Crystallinity, surface morphology, and chemical composition of the recast layer and rutile-TiO2 formation on Ti-6Al-4V ELI by wire-EDM to enhance biocompatibility

Abstract

In this study, the surface morphology, chemical composition, and crystallography of the recast layer on wire electrical discharge machining (wire-EDM) modified Ti-6Al-4V ELI were investigated through scanning electron microscopy, backscattered electron imaging, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The characteristics of the two tailored cutting strategies, namely, main cut and finish trim cut, were evaluated in terms of micro-cracks, micro-pores, recast layer thickness (RLT), surface roughness (SR), phase transition, and micro-hardness. In addition, the relative changes of the SR, RLT, and kerf width were demonstrated with regard to peak current and pulse spacing. Noticeably fewer amounts of micro-cracks, micro-voids, remarkable truncation of RLT and SR, and nanoporous structure were attained at finish trim cut mode. It was also found out that an α → α′ + rutile-TiO2 phase transition occurred on the recast layer of wire-EDM modified sample at finish trim cut. Furthermore, recast layer showed higher micro-hardness compared to that of the heat-affected zone and bulk material. In essence, the wire-EDM finish trim cut treatment is a potential technology to feasibly enhance the biocompatibility for Ti-6Al-4V ELI alloy through the formation of rutile-TiO2 and amelioration of the surface morphology.