Abstract
Additive manufacturing (AM), or 3D printing, has revolutionized the manufacturing world through its rapid and geometrically intricate capabilities as well as economic benefits. Additive manufacturing techniques have manufactured numerous alloys and metals up to the recent date. Selective laser melting, among others, has gained huge interest from the manufacturers towards the technology adoption in the manufacturing sector. Much research has been conducted to improve manufacturing consistency within additive manufacturing techniques. Despite all the efforts to improve the technology, surface roughness is still a paradox in the additively manufactured parts. The surface roughness paradox raises the question, are there post-processing techniques that can reduce the surface roughness of the built specimen without affecting the geometry? Therefore, the hypothesis of this research question was that novel electropolishing without using mineral acids can improve the surface roughness of the built specimens. Due to the application of built alloys in harsh environments, the other question was, can electropolishing improve the corrosion resistance behavior of the electropolished alloys? In this regard, electropolishing was expected to improve the corrosion resistivity behavior of the built alloys because electropolishing was designed to remove material from the surface equivalent to the growth of oxide layers would protect the alloy against corrosion in harsh environments. Therefore, this work presents electropolishing selective laser-built Ti-6Al-4V with mixed metal salts as electrolytes. The corrosion behavior of the electropolished specimen was also studied to improve the structural integrity of the parts by electropolishing. Electropolishing media was formulated with mixed metal salts, with ethanol and triethanolamine as solvents instead of water. The SLM-built Ti-6Al-4V samples were electropolished with 0.2 Acm-2 and an immersion time of 30 minutes at 30 oC. The surface roughness of the built specimen was reduced from 45 m to 9 m. The x-ray photoelectron spectroscopy revealed that electropolishing had enabled the growth of the titanium oxide, TiO2, layer. The x-ray diffraction further revealed that the oxide layer on the surface was dominated by rutile. Concerning structural integrity, corrosion studies revealed that electropolishing of the alloys improves the resistivity behavior towards degradation. The electropolishing specimen had a lower corrosion rate than the mechanically polished specimen. The electrochemical impedance data revealed the electrode surface of electropolished species as
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non or less conductive, reducing the charge transfer between electrode and solution interface. The wear properties of an electropolished and mechanically polished specimen did not have significant differences. This means that the oxides formed on the surface of electropolished specimens do not offer improvement towards tribo properties.