Flaw of Electrolyte within a Propagating Stress-Corrosion Crack

Abstract

THE observed corrosion potential at the mouth of a propagating crack in stressed Cu₃Au immersed in FeCl₃ is as much as 0.1 V, negative relative to that at uncracked parts of the surface¹. This suggests that the advancing crack edge is dissolving anodically at an even lower potential. Potential measurements on stress-corroding wires of 18–8 steel in hot magnesium chloride solution^2,3, where the average corrosion potential during cracking is only about 0.06 V. above the reversible potential, suggest further that the potential at the advancing edges must in fact be very close to the reversible value. This led Hoar and West⁴ to study the electrochemistry of 18–8 surfaces made to represent, on a macroscopic scale, the yielding material at such edges. Their experiments showed that dissolution of yielding 18–8 proceeds at the reversible potential provided that concentration over-potential is eliminated by flowing electrolyte past the surface at a suitable rate. It may be inferred that the advancing edge of a propagating stress-corrosion crack dissolves continuously into substantially virgin electrolyte, in view of the concomitant yawning.