Corrosion Behavior of High-Nickel and Chromium Alloys in Natural Baltic Seawater

Effect of Cl^– ion concentration (0 M sodium chloride [NaCl] to 2 M NaCl) and temperature (25°C to 75°C) on stability of the passive state of high-Ni and Cr alloys: NI-1 (~ 16% Mo), CR-2 (~ 6.2% Mo), and NI-3 (3.5% Mo) were investigated in acidic and neutral electrolytes in strictly controlled electrochemical conditions. The anodic behavior of the alloys appeared to depend mostly upon Mo content in the alloy. Thus, the NI-1 was the most stable alloy under the applied experimental conditions. The other alloys were also quite resistant, undergoing pitting only at elevated temperatures, at high anodic potentials, and at a chloride concentration not lower than 1 M. In natural Baltic seawater, these alloys did not exhibit any tendency to pitting, in qualitative agreement with the accelerated electrochemical tests. Complementary microscopic and surface analytical (AES) investigations were carried out to correlate the anodic and corrosion behavior of these materials with their composition and structure, and the composition of the passivating films formed at their surfaces.