The Research Of Hydrogrn/Heliun Irradiation Induced Vacancy-Type Defects In Reduced Activation Steels

Low-activated steel,as a candidate structural material for future fusion reactors and fourth-generation reactor technology,has attracted wide attention of researchers including RAFM steels and ODS steels.Nowadays,the effects of hydrogen and cesium-induced embrittlement,defect evolution and macroscopic mechanical properties caused by neutron metamorphosis are the difficulties and hotspots in the study of basic physical problems of structural materials.In this paper,RAFM steel and ODS steel are mainly studied,and Fe-9 wt.% Cr is used as the matrix to refine,and other trace elements such as W,V,C,Ta,Si are added.The introduction of hydrogen and helium atoms herein are accomplished by ion irradiation techniques.Using the methods of positron annihilation,scanning electron microscopy,atomic force microscopy and synchrotron radiation X-ray diffraction analysis,the four methods are combined to give full play to the advantages of each analytical technique,and to study the microscopic generation of radiation in reduced activation steel.Defects,mainly vacancy-type defects,as well as the severity and impact of surface damage caused by bubbles on the surface.In this paper,the radiation damage of irradiated ODS steels with the same energy and different irradiation doses was studied.Different irradiation doses will lead to the occurrence of different types of defects and the number of defects.Conducting the same energy,different irradiation doses of hydrogen irradiation ODS steels and RAFM steels radiation damage study,different materials will produce different irradiation effects under the same irradiation conditions.The results of SRIM simulation calculation and positron annihilation spectroscopy show that the damage range of 170 keV He²⁺irradiated ODS steels is around 600 nm.The positron annihilation lifetime results show that the size of the positron defects generated by the irradiation is relatively small,and the defect type is a vacancy type defect.The slow positron beam Doppler broadening measurement further determined that the high dose He²⁺irradiation is easy to combine with the vacancies,occupying the vacancy to form the He-vacancy complex structure.When the irradiation dose is 1×1016 cm^-2,the number of vacancies formed is the most.The degree of irradiation damage on the surface of the sample was positively correlated with the irradiation dose.Small voids and precipitates were observed.The 5×1016 cm^-2 dose caused the surface wrinkles due to the high implant dose irradiation.The area is offset to the surface,and the near surface area forms severe radiation damage,possibly with the presence of small bubbles.X-ray diffraction results showed that the phase structure after irradiation did not change,and the defects caused bythe defects had little effect on the bulk structure in the sample.100 keV H⁺irradiated ODS steels and RAFM steels,the irradiation doses were 1×1015,1×1016,1×1017,respectively.The vacancy-type defects generated by hydrogen ions in ODS steels have a low binding energy between H⁺and vacancies,and easily form a complex with vacancies.The type of irradiation defect with a high injection dose of 1×1017 cm^-2 changes,mainly due to relatively large vacancies or voids and a large number of vacancy complexes in the transition from the irradiation zone to the matrix zone.As the irradiation dose increases,a large number of grain boundaries appear on the surface,and a large amount of precipitates are present at the edges thereof.The average grain size tends to increase with increasing irradiation dose,and the vacancy type defect has little effect on the bulk structure of the sample.Slow positron beam Doppler results show that the positron annihilation mechanism of RAFM steel has changed.When the implantation dose is 1×1015 cm^-2,the size of the defect does not change.The defect size under the experimental conditions of 1×1016 cm^-2 and 1×1017 cm^-2 is also increased with the dose.The increase was observed,and the size change of the 1×1017 cm^-2 irradiated sample was the most significant.AFM image showed slight swelling on the surface and a large number of small bubbles were generated.