Study of anodic dissolution of 100Cr6 Steel during electrochemical machining in oxidizing and reducing electrolytic environments.

Abstract

Electrochemical machining (ECM) has been widely recognized as a promising technique that plays an important role in the fabrication of micro textured surfaces of engineering materials. The advantageous features of ECM, like high material removal rate (MRR) and surface finish, have been found effective to improve the efficiency of machining components compared to the other processes. However, the machining precision of ECM has still limited due to the formation of a passive adherent oxide layer over the specimen surface. These factors adversely affect the MRR and surface roughness (Ra). The high current density (20-150 A/cm2) can be used to enhance the MRR, but the process becomes vulnerable to energy consumption, resulting in poor surface finish. These limitations of ECM can be minimized by employing a suitable electrolytic environment. This paper shows the anodic dissolution characteristics of 100Cr6 Steel in oxidizing and reducing electrolytic solutions. The reducing electrolyte containing CuSO4 mixed NaCl that maintains the low valence state of substrate metal ion which, in turn, facilitates higher MRR and improves the surface finish quality. Similarly, the oxidizing electrolytic solution composed of K2Cr2O7 mixed with NaCl allows higher anodic dissolution but ensuing Cr2O7—ion form a passive layer on the metal surfaces. In two different electrolytic environments, transpassive anodic dissolution was found to occur. Comparable dissolution mechanisms have been studied using cyclic voltammetry (CV) technique and UV-visible spectrophotometry. Micro-images of scanning electron microscopy (SEM) emphasize that metal surfaces are exposed more in existing oxidizing environments and less in reducing environments.