Abstract
The atomic-scale defects such as (deuterium, helium)-vacancy clusters in nuclear energy materials are one of the causes for the deterioration of the macroscopic properties of materials. Unfortunately, they cannot be observed by transmission electron microscopy (TEM) before they grow to the nanometer scale. Positron annihilation spectroscopy (PAS) has been proven to be sensitive to open-volume defects, and could characterize the evolution of the size and concentration of the vacancy-like nanoclusters. We have investigated the effects of He-D interaction on the formation of nanoscale cavities in Fe9Cr alloys by PAS and TEM. The results show that small-sized bubbles are formed in the specimen irradiated with 5 × 1016 He+/cm2, and the subsequent implanted D-ions contribute to the growth of these helium bubbles. The most likely reason is that helium bubbles previously formed in the sample captured deuterium injected later, causing bubbles to grow. In the lower dose He-irradiated samples, a large number of small dislocations and vacancies are generated and form helium-vacancy clusters with the helium atoms.
Highlights
The size of the dislocation loop formed in helium/deuterium sequential-ion irradiated sample was larger than that of helium single-ion irradiated specimen, which indicates that the subsequent
No bubbles were observed in the sample irradiated by helium/deuterium sequential ion, which may be that the irradiation doses were lower and the irradiations were performed at room temperature
The effects of He-D interaction on the formation of nanoscale cavities in Fe9Cr alloys have been studied by Positron annihilation spectroscopy (PAS) and transmission electron microscopy (TEM)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. F82H [1], JLF-1 [2], EUROFER97 [3], 9Cr-2WVTa [4], and CLAM [5] Such steels are candidate structural materials for future nuclear reactors and possibly for long-term spallation neutron sources used for transmutation of spallation products. They have the advantages of low activation, excellent void-swelling resistance, and suppressed hydrogen/helium embrittlement. Reported works indicate that hydrogen isotope and helium atoms could interact with irradiation-induced vacancy defects, and they could migrate and aggregate to form (H/He)-vacancy clusters or bubbles, which might cause undesired changes in the material properties [9,10]. We would like to generalize the characterization method of positron annihilation spectroscopy, which is useful in metal materials, and useful in the study of micro-nano scale defects in 2D materials and semiconductor devices
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