The Role of Coincident Site Lattice Sigma-3 Grain Boundaries in the Crevice Corrosion Resistance of Alloy-22

Alloy-22 electrodes crevice corroded under constant current conditions in 5 M NaCl at 120°C accumulated damage predominantly at the grain boundaries.  Confocal laser scanning microscopy was used to image and quantify the corrosion damage.  The relationship between the locations of damage and the crystallographic features of the alloy was determined by electron backscatter diffraction (EBSD).  EBSD data were used to evaluate the degree of misalignment between adjacent grains in terms of the coincident site lattice concept.  The alloy possesses an exceptionally high number of ‘special’ (Σ3) grain boundaries.  Intergranular attack was observed on grain boundaries not exhibiting this ‘special’ grain boundary character.  The high percentage of low Σ-value grain boundaries probably contributes to the excellent crevice corrosion resistance of this alloy.