Microstructure and Corrosion Behavior of Laser-Remelted Ti-35Nb(-Sn) Alloys

Ti-35Nb-Sn alloys are being investigated for biomedical applications as hard tissue replacements due to their reduced elastic modulus, which is closer to that of natural bone, and helping to minimize stress shielding and bone resorption. Laser remelting is a promising processing route for the manufacture of implants with a graded elastic modulus and optimized performance. This study investigates the impact of laser processing on the microstructure and corrosion resistance of Ti-35Nb alloys containing 0, 2, and 4 wt.% Sn. Microstructural morphology, chemical composition, and phase formation were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and x-ray diffraction (XRD), respectively. Corrosion resistance of the alloys was assessed in the base metal, heat-affected zone (HAZ), and fusion zone (FZ) using linear polarization tests in a physiological saline solution, using a three-electrode setup and an in-house developed microcell with a mask to limit the exposed area. Laser processing increased the fraction of the β phase in the alloys through reversion of strain-induced α ″ martensite and through elemental partitioning in the fusion zone, where Nb enrichment stabilized the β phase in dendrite cores. Under the tested conditions, laser processing did not seem to degrade the corrosion performance of Ti-35Nb and Ti-35Nb-2Sn, maintaining or shifting E corr and E pit to more noble values with similar or slightly reduced corrosion current densities. In contrast, the addition of 4 wt.% Sn had a detrimental effect, shifting E corr and E pit to more negative values, reducing polarization resistance, and increasing corrosion current densities by up to 10 × . In this alloy, laser processing promoted elemental segregation in the fusion zone, favoring localized corrosion in Sn-rich interdendritic regions. This work provides a deeper understanding of the relationships between laser processing, microstructure, and corrosion performance in laser-treated niobium-stabilized β-titanium alloys.