Studies of Passive Films on Friction Stir Processed and Laser Peened NiAl Bronze

The friction stir processing and welding of nickel aluminum bronze is used for a variety of naval applications, with laser peening being used as a method for stress mitigation. Such processing has a dramatic effect on both the microstructure of this alloy, as well as on the integrity of the passive film formed in chloride electrolytes, including natural seawater. In addition to using a variety of characterization techniques to determine the effects of friction stir processing on microstructure, including electron microscopy with focused ion beam milling, we have used cyclic polarization, linear polarization, and electrochemical impedance spectroscopy to develop an understanding of passive film behavior for this material in the as-received state, as well as after friction stir processing and laser peening. A variety of impedance models have been explored for fitting the data, including transmission line models. Results on this important alloy, before and after processing will be presented.