The Relation between Irradiation Assisted Stress Corrosion Cracking and Dislocation Channeling: The Role of Slip Interaction at the Grain Boundary.

Abstract

The objective of this study was to determine the role of localized deformation in irradiation assisted stress corrosion cracking. First, the character of grain boundaries susceptible to cracking was examined. It was observed that boundaries intersected by discontinuous dislocation channels were more susceptible to cracking. Channels were then characterized based on their interactions with the grain boundary, and cracking susceptibility was examined based on these channel-boundary classifications. Results show that dislocation channels are connected to irradiation assisted stress corrosion cracking, however, the mechanism connecting the two is still unknown Grain boundary susceptibility to cracking was characterized based on boundary misorientation, angle with respect to the tensile axis, Schmid Factor, Taylor Factor, and the continuity of the channels intersecting the boundary. It was found that cracking propensity was higher at random high angle boundaries, boundaries normal to the tensile axis, boundaries adjacent to low Schmid Factor or High Taylor factor grains and boundaries that were intersected by discontinuous channels. Digital image correlation and confocal microscopy were used to characterize the channels, with the focus being at the channel-boundary intersection. Channels either were transmitted across the grain boundary and classified as continuous, were discontinuous and terminated at the grain boundary (discontinuous), or were discontinuous at the grain boundary but induced grain boundary slip (discontinuous with grain boundary slip). Continuous channels were found to undergo the largest amount of slip, while discontinuous channels underwent the least. Despite the low amount of slip within the discontinuous channels, these were found to be the most likely to induce cracking. This is believed to be caused by the high level of stress that results from the unaccommodated slip. Other areas of high stress, such as triple junctions, were also found to be susceptible to cracking. This work was able determine the relative amounts of cracking occurring from discontinuous channels that induced grain boundary slip and those that resulted in dislocation pile-ups at the grain boundaries. The findings of this work indicate that the localized deformation in irradiated austenitic stainless steel causes areas of unaccommodated slip which results in high stress, and leads to IASCC.