Investigations of surface integrity, bio-activity and performance characteristics during wire-electrical discharge machining of Ti-6Al-7Nb biomedical alloy

Abstract

In present research, Ti-6Al-7Nb was machined using wire-electrical discharge machining (WEDM). This material has high strength and the characteristics are similar to Ti-6Al-4V; but in the cytotoxic vanadium was replaced by niobium. As an application in biomedical, the bioactivity and surface characteristics of material should be high. Therefore, in present work the bioactivity and surface integrity of machined surface was investigated. The WEDM responses were optimized using a hybrid approach of Taguchi-Regression analysis and Modified Genetic Programming (TRMGP). Response characteristics were predicted at 95% of confidence interval for both the population and confirmation experiments. The empirical models for surface roughness (SR) and material removal rate (MRR) have been generated using regression analysis (RA) and solved by modified genetic programming. The input machining variables were servo voltage (SV), pulse off-time (Toff) and pulse on-time (Ton) for the machinability of Ti-6Al-7Nb. The experimental layout was designed as per the Taguchi based orthogonal array (OA). The predicted and experimental values for MRR are 7.3996 mm3 min−1 and 7.13 mm3 min−1, while that of SR are 13.32 μm and 13.21 μm respectively. The machined surface was checked for bioactivity in the presence of simulated body fluid (SBF). It was found that the surface machined by wire electric discharge machining enhances the bioactivity sites for the development of hydroxyapatite. The results of the present work confirm the suitability of hybrid approach of TRMGP to optimize WEDM response characteristics for enhancing machinability of Ti-6Al-7Nb for bio-medical applications.