MICROCHEMICAL AND MICROSTRUCTURAL CHANGES OF AUSTENITIC STEELS CAUSEDBY PROTON IRRADIATION FOLLOWING HELIUM IMPLANTATION

In austenitic steels used for light water reactors, neutron irradiatio n induces the microchemical and microstructural changes in matrices an d around grain boundaries, which are related to various property chang es, such as irradiation hardening and irradiation assisted stress corr osion cracking (IASCC). These phenomena may also be important in fusio n reactors, if austenitic steels are used in core-components. The grai n boundary segregation and the microstructural development depend on i rradiation conditions, such as dpa levels, helium contents and tempera tures, etc, The effects of helium, however, have not yet been clarifie d. This paper presents microchemical and microstructural changes in 30 4SS and XM-19 steel implanted with helium and irradiated with proton. The TEM disks were implanted with helium of 15 appm and irradiated wit h 2 MeV H-2(+) ion to about 1 dpa at 300 degrees C. Chemical analysis was performed using: Field Emission Transmission Electron Microscope ( FE-TEM) and showed that the depletion of chromium at a grain boundary. However, the amount of the depletion strongly depended on both chemic al compositions of the steels and helium contents. Observation by TEM also indicated that small cavities generated in both of the irradiated steels. Nucleation of these cavities may be mainly due to the effects of implanted helium prior to H-2(+) ion irradiation. (C) 1998 Elsevie r Science B.V. All rights reserved.