Mechanism of the Acceleration of the Electrodic Dissolution of Metals during Yielding under Stress

Abstract

The effect of strain, in particular the effect of varying the rate of its application, both in the elastic and the plastic region, on the anodic dissolution kinetics of several metals has been studied. It has been found in the case of iron in acid solution that the over-all effect of elastic strain is small (i.e., the shift of corrosion potential is about +0.1 mV/1000 kg cm−2) and is mostly due to the change in the rate of hydrogen evolution. The effect of yielding on the rate of the electrodic dissolution of metals (Fe, Mo, Ni, and Cu) has been found to be much more pronounced than that of the elastic deformation. The dissolution rate undergoes a marked rise at the beginning of the plastic region, when straining is carried out at a constant rate, and then shows an asymptotic tendency with increasing strain. The asymptotic values of the anodic current dissolution (c.d.) reached at high values of strain increase linearly with the rate of straining. The slope of this linear relationship increases with increasing anodic potential. Metals which develop high-index planes (h.i.p.) as surface steps upon slipping [e.g., Fe—(112) and (123), Mo—(112)], should give much larger mechano-electrochemical effect in comparison with those which develop only low-index planes (l.i.p.) [e.g., Ni and Cu—(111)],and this should depend on the rate of straining. Some effect found in the l.i.p.-developing metals could be ascribed to increased dissolution rate at slip edges and to increasing surface roughness upon slipping. The rate of metal dissolution on h.i.p. is 50 times larger than that at l.i.p., while the rate of the dissolution at slip edges is about 10 times larger than that at the unstrained metal.

Mechano-electrochemical modelling of corroded steel structures

“…Under external load, it has been generally agreed that the plastic strain will significantly reduce the corrosion resistance by directly enhancing the anodic reaction [7,11,14,16,[21][22][23][24][25][26] while the hydrogen evolution was reported to increase as well [21,22]. Despic et al [11] observed that a negative corrosion potential shifted by up to 30 times, with a marked increase in the anodic current density at the onset of the tensile plastic strain and reached an asymptotic value gradually. Plastic deformation was believed to increase the surface reactivity non-uniformly [26] and the stored energy within a material, which can be directly related to the electrode potential change [27].…”

“…Previous studies have focused on stress corrosion cracking [6,7], corrosion fatigue [8][9][10] and hydrogen-induced cracking [11][12][13] and erosion-corrosion [14][15][16]. It has been reported that 23-33% of the low-alloy steel weight loss was attributed to the mechano-electrochemical effects, while the number could be 55-62% for austenitic stainless steels [17].…”

“…An early study carried out by Despic et al [11] in 1968 reported that during corrosion, only the rate of hydrogen evolution was affected by tensile elastic stress. The chemical potential (the partial molar free Gibbs energy of a substance) of hydrogen was believed to decrease under stress, which lowered the activation energy barrier for hydrogen-metal discharge and hence enhanced the cathodic reaction.…”

Influence d'un état mécanique sur la réactivité de surface en milieux aqueux des métaux c.f.c.

“…Par conséquent, il semble important d'identifier l'influence du comportement élasto-plastique des métaux sur les cinétiques électrochimiques liées aux processus de corrosion (adsorption, dissolution, passivation). Dans le cas particulier des processus de dissolution, quelques études de traction in-situ en milieux acides ont montré une augmentation de la densité de courant puis une diminution de celle-ci lorsque la déformation plastique augmente [9,[11][12][13][14][15]. Ce résultat important peut être interprété de multiples façons : une augmentation de l'activité de la dissolution sur les marches associées à l'émergence des lignes de glissement, une augmentation de la rugosité, une réduction des distances de diffusion en surface, une modification de l'entropie du système associée à la présence de dislocations et d'un état de contrainte, .…”

“…. [11,12]. Les tentatives d'interprétation des résultats in-situ ne distinguent que rarement les effets de la contrainte de ceux des défauts développés par la plasticité.…”