Micro-electrochemical evaluation of α- Or β-type titanium alloys

In order to evaluate electrochemical stabilities of α, β phases, the micro-electrode techniques was employed to test the micropolarization behavior of α-type pure Ti and β-type Ti15Mo alloys. The comparison between macropolarization and micropolarization curves demonstrates that the α-type pure Ti alloy tends to exhibit the uniform corrosion, on the other hand, the pitting corrosion is the main form for the β-type Ti15Mo alloys. The α grains with different orientations shows similar polarization behavior, but the polarization behavior of those β grains are strongly affected by their crystalline orientations, particularly the worse electrochemical stabilities of β grains with (200)-dominance. The corrosion potential and corrosion current density of α-type pure Ti is lower than β-type Ti15Mo alloys. The α grains have better electrochemical stabilities in comparison to β grains, which indicate that the α+β dual-phase Ti-6Al-4V ELI alloys is highly possible to suffer from the preferential dissolution of β grains in free immersion condition and/or polarized states. Finally, by combining the SEM, EDS and polarization curves of dual-phase Ti-6Al-4V ELI alloys, it is concluded that β phases are corroded prior to α phases.