A 4-electrode analogue for estimating electrochemical reactions with bare metal surfaces at the crack tip

Abstract

Summary A 4-electrode in situ fracture technique has been developed as an analogue for estimating, under potentiostatic control, the kinetics of electrochemical reactions with a bare metal surface which is coupled to an “oxidized” surface of the same material. The technique simulates the equilibration reactions that occur at the tip of a growing crack. The relevance and effectiveness of this technique have been demonstrated by the good correlation between independently measured charge transfer data and corrosion fatigue crack growth rate data obtained under an externally applied cathodic potential. The results suggest that the electrode potential at the crack tip does not deviate substantially from the free corrosion potential. With the aid of this technique, a consistent and quantifiable picture of the role of electrochemical reactions in corrosion fatigue crack growth is beginning to emerge. Further quantitative understanding of corrosion fatigue crack growth of steels in aqueous environments is now possible, and is being fully explored.