Interaction between Dislocation Sliding and Damage Structure in Ion-irradiated Stainless Steels
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Interaction between Dislocation Sliding and Damage Structure in Ion-irradiated Stainless Steels Terumitsu Miura, Katsuhiko Fujii, and Koji Fukuya Institute of Nuclear Safety System, Incorporated, Fukui, Japan ABSTRACT The interaction between dislocation sliding and damage structure in ion-irradiated austenitic stainless steels was investigated. Solution annealed type 316 and 304 stainless steels (316SS and 304SS) were irradiated with 2.8 MeV Fe2+ ions at 300 °C up to 10 dpa and tensiled to 2% plastic strain at 300 °C. Dislocations moving from unirradiated matrix were prevented due to the interactions with the damage structures consisted of dislocation loops and voids in the damage region. The prevention of dislocation movements by the damage structures became strong in 304SS compared in 316SS; probably due to lower stacking fault energy in 304SS. The prevention of dislocation movements was weak for Fe ion-irradiated specimens in which the increase in shear strength calculated from the size and number density of the defects was small compared to He ion-irradiated specimens.
INTRODUCTION The deformation behavior of irradiated austenitic stainless steels has been well examined. However, the study is limited about the deformation behavior at light water reactor temperatures that has been recently suggested the relation to the mechanism of occurrence and propagation of irradiation assisted stress corrosion cracking [1]. It has been reported that deformation was localized to dislocation channels in neutron irradiated stainless steels and twinning was favored at several conditions such as low temperatures, high strain rates and highly irradiated conditions [2-4]. The deformation behavior has also been investigated using ion- and proton-irradiated stainless steels because irradiation conditions are limited for neutron irradiation and it is difficult to perform a number of experiments using radioactivated specimens [5-7]. We have used ion-irradiation to investigate the relationship between the deformation behavior in ionirradiated stainless steels and the nature of damage structure that is kind, size and number density of defects constituting the damage structure because the ion-irradiation could control the nature of damage structure widely. In this study, the interaction between dislocation sliding and the damage structures was investigated using Fe irradiated stainless steels. The relationship between the deformation behavior and the nature of damage structures was also discussed together with the previous experimental results using He irradiation [8].
EXPERIMENT Solution annealed type 316 and 304 stainless steels (316SS and 304SS) with average grain sizes of 40 and 85 µm, respectively, were used. The chemical compositions are shown in Table I. Small flat tensile specimens with the gage section of 9×3×1 mm were prepared from the steels. The surfaces were polished mechanically and electrolytically. One side of the gage section
316SS 304SS
Table I. Chemical compositions of 316SS and 304SS (wt%). C Si Mn P
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