Chloride Ion Concentration and pH Dependence of the Transient Dissolution Characteristics of Metals During High Strain Corrosion Fatigue

The cyclic strain enhanced electrochemical reactions on mild steel have been examined in aqueous solutions containing 0.04% to 20% NaCl in the pH range 1 to 14. Current transients were generated in all solutions during both the tensile and compressive strain reversals. The magnitude of the dissolution transients depended to a large extent on the chloride ion concentration, the pH of the solution, the test potential, and the number of prior strain cycles to which the material was subjected. The major effects of increasing chloride ion concentration were found in the pH range 3 to 14, where films are known to exist on the metal surface whereas, in the acidic media, the dissolution behavior of the metal was not significantly influenced. Analysis of the dissolution and film formation kinetics revealed that the principle involvement of chloride ions was associated with their effect on film stability rather than an inherent influence facilitating dissolution of the metal ions from a film free surface.