Electrochemical surface modification of Ti6Al4V: positioning electrochemical machining as a low-valence dissolution pathway for enhanced performance

The automotive, aerospace, biomedical, and other engineering sectors make substantial use of Ti6Al4V titanium alloy, known for its high strength-to-weight ratio, corrosion resistance, and biocompatibility, but it often suffers from poor tribological performance and low surface hardness. To increase durability, a variety of surface modification techniques have been investigated, including chemical etching, shot peening, thermal oxidation, laser surface texturing, and physical vapor deposition. However, these methods frequently entail high thermal input and mechanical stress with limited control over surface chemistry. Electrochemical methods, on the other hand, allow uniform and precise alteration of surface morphology without thermal or mechanical damage. Among these, anodization and plasma electrolytic oxidation (PEO) facilitate hardening and stress-free surfaces but suffer from passive film formation, porosity and micro-cracks, while electrochemical polishing (ECP) yields much better surface finish but at high energy cost and causes passive film formation. In this review, electrochemical machining (ECM), typically viewed as a subtractive method for material removal, is reevaluated as a process for both material removal and functional surface tailoring. Despite its application for removing material, ECM promotes valence-controlled dissolution that favours the formation of lower oxidation states of titanium. It also inhibits the formation of passive films and enables the formation of atomically smooth surfaces. The present study provides a novel theoretical framework for customizing Ti6Al4V surfaces with improved functional and morpho­logical properties by integrating ECM with anodization, PEO and ECP within the broader paradigm of electrochemical surface engineering.