A Comparative Study on Micro-electro-discharge-machined Surface Characteristics of Ni-Ti and Ti-6Al-4V with Respect to Biocompatibility

Ti-6Al-4 V (grade 5 titanium alloy) and NiTi (shape memory alloy) are two commonly used materials for biomedical orthopedic and orthodontic applications. The surface characteristics of the biomedical implants play a significant role on the biocompatibility and mechanical strength of the implants. The objective of this study is to investigate and compare the surface characteristics of NiTi shape memory alloy (SMA) and Ti-6Al-4 V alloy after machined using micro-electro-discharge machining (micro-EDM). The machined surfaces were analyzed for topography, composition, migration of materials and microhardness. The results showed that NiTi SMA produced comparatively smoother surface finish. The analysis of elemental composition indicated migration of materials to the workpiece from the dielectric and the tool electrode. There is formation of TiO2 and NiTiO3 layers on the machined surfaces of Ti-6Al-4 V and NiTi respectively. The surface microhardness increased in both NiTi and Ti-6Al-4 V workpieces after micro-EDM due to the formation of the oxide layers. The formation of oxide layers can be beneficial for both materials when used as biomedical implants, as commercial implants contain protective oxide coatings to minimize the corrosion inside human body.