Electrochemical polishing of selective laser melted Inconel 718
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abstract
Additive manufacturing (AM) has gained prominence in the field of manufacturing and is becoming a strong competition to conventional manufacturing technologies such as casting, forming etc. It is used for manufacturing of critical metallic parts for aerospace and automotive industries. Inconel 718, a Ni-Cr-Fe based superalloy, has been extensively used in extreme environments such as nuclear, oil/gas, aircraft applications. Inconel powder can be consolidated by using selective laser melting (SLM) process, which helps in preserving material properties and allows more design freedom. However, one of the drawbacks of additive manufacturing is the rough surface of the produced parts. This study aims to improve the surface finish of Inconel parts manufactured by SLM using electrochemical polishing (ECP) process. This study also compares the SLM parts with the extruded parts of the same metal polished by ECP. The parts are first hand-ground and then polished by ECP process. Inconel 718 is used as workpiece material, titanium rod is used as a tool, and a commercial acid-based electrolyte is used for running experiments. SEM studies are performed on the parts for analysis of results. Pulsed direct currents with varying duty cycles are used to study the effect of off-time during polishing process. Results show that the higher current values are desirable for extruded Inconel parts resulting in shinier surfaces, whereas for SLM manufactured Inconel parts, a very high current can lead to deterioration in surface properties due to presence of non-conductive particles. Successful polishing reduces surface roughness to a sub-micron value (<1 m).
