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The effect of partial replacement of nickel with nitrogen on the corrosion resistance of newly designed austenitic stainless steel samples without and with heat treated was investigated in 3.5wt% and 5wt% NaCl solution using open-circuit, potentiodynamic, cyclic anodic polarization and electrochemical impedance spectroscopy techniques. The results showed that, passivation in sample 1 where the highest addition of nickel and low addition of nitrogen is different from that for sample 4 where the nitrogen is greatest and the nickel is reduced almost to the third comparing sample 1. The difference in responses of heat treated samples to localized and general corrosion could be attributed to the difference in their phase compositions. The appearance of ferrite phase for samples (2, 4, 5 and 6) after heat treatment resulted in lowering the general and localized corrosion resistance than as forged samples in contrast with samples 1 and 3, where they still pure austenite. The obtained results are confirmed by surface examination.

C OPPER-NICKEL alloy is a material of choice for condensers and heat exchangers, where seawater is used as a coolant and in desalination plants. In this work, we survey the comparative corroding behavior of novel designs of 90/10 and 70/30 Copper-Nickel alloys under higher salinity (3.5 wt%, 10 wt% and 15 wt% NaCl). The electrochemical corrosion of Cu-Ni alloys in brine solutions was studied using potentiodynamic polarization, chronoamperometric and electrochemical impedance spectroscopy measurements along with scanning electron microscope (SEM) and energy dispersive X-Ray analyzer (EDX) investigations. Polarization data showed that Cu-10 Ni alloy is more corrosive than Cu-30 Ni alloy in 3.5 wt% NaCl solutions. Chronoamperometric curves confirmed the results obtained by polarization measurements that the uniform and pitting corrosion of Cu-Ni alloy were reduced in the Cu-30 Ni alloy in 3.5wt% NaCl solutions. Impedance spectra revealed that the surface and polarization resistances recorded higher values in Cu-30Ni alloy. SEM/EDX investigations indicated that the corrosion of Cu-Ni alloys proceeded by the selective electro-dissolution of nickel, which allowed copper enrichment on the surface of the alloy. The heat exchanger served to heat desalinated water, the water had a high chloride level. Corrosion examination indicated susceptibility towards pitting corrosion, especially at high temperature.

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