Effect of current density on electrochemical machining process of laser powder bed fusion manufactured Inconel 718

Abstract

Electrolytic jet machining (EJM) has been widely recognized as one of the effective methods for the surface post-processing of the laser powder bed fusion (LPBF)-components. However, this concept remains challenging due to the limited machining allowance of the LPBF-components and the complexed anodic dissolution behavior, which determine the dimensional accuracy and surface quality of the machined workpiece, respectively. In this work, high current densities ( ≥ 100 A/cm²) are novelly employed to investigate the leveling ratio and transpassive dissolution behavior of LPBF-Inconel 718 for the first time. Compared to 100 A/cm², 200 A/cm² improves the leveling ratio to 58.9 % from 57.1 % when the surface roughness is less than 1 µm. However, the high current density up to 200 A/cm² still cannot inhibit the selective dissolution of the inhomogeneous microstructure, which limits further reduction of the surface roughness. A high current density leads to a rougher micro-surface on horizontal section than low current density, caused by more Nb oxides attached on the horizontal section at high current density generate from continuously distributed Nb-segregation γ phase along the machining depth direction. In addition, the local fine dendrites on vertical section result in a smooth EJM-surface, owing to the relatively uniform dissolution. This investigation provides systematic understanding of leveling process and transpassive dissolution behavior under high current density with complex surface and microstructure, which can further promote synergetic improvements of the surface integrity and dimensional tolerance through controlling the EJM parameters.