Use of Electrochemical Hystersis Techniques in Developing Alloys for Saline Exposures^*

Electrochemical hysteresis techniques may be used to construct experimental potential versus pH diagrams for alloy systems. Examples presented include binary alloys of the Fe-Cr and Cu-Ni systems. Such diagrams are a valuable alloy development tool since they provide a basis for comparison of the corrosion behavior of several alloys in a family of alloys. It is also possible to present relative corrosion rates for the alloys as iso-corrosion contours on pH versus potential coordinates. The influence of variation in chloride ion activity on the corrosion behavior of Fe-Cr alloys is expressed in terms of influence on zero current potentials, passivation potentials, protection potentials, and rupture (pitting) potentials. From an engineering standpoint, the protection potential appears to offer certain advantages over the pitting potential for the Fe-Cr alloys.