The Research Of Micro-defects Capturing Hydrogen/Helium In Reduced Activation Ferritic/Martensitic Steels

Reduced activation ferritic/martensitic(RAFM) steels are promising structural materials for the future nuclear fusion reactors since they have the advantages of low activation, excellent void swelling resistance and adequate mechanical properties. However, displacement damage caused by 14 MeV neutron irradiation, hydrogen and helium effect would lead to the changes of the microstructure and mechanical property, especially the increment of the ductile-to-brittle transition temperature. Therefore, it is need to do the research of micro-defects capturing hydrogen and helium in this steel. Low activation ferritic/martensitic steels are based on Fe9 Cr. Thus, the Fe9 Cr alloy will be investigated in this project. The micro-defects will be produced by cold rolling deformation and ion irradiation, and then the hydrogen and helium atoms will be also introduced by ion implanter. The research of micro-defects capturing hydrogen and helium in RAFM and Fe9 Cr alloy would be investigated by Transmission electron microscope, Positron annihilation technique and Thermal desorption spectroscopy.1?3 keV He ion irradiation could introduce the vacancy and dislocation defect. The cold rolling deformation could also induce the mainly dislocation defects. These defects, acted as the trapping sites, could capture the helium atoms. Helium thermal desorption peaks from dislocations, helium-vacancies were obtained by TDS at ~ 540 oC, in the range from 205 oC to 478 oC, respectively. According the relation between defects and desorption temperature, the desorption energies of helium atoms from defects were estimated and analyzed. The phase transition for alpha-gamma(BCC-FCC) in Fe9 Cr alloy would release the helium atoms, and the desorption temperature was about at 865 oC. High thermally stable HenD type complexes formed in Fe9 Cr alloy by deformation,resulting in the retardation of gas migrate or release. Implantation of hydrogen into the specimens pre-irradiated by helium can result in obvious enhancement of clusters size and retardation of helium release which can be regarded as a consequence of hydrogen being trapped by HenVm type complexes.2?The defect profiles in RAFM steel irradiated with 250 keV He ions and 130 keV H ions at 450 oC were observed by PAS. Slow positron beam study revealed that single ions(He or H) implanted into RAFM steel would combine with vacancies and form(He or H)-V clusters. Hen Vm clusters were more likely to grow by thermal activating, and formed overpressured HenVm clusters. The synergistic effect of post-irradiation of H ions on HenVm clusters was to help them turn into He-H-V clusters, which were in higher pressure.3?Coincidence Doppler broadening spectroscopy of slow positron annihilation was employed to detect He atoms in ion irradiated Fe9 Cr alloys. Spectra with higher peak to background ratio were recorded using a two-HPGe-detector coincidence system. It is shown that features in the high-momentum region of the spectra can be used to identify helium element in metals. This result is perhaps surprising since one would expect the detailed shape of the annihilation spectrum to be dependent on the structure and microscopic arrangement of atoms surrounding the annihilation site. The results of Doppler broadening spectroscopy and transmission electron microscopy show that vacancies and dislocations were formed in ion irradiated specimens. Thermal helium desorption spectrometry was performed to obtain the types of He traps.