Abstract
The microstructural response of beryllium after neutron irradiation at various temperatures (643–923 K) was systematically studied using analytical transmission electron microscope that together with outcomes from advanced atomistic modelling provides new insights in the mechanisms of microstructural changes in this material. The most prominent feature of microstructural modification is the formation of gas bubbles, which is revealed at all studied irradiation temperatures. Except for the lowest irradiation temperature, gas bubbles have the shape of thin hexagonal prisms with average height and diameter increasing with temperature. A high number density of small bubbles is observed within grains, while significantly larger bubbles are formed along high-angle grain boundaries (GB). Denuded zones (DZ) nearly free from bubbles are found along both high- and low-angle grain boundaries. Precipitations of secondary phases (mainly intermetallic Al-Fe-Be) were observed inside grains, along dislocation lines and at GBs. EDX analysis has revealed homogeneous segregation of chromium and iron along GBs. The observed features are discussed with respect to the available atomistic modelling results. In particular, we present a plausible reasoning for the abundant formation of gas bubbles on intermetallic precipitates, observation of various thickness of zones denuded in gas bubbles and precipitates, and their relation to the atomic scale diffusion mechanisms of solute-vacancy clusters.
Highlights
The microstructural response of beryllium after neutron irradiation at various temperatures (643– 923 K) was systematically studied using analytical transmission electron microscope that together with outcomes from advanced atomistic modelling provides new insights in the mechanisms of microstructural changes in this material
Long-term irradiation tests in material research reactors provide important information about irradiation resistance of beryllium pebbles under close-to-fusion conditions regarding operation temperature, accumulated damage dose, amount of helium and tritium generated by neutron-induced transmutation, the energy spectrum of fusion neutrons cannot be exactly simulated by common nuclear reactors
Microstructural changes induced by neutron irradiation in beryllium were studied, both experimentally and by application of the first principles methods
Summary
The microstructural response of beryllium after neutron irradiation at various temperatures (643– 923 K) was systematically studied using analytical transmission electron microscope that together with outcomes from advanced atomistic modelling provides new insights in the mechanisms of microstructural changes in this material. Investigations of beryllium microstructure after irradiation allow qualification of material properties for its prospective nuclear fusion reactor applications[3], and contribute significantly to the physical understanding of the underlying mechanisms of microstructural changes in hexagonal closed packed metals under irradiation or high temperature aging in general Such investigations provide by analogy better understanding of the microscopic processes occurring in materials with other lattice structures. This paper presents systematic analytical transmission electron microscopy (TEM) studies of the microstructural changes in neutron irradiated beryllium pebbles reaching a damage dose and gas production of 37 dpa, 5900 appm 4He and 640 appm 3H, respectively These experimental results are discussed based on ab initio simulations of solute-vacancy interactions, migration energies for solute atom diffusion and their implications for solute migration mechanisms and anisotropy of denuded zones
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