 ]. where “ A ” is the surface area of a workpiece, “ Q ” the electric charge, “ a ” the atomic molecular weight, “ ρ ” the density, “ Z ” the valence of ions, and “ F ” the Faraday constant, “ I ” the current, and “ t ” the time.…”