Passivation of laser-treated nickel aluminum bronze as measured by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy was used to assess the corrosion beh avior of the weld zones and surface conditions of a laser-clad nickel alumi num bronze immersed in a 3.5% neutral saline solution. The zones and condit ions examined included: (i) as-cast base material; (ii) laser-clad material with the high temperature oxide from welding intact; (iii) polished laser- clad material and (iv) specimens representative of just the as-deposited an d reheated zones of the laser-clad surface. A pseudo steady-state level of passivation was reached in all the samples within 40 hours. The reheated zo ne passivated more slowly than the as-deposited region and both weld zones passivated more quickly than the base material. Electrochemical impedance d ata illustrated a transition during the passivation process of the polished specimens that is consistent with the development of a film layer that res tricted mass transfer. The welding oxide from the laser treatment immediate ly behaved as a passivation film that was indistinguishable from that which eventually develops on polished specimens.