Effect of Grain Boundary Inclination on Intergranular Corrosion of Alloy 690 with Coarse Columnar Crystals.

The effect of grain boundary inclination on intergranular corrosion in boi-l ing HNO3+Cr6+ solution was investigated on Alloy 690 with coarse columnar crystals. As the deviation of the growing direction from ‹100› orientation was within 10°, the grain boundaries were treated approximately as simple tilt boundaries with ‹100› rotation axis. The depth of intergraunlar corrosion, h, showed a tendency to increase with increasing the relative tilt angle, ω. At the symmetrical tilt boundaries, h decreased at coincidence boundaries such as Σ13 and Σ17 against the normal relation of h with ω. It was found that grain boundaries of which the planes are close to {100} or {110} of both component crystals have lower susceptibility to corrosion. And at the boundaries with ω which is less than 10°, h was small. The groove angle of intergranular corrosion decreased with increasing h. The groove width of intergranular corrosion on the surface did not depend on h so much.