Effect of pre-implanted helium on cavity formation in modified 316 stainless steels during electron irradiation

Cavity formation and dislocation structural evolution during electron irradiation were investigated in modified 316 stainless steels implanted by helium. In standard 316 steel, helium implantation caused to increase in cavity number density and reduced the size at whole temperature range of 623 to 873 K. However, implanted helium in Si and Ti-modified steels enhanced strongly the cavity nucleation at lower temperature, and suppressed cavity formation at higher temeprature. Moreover, initial dislocation structure was also affected by the helium. Especially black dots were observed with high density and not changed with further irradiation eventhough at higher temperature. From these results it is suggested that helium could affect on the both of dislocation loop and cavity formation, and the suppression effect of helium on cavity formation would originate from the loops of high number density, in which they would act as a neutral sink for point defects. (orig./RK)