Electrochemical Surface Nanostructuring of Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 Metallic Glass for Improved Pitting Corrosion Resistance

Ti-based bulk metallic glasses are envisioned for human implant applications. Yet, while their elevated Cu content is essential for a high glass-forming ability, it poses biocompatibility issues, necessitating a reduction in near-surface regions. To address this, surface treatments that simultaneously generate protective and bioactive states, based on nanostructured Ti and Zr-oxide layers are proposed. An electrochemical pseudo-dealloying process using the bulk glass-forming Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 alloy is defined. Melt-spun ribbons are immersed in hot concentrated nitric acid solution, monitoring the anodic polarization behavior. From the current density transient measurements, together with surface studies (field-emission scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy), the surface reactions are described. This nanostructuring process is divided into three stages: passivation, Cu dissolution, and slow oxide growth, leading to homogenous nanoporous and ligament structures. By tuning the applied potential, the pore and ligament sizes, and thickness values are adjusted. According to X-ray photoelectron spectroscopy, these nanoporous structures are Ti and Zr-oxides rich in hydrous and nonhydrous states. In a simulated physiological solution, for those treated glassy alloy samples, complete suppression of chloride-induced pitting corrosion in the anodic regime of water stability is achieved. This high corrosion resistance is similar to that of clinically used cp-Ti.