Influence of grain size on the electrochemical behavior of pure copper

Despite numerous research works a thorough understanding on how grain size influences the electrochemical behavior of metals is still lacking due to the inability to decouple grain size effects from other microstructural characteristics. In this work, the combination of potentiodynamic polarization measurements and the gold-nanoplating technique was used on high purity copper to further explore this relationship. The high purity copper was thermomechanically processed in such a way that three samples were produced with markedly different average grain sizes, namely 1.4, 48 and 191 µm. All other parameters influencing the electrochemical behavior, such as internal stresses and texture were kept constant; microstructural characterization was performed by electron backscatter diffraction. In 0.1 M HCl, the anodic polarization curves demonstrate that for the smaller the grain size a lower corrosion potential and higher corrosion current density is observed. The gold-nanoplating experiments show that the material with the smallest grain size is corroding more uniformly than the samples with the larger grain sizes. In the sample with the medium grain size, the higher electrochemical activity of the grain boundaries is demonstrated. In the largest grain size sample, both the grain boundaries as well as some of the grain interiors are covered with gold.