Nanoscale Intergranular Corrosion and Relation With Grain Boundary Character as Studied In Situ on Copper

TL;DR

This study investigates how different grain boundary types in copper influence nanoscale intergranular corrosion initiation, using in situ electrochemical microscopy and microstructural analysis to reveal the dependence on boundary character.

Contribution

It introduces an innovative methodology combining ECSTM and EBSD with micro marking to analyze corrosion at specific grain boundaries in copper.

Findings

Random high angle and sigma9 boundaries are susceptible to corrosion.

Sigma3 twin boundaries show resistance or susceptibility depending on deviation angle.

Corrosion initiation is highly dependent on grain boundary character and misorientation.

Abstract

The initiation of intergranular corrosion at various types of grain boundaries (GBs) was studied at the nanometer scale on microcrystalline copper in 1 mM HCl aqueous solution. In situ Electrochemical Scanning Tunneling Microscopy (ECSTM) and Electron Back-Scatter Diffraction analysis of the same local microstructural region were combined using an innovative methodology including micro marking performed with the STM tip. The results demonstrate that electrochemically-induced intergranular dissolution, at the surface termination of GBs, is dependent on the grain boundary character. It is found that random high angle boundaries as well as sigma9 coincidence site lattice (CSL) boundaries are susceptible to nanoscale initiation of intergranular corrosion while for sigma3 CSL boundaries the behavior is dependent on the deviation angle of the GB plane from the exact orientation. For the sigma3 twins, a transition from resistance to susceptibility occurs between 1{\deg} and 1.7{\deg} of deviation as a result of the increase of the density of steps (i.e. misorientation dislocations) in the coincidence boundary plane. The work emphasizes the precision needed in the design of the grain boundary network in applications where intergranular corrosion or its initiation must be controlled at the nanoscale.