Abstract
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 φ = 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.
Highlights
The passivity and stability of passive oxide films play important roles in the susceptibility of stainless steels to local corrosion phenomena such as pitting and stress corrosion cracking (SCC)
The present study reports the effect of tensile stress on the electrochemical properties of AISI 304 steel surfaces
When the sample was exposed to the load for 5 h, the potential at all points along the sample increased by 20
Summary
The passivity and stability of passive oxide films play important roles in the susceptibility of stainless steels to local corrosion phenomena such as pitting and stress corrosion cracking (SCC). The breakdown of the passive film by either mechanical or chemical factors is one of the important issues in the theory and understanding of SCC. Dissolution model, cracks develop due to cycling processes resulting in successive active film rupture and dissolution and film repassivation processes. The film rupturing occurs due to the application of tensile stress generated by mechanical loading of the bulk of the material [1]. Breakdown of the passive film can result from the migration of dislocations and dislocation pile-ups to the metal surface [2]. The strain rate and the surface repassivation rate inside the crack are key factors in the propagation of SCC [3,4,5,6]. Metallic structures are often working under an elastic stress load. The impact of elastic stress and plastic deformation on electrochemical properties is worth studying in detail
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