Highly Efficient Inner Surface Polishing of Fe-Cr-Ni Alloy Cylinder via Isotropically Tuned Electrochemical Etching

Abstract

The inner surface of a Fe-Cr-Ni alloy cylinder produced through extrusion is processed by electrochemical isotropic etching polishing (IEP). The electric field simulation predicted a high current density at protrusions, pertinent for passivation layer breakdown and proficient dissolution. Initially, the effect of cathode diameter and current density was investigated on planarization and current efficiencies, material removal rate, and etching behavior of IEP of ground Fe-Cr-Ni alloy. IEP of the as-extruded inner surface realized a 94% improvement in the Sa roughness (from 5.33 to 0.34 µm), while the initial surface morphology and instantaneously breaking metal lumps seriously influenced the final Sa roughness and polishing duration. Furthermore, the as-extruded and ground Fe-Cr-Ni alloy substrates were polished simultaneously, whereupon the IEP of the latter produced a mirror-like, highly uniform, and mechanically superior surface with 37% higher planarization efficiency and 19% greater wall thickness. However, due to falling off metal lumps, the IEP of the as-extruded substrate registered higher current efficiency (⁓38%) than the ground substrate (⁓30%). IEP realizing a rapid improvement in the line profile and Ra roughness of the ground Fe-Cr-Ni alloy shows that IEP can efficiently improve the performance of functional inner surfaces to application grade.