Effect of Tensile Stress on the Passivity Breakdown and Repassivation of AISI 304 Stainless Steel: A Scanning Kelvin Probe and Scanning Electrochemical Microscopy Study

The interplay between mechanical stresses and electrochemical reactions may lead to stress corrosion cracking or hydrogen embrittlement for many materials. In this work, the effect of the tensile stress on the electrochemical properties of AISI 304 stainless steel was studied using scanning Kelvin probe (SKP) in air and scanning electrochemical microscopy (SECM) in an aqueous 0.5 M Na2SO4 electrolyte. The measurements were performed under load- and load- free conditions. No influence of the elastic stress on the electrochemical potential of the steel was found. In contrast, the plastic strain induces dislocations and dislocation pile-ups, which emerge to the surface. The formation of new active surfaces is accompanied by an increase in the roughness and a 150-200 mV decrease in the steel potential. After activation, the potential increased due to passivation of the emerging surfaces by a newly grown oxide film, which took place under both the load and load- free conditions and followed a time dependence of phi = A log t + B. Formation and then passivation of the new surfaces increased and then decreased the reduction current of the mediator in the SECM measurements. The effect of residual stress stored in the steel due to the development of dislocations on the reactivity of the re-passivated surface was investigated. (c) The Author(s) 2019. Published by ECS.