Anodic Dissolution Behavior of Passive Layer During Hybrid Electrochemical Micromachining of Ti6Al4V in NaNO3 Solution

Abstract

Titanium and its alloys are considered as difficult to cut material classes, and their processing through the traditional machining methods is a painful task. These materials have an outstanding combination of properties like high specific strength, excellent corrosive resistance, and exceptional bio-compatibility; therefore, they have broad fields of application like aerospace, MEMS, bio-medical, etc. Electrochemical micromachining (ECMM) is a very vital process for the production of micro-domain features in difficult-to-machine materials. The machining issue with ECMM for titanium and their alloys is the passive layer formation, which hinders the dissolution and causes stray removal. To overcome these issues, a hybrid ECMM approach has been proposed by using a diamond abrasive tool combined with ECMM. The present study focuses on the detailed characterization of the passive layer formed using the hybrid approach. Through the use abrasive tool, the abrasive grits scoop the passive layer by the mechanical grinding action, formed in micro-drilling on the Ti6Al4V alloy to expose a new surface for further dissolution. The micro-holes were produced incorporating the abrasive tool and then compared by the holes created using a cylindrical tool (tool without abrasive). The taper and the stray dissolution of the micro-holes were also compared, produced at different applied potentials. The minimum average entry overcut and exit overcut of the hole were obtained as 29 µm and 3 µm, respectively, also a micro-hole with the lowest taper of 2.7°, achieved by the use of the abrasive micro tool.