National Research Nuclear University MEPhI, Moscow, Russia:

M. S. Staltsov, Associate Professor at the Department of Physical Problems of Materials Science, Candidate of Physical and Mathematical Sciences
I. I. Chernov, Professor at the Department of Nuclear Physics and Technology at the Office for Educational Programmes1, Doctor of Physical and Mathematical Sciences, Professor, e-mail: i_chernov@mail.ru

This paper is the second part of a three-part review that looks at the effect of doping elements on the behaviour of helium and hydrogen, the development of gas porosity, as well as the amount of hydrogen retained in alloys of vanadium with Ti, Cr, W and Ta. The paper describes the results of a study that looked at the microstructure of low-activation binary and ternary alloys of vanadium irradiated with helium ions at 650 ^оС. It is shown that when tungsten is used as the doping element, it results in much bigger bubbles that form, enhancing the gas swelling of the alloys. When tantalum is introduced in the binary alloy V – 2 % W, it restrains the swelling and bubbles of minimum size get formed in the V – Zr and V – Ti alloys, and they are prone to minimal swelling. A study that looked at hydrogen retention in vanadium alloys that are successively irradiated with helium and hydrogen ions helped establish that a prior Не⁺ irradiation at 20 ^оС leads to a larger amount of hydrogen retained during the following ion-beam implantation of hydrogen, while the helium porosity created as the result of high-temperature Не⁺ irradiation leads to an even larger amount of retained hydrogen. A thermodesorption spectroscopy study demonstrates that when the following irradiation sequence is used: He⁺ (Т_irrad = 650 ^оС) + H⁺ (Т_irrad = 20 ^оС), the V – 4% W retains 1.4 times and V – 1 % Zr – 2.2 times more hydrogen than vanadium does. Unlike it is with vanadium alloys with Ti, Cr and W, in the case of V – Ta alloys the authors found a great amount of bubbles formed at the depths of up to 900 nm, which significantly exceed the theoretical path of 40 keV (~300 nm) Не+ ions. When irradiation was carried out with 40 keV Не⁺ ions to the fluence of 5.1020 m^–2 at 650 ^оС and then successively with 7.5 MeV Ni²⁺ to the dose of 100 DPA at 650 ^оС at the depths that significantly exceeded the Не⁺ ion path, the authors found helium bubbles (or gas-filled pores), which were not present when irradiation was carried out with Ni²⁺ ions only.

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