Influence of Crack Tip Plasticity on the Microstructure and Corrosion Behavior of CA6NM Stainless Steel Measured Using Scanning Electrochemical Cell Microscopy (SECCM)

Abstract

The existence of cracks within ductile materials such as stainless steel induces local plasticity around the crack tip that may cause local changes in the microstructure. Although the plastic deformation and microstructural heterogeneities are expected to influence the electrochemistry of the area around the crack tip, few are the studies that correlate the factors- strain and corrosion- together.In this work, we analyze the corrosion behavior of pre-cracked CA6NM compact tension stainless steel samples taking into consideration the variations in the microstructure resulting from the local plasticity at the tip of a crack. Multiple surface microstructure analysis are obtained to characterize the surface properties of the plastic zone. The localized corrosion behavior around the crack tip is studied using the scanning electrochemical cell microscopy (SECCM) technique. The acquired micro open circuit potential (OCP) and micro potentiodynamic polarization (PDP) curves were used to generate corrosion potential and corrosion current maps of the scanned area. The electrochemical behavior of the crack tip was compared with that in the un-deformed area of the same sample.The ability to conduct direct electrochemical measurements at microscopic scale through SECCM allows to correlate the localized corrosion behavior to the microstructure analysis obtained before. This work paves the avenue to studying the synergistic effect of fatigue damage on the local corrosion behavior through monitoring both simultaneously.