Influence of the electrolyte composition on the electrochemical dissolution behavior of forged Inconel 718

Abstract

The forged Inconel 718 anodic dissolution at fixed applied current density was investigated in different nitrate sodium based electrolytes, namely in NaNO3 8 wt% and 20 wt%, in NaNO3 15 wt% + NaClO3 20 wt%, and in NaNO3 20 wt% + sulfosalicylic acid 2 wt%. The analysis of the different anodic products on the surface sample, by X-Ray diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray spectroscopy, revealed a presence of oxides mainly constituted of Nb and Ti oxides and a smaller amount of γ″ phase precipitate than in raw material. Inductively coupled plasma (ICP) analysis has shown that the main elements of the matrix (Fe, Cr, Ni) are soluble in all tested electrolytes while Nb content is below the detection threshold in pure NaNO3 electrolyte and in 15 wt% NaNO3 + 20 wt% NaClO3. However, in presence of sulfosalicylic acid, acting as chelating agent, the amount of anodic products on the surface sample has considerably reduced comparatively to other tested electrolytes and Nb was detected by ICP analysis as additional element in the electrolyte. Therefore, this work shows that the Inconel 718 super alloy can be homogenously anodized by the use of an adapted chelating electrolyte, opening up possibilities for efficient electrochemical machining processes.