Mechanism of dislocation channel-induced irradiation assisted stress corrosion crack initiation in austenitic stainless steel

Abstract

The mechanism by which dislocation channeling induces irradiation assisted stress corrosion cracking was determined using Fe-13Cr15Ni austenitic stainless steel irradiated with protons to a dose of 5 dpa and strained at high temperature in both argon and simulated boiling water reactor normal water chemistry environments. Straining induced dislocation channels that were characterized by digital image correlation and confocal microscopy. Dislocation channels were found to be either continuous across the boundary, discontinuous, or discontinuous with slip in the boundary. Discontinuous channels were found to contain the least amount of strain but have the highest propensity for initiating cracks. Discontinuous dislocation channel-grain boundary intersections were shown to have the highest local stress. TEM in-situ straining of irradiated steels and atomistic simulation of dislocation-grain boundary interaction provided supporting evidence that channels that were unable to transfer strain underwent cracking. The inability of channels to relieve stress, by either slip in the adjacent grain or in the grain boundary, resulted in high local stresses and increased susceptibility to stress corrosion cracking initiation.

Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel

“…Numerous studies have been conducted in the recent past on IGSCC of (ion-irradiated) austenitic stainless steel, mainly with applied stress well above yield stress. It has been shown (see, e.g., [38]) that dislocation channelling (or clear bands) resulting in strain localization at the grain scale may be a factor controlling IGSCC of irradiated stainless steel. The constitutive equations used in this study do not display instabilities and subsequent strong strain localization at the grain scale, and therefore the results and methodology proposed in this study would probably show limitations when applied to highly strained materials.…”

Intergranular normal stress distributions in untextured polycrystalline aggregates

“…Various physical mechanisms have been proposed to explain IGSCC (Burleigh, 1991)e.g. active path dissolution (Parkins, 1980), slip-dissolution (Newman and Healey, 2007), hydrogen embrittlement (Beachem, 1972), localized deformation (Bieler et al, 2009;McMurtrey et al, 2015) -that depend on the material, the corrosive environment and the local stress state. As such, evaluation of intergranular stresses is required in order to quantitatively predict IGSCC.…”

“…As such, evaluation of intergranular stresses is required in order to quantitatively predict IGSCC. In the recent years, experimental assessment of grain boundaries stresses has become available through High Resolution Electron Back Scatter Diffraction (HR EBSD) (Gardner et al, 2010;McMurtrey et al, 2015) or Laue microdiffraction (Larson et al, 2002;Guo et al, 2015) which remains up to now limited to rather small number of grain boundaries and therefore does not allow to get statistical information about intergranular stress distributions.…”

Evaluation of stress corrosion cracking of irradiated 304L stainless steel in PWR environment using heavy ion irradiation

“…[18] based on Slow Strain Rate tensile (SSRT) tests in a BWR environment. In addition, this study proposed that a certain amount of localized deformation is necessary to obtain Inter-Granular Stress Corrosion Cracking (IGSCC), which is related to the surface oxide film breakage either by grain boundary sliding [17] or by the high local stresses induced locally by dislocation channel-grain boundary interactions [19].…”