The behaviour of inert gas produced in irradiated alloys.

Hastings, Ian James. (1968). The behaviour of inert gas produced in irradiated alloys. PhD Thesis, , The University of Queensland.

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Author Hastings, Ian James.
Thesis Title The behaviour of inert gas produced in irradiated alloys.
Institution The University of Queensland
Publication date 1968
Thesis type PhD Thesis
Total pages 138
Language eng
Subjects 091207 Metals and Alloy Materials
860601 Industrial Gases
Formatted abstract
The present work utilises X-Ray Diffraction, Internal Friction, Density and Electron Microscopy techniques to define the behaviour of inert gases produced in irradiated material. Investigations were carried out in the temperature range 20°C - 900°C upon neutron irradiated copper-boron alloys containing helium.

Prior to precipitation the helium atoms occupy interstitial sites in the copper lattice. A hardening effect determined by internal friction and dependent upon irradiation dose and helium concentration is described for irradiated samples. As an intermediate step towards bubble formation, the helium atoms associate with between 1 and 4 vacancies and enter substitutional solution. The activation energy of 0.76 ± 0.1 eV obtained for this process is of the same magnitude as that for vacancy migration. However, the rate controlling mechanism was not positively identified. The atom-vacancy complexes combine to form bubble nuclei, and growth occurs by vacancy migration to embryo bubbles. An activation energy of 0.95 ± 0.1 eV was measured for the migration of helium atom-vacancy complexes during this stage. A qualitative model, taking into account the processes of interstitial-substitutional movement of helium atoms, and gas precipitation, is proposed. The rate of gas precipitation is strongly dependent upon temperature and inert gas concentration. Gas precipitation occurs during irradiation at - 80°C for a minimum gas concentration which lies between 0.04 and 0.06 at.% He4 .

Dislocations produced by the annealing of irradiation damage are preferential sites for bubble nucleation, however there is also some evidence for limited homogeneous nucleation. The growth of bubbles occurs by a migration and coalescence mechanism, with the average bubble radius proportional to t ^' in the initial stages, where t is the annealing time. However, a relatively stable bubble size and distribution is quickly established on the dislocation network, and subsequent growth is only weakly dependent upon annealing time. Initially the bubbles are spherical, but subsequently they develop crystallographic shapes with major faces parallel to both cube {100} and octahedral {111} planes. Elongated bubbles with similar preferred faces are observed after high temperature irradiation.

Grain boundary parting, accompanied by gross swelling occurs at temperatures above 700°C, with the process strongly dependent upon temperature and gas concentration. Grain boundary bubbles grow spontaneously by vacancy absorption until, they touch. An activation energy of 1.95 ± 0.2 eV has been obtained for the degeneration mechanism. This is close to that for volume diffusion of vacancies in copper.

An effect involving concentric damaged areas surrounding boron particles in irradiated Cu-B10 alloys is reported. The damage is produced by He4 and Li7 resulting from the transmutation of B10
Keyword Gases, Rare.

Document type: Thesis
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