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Microstructural and elecrochemical characterization of Ti-6A1-4V ELI alloy

Topçuoğlu, Melih
In this study, the evolution of structure and the relationship between microstructure and corrosion behavior of the Ti-6Al-4V ELI (Extra Low Interstitial) alloy was investigated in Ringer’s solution at 37 ± 0.1 oC. Initially, different heat treatments were performed in order to obtain several microstructures which were; Widmanstätten α for furnace cooling (FC), basket-weave α for air cooling (AC), martensite (α') for water quenching (WQ) from 1060 oC, and aged martensite for ten hours at 500, 600, 700, 800, 900 oC. The microstructural characterizations were done by using SEM and X-ray Diffraction technique. Finally, the corrosion tests were accomplished in Ringer’s solution and NaF added Ringer’s solution by using open circuit potential and anodic polarization techniques, respectively. The results showed that vanadium element removal from martensite phase and unit cell volume increase were detected during aging due to the replacement of vanadium with titanium atoms. According to the alloying element distribution throughout the microstructure, the passive film formation due to equilibrium corrosion conditions was better in FC specimen than AC and WQ specimens. But during anodic polarization, the stability of the film in high Cl- ion concentration medium was more resistant to dissolution for WQ and aged specimens. As a result, the alloying element distribution underneath the passive film seemed to have an important role on the film formation and its stability. However, in non-equilibrium conditions, the passive film formation tendency due to the addition of NaF at 0.2M decreased because of the detrimental effects of F- ions.