Excimer laser surface treatment of Ti-6Al-4V alloy for corrosion resistance enhancement

Excimer laser surface treatment of Ti-6Al-4V alloy was conducted with the aim of improving the pitting corrosion resistance of the alloy. Laser surface treatment was performed under two different gas environments, argon and nitrogen. The microstructure, phase and composition of the modified surface structure were analysed using TEM, XRD and EDX; the electrochemical behaviours of the untreated and the laser-treated specimens were evaluated by electrochemical polarization tests. Excimer laser surface treatment significantly increased the pitting potential of the Ti alloy, especially when the material was treated in argon gas, while a seven-fold reduction in corrosion current was obtained when the material was treated in nitrogen gas. These improvements are considered to be primarily due to the reduction of solute partitioning effect of detrimental Al segregated to the α phase. The N2-treated specimen, although it had the lowest corrosion current, had a pitting potential some 100 m V lower than that of the Ar-treated specimen. This is considered to be due to TiN precipitates acting as galvanic cathodes at high corrosion potentials.