The effect of dislocation channel on intergranular microcrack nucleation during the tensile deformation of pre-irradiated austenitic stainless steels was studied. Because several slip planes were activated within the dislocation channel, the simple dislocation pile-up model seems not well suited to predict grain boundary stress field. Finite element computations, using crystal plasticity laws and meshes including a channel of finite thickness, were also performed in order to study the effect of some microstructural characteristics on grain boundary stress field. Numerical results showed that: the thickness and the length of the dislocation channel strongly influenced the grain boundary normal stress field. The grain boundary orientation with respect the stress axis did not affect so much the grain boundary normal stresses close to the dislocation channel. On the contrary, far away the dislocation channel, the grain boundary stress field depends on the grain boundary orientation. Based on these numerical results, an analytical model was proposed to predict grain boundary stress fields. It was valuable for large ranges of dislocation channel thickness, length as well as applied stress. Then, a macroscopic microcrack nucleation criterion was deduced based on the elastic–brittle Griffith model. The proposed criterion predicts correctly the influence of grain boundary characteristics (low-angle boundaries, non-coincident site lattice high-angle boundaries, special grain boundaries) on intergranular microcrack nucleation and the macroscopic tensile stress required for grain boundary microcrack nucleation for pre-irradiated austenitic stainless steels deformed in argon environment. The criterion based on a dislocation pile-up model (Smith & Barnby) underestimates strongly the nucleation stress. These results confirmed that pile-up models were not well suited to predict microcrack nucleation stress in the case of dislocation channels impacting grain boundary. The proposed criterion was applied to the prediction of the macroscopic nucleation stress for pre-irradiated material.

Modelling of the Effect of Dislocation Channel on Intergranular Microcrack Nucleation in Pre-Irradiated Austenitic Stainless Steels during Low Strain Rate Tensile Loading. P.Evrard, M.Sauzay: Journal of Nuclear Materials, 2010, 405[2], 83-94