A Study on the Surface Composition and Migration of Materials and Their Effect on Surface Microhardness during Micro-EDM of Ti-6Al-4V

This study aims to investigate the effect of machining parameters on the surface topography and composition of Ti-6Al-4V after micro-EDM as well as the effect of elemental composition on the surface microhardness. The surface topography has been studied in terms of quality of machined surface, crater sizes, and the presence of surface defects. Statistical analysis was carried out to study the influence of micro-EDM process parameters, i.e., voltage, capacitance, discharge energy, electrode rotational speed, and the electrode coating, on the elemental composition of the machined surface. It was found that the crater size, and hence the surface finish, was dependent on the electrical parameters only, with more pronounced effect of capacitance over voltage. The 60 V and 30 pF combination resulted in crater size as small as 1 µm, whereas crater size of 12 µm was obtained using a combination of 4700 pF and 112 V. Although smaller capacitance resulted in smaller crater sizes, it also increased the chances of defects or deposition of debris on the machined surface. There was migration of material from the tool electrode, dielectric oil, and atmosphere to the workpiece surface, which influenced the surface topography, crater sizes, and surface microhardness. The effects of non-electrical parameters on the relative percentage of various elements were found to be statistically insignificant. The surface microhardness was found to increase slightly due to the surface modification after EDM. The reason for increase in surface microhardness was identified as the migration of tungsten from the tool electrode and carbon from the dielectric. The maximum surface microhardness of 455 HV was obtained at a surface composition after micro-EDM containing 7.96% C and 9.69% W, where non-machined Ti-6Al-4V surface does not have any carbon or tungsten on the surface.