UBC Theses and Dissertations
A study on the corrosion and electrochemical properties of Electron Beam Melted Ti-6Al-4V for biomedical applications Mohammadali, Shahsavari
The corrosion properties and passive film behaviour of wrought (WR) and electron beam melted (EBM) Ti-6Al-4V (Titanium Grade 5 or TG5) were compared in simulated physiological solution. Microstructural characterization was performed using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) to correlate the microstructural characteristics to corrosion resistance. The "bimodal" and "basket-weave" morphologies were observed for WR and EBM samples, respectively. Electrochemical measurements were also carried out for the evaluation of corrosion and passive film properties. Open circuit potential (OCP) and potentiodynamic polarization (PDP) measurements showed that the EBM sample has lower corrosion current densities. After choosing three potentials in the passive region from the PDP curves (300, 500, and 700 mVAg/AgCl), a passive film was formed on the EBM and WR TG5 samples using potentiostatic polarization (PS). Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis were used to assess the passive film properties in Ringer’s physiological solution at 310.15 K (37±1 °C). A more compact and protective passive film developed on the EBM sample at each film formation potential. M-S measurements revealed that the passive film on both WR and EBM samples were n-type semiconductors with fewer donor densities (ND) for the EBM sample. Furthermore, the spontaneously formed passive layers on the surface after immersion for 1 hour (at OCP) were compared. EIS results showed that the passive layers have duplex characteristics with higher corrosion resistance for the EBM sample. Moreover, the naturally formed passive films on the WR and EBM samples showed n-type characteristics, and the donor density was lower for the EBM sample. Immersion tests (IT) were also carried out at a controlled temperature and time to measure the weight loss due to corrosion of both WR and EBM alloys. The EBM sample showed a lower corrosion rate by weight loss after 3 weeks; however, weight gain was observed after 6 and 14 weeks of immersion for both WR and EBM samples. Overall, microstructural characterization and electrochemical measurements confirmed the better corrosion behaviour and passive film properties for the EBM alloy in Ringer’s physiological solution at body temperature (37±1 °C).
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