TEM Observation of Loops Decorating Dislocations and Resulting Source Hardening of Neutron-Irradiated Fe-Cr Alloys

Frank Bergner (1) , Mercedes Hernández-Mayoral (2) , Cornelia Heintze (1) , Milan J Konstantinović (3) , Lorenzo Malerba (2) , Cristelle Pareige (4)

1 HZDR - Helmholtz-Zentrum Dresden-Rossendorf
2 CIEMAT - Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
3 SCK-CEN - Centre d'Etude de l'Energie Nucléaire
4 GPM - Groupe de physique des matériaux

Several open issues remain concerning the quantitative understanding of irradiation hardening in high-Cr steels. One of these issues is addressed here by correlating yield points that are observed in stress-strain curves with dislocation decoration observed by TEM for neutron-irradiated Fe-Cr alloys. It is found that both higher neutron exposure and higher Cr content promote irradiation-induced loops to arrange preferentially along dislocation lines. Consequently, the activation of dislocation sources requires unlocking from the decorating loops, thus resulting in a yield drop. This process is considered within the source hardening model as opposed to the dispersed barrier hardening model, the latter aimed to describe dislocation slip through a random array of obstacles. Microstructure-informed estimates of the unlocking stress are compared with measured values of the upper yield stress. As functions of neutron exposure, a cross-over from the dominance of dispersed-barrier hardening accompanied by smooth elastic-plastic transitions to the dominance of source hardening accompanied by yield drops is observed for Fe-9% Cr and Fe-12% Cr.

Mots clés: hardening; neutron irradiation; TEM; tensile test; iron-chromium alloy; dislocation loop

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Frank Bergner, Mercedes Hernández-Mayoral, Cornelia Heintze, Milan J Konstantinović, Lorenzo Malerba, et al.. TEM Observation of Loops Decorating Dislocations and Resulting Source Hardening of Neutron-Irradiated Fe-Cr Alloys. Metals, 2020, 10, ⟨10.3390/met10010147⟩. ⟨hal-02444695⟩