Corrosion Susceptibility and Functionally Graded Properties of Ti-35Nb-4Sn Alloy Processed by Laser Remelting

The effect of laser remelting on the corrosion susceptibility and mechanical properties of Ti-35Nb-4Sn (mass%) alloy is investigated across the remelted track profile. In comparison to the cold-rolled microstructure of base metal, recrystallization of heat affected zone (HAZ) improved plastic energy absorption and pitting corrosion resistance, by the reduction of active sites for pit nucleation. In fusion zone, however, passivation was compromised by the formation of dendritic microstructure with Sn enriched interdendritic region, where preferential pitting corrosion occurred. Fusion zone was the most anodic region and presented a corrosion potential difference of 35 mV, in comparison to the adjacent and most cathodic HAZ. Electrochemical impedance analysis showed that spontaneous passivation was most effective in base metal, that developed a thicker and more compact passive film. Local increase in elastic modulus and microhardness of fusion zone shows that laser remelting is a viable processing route for the manufacturing of biomaterials with functionally graded properties.