Effect of electrical discharge machining (EDM) bath composition on long-term corrosion of Ti-6Al-4V in simulated body fluid

Ti-6Al-4V (Ti64) alloy is a widely used bioimplant material due to its excellent properties. However, long-term exposure to body fluids can lead to corrosion, a concern given increasing lifespans. Electrical discharge machining (EDM) can improve Ti64 corrosion resistance at long term. This study investigates the long-term corrosion behaviour of Ti64 in simulated body fluid (SBF) after EDM treatment using different bath compositions (oil, water, and hydroxyapatite dissolution (HA)). Electrochemical and microscopy techniques were used to analyse corrosion mechanisms over immersion periods ranging from 2 h to 3 months. Results show that EDMtreated samples in water exhibited the highest corrosion resistance, while those processed in oil possessed the lowest. Especially, the corrosion resistance of samples treated in water and HA remained constant over time, unlike the non-EDMed and oil-treated samples. Furthermore, all samples exhibited evolving corrosion mechanisms over time, with faster deposition of SBF elements observed on oil and HA-treated samples, suggesting enhanced biointegration potential. The thicker deposited SBF layer on these samples further supports the potential of these EDM treatments to improve the biointegration of Ti64 implants.