In-situ study of one-dimensional motion of interstitial-type dislocation loops in hydrogen-ion-implanted aluminum

Abstract

The one-dimensional (1D) glide motion of dislocation loops along the direction of Burgers vector in various metallic materials has attracted considerable attention in recent years. During the operation of nuclear fusion reactor, component materials will be bombarded by high energy neutrons, resulting in production of radiation defects such as self-interstitial-atoms (SIAs), vacancies and their clusters. These defects feature large difference in migration energy, which may lead to concentration imbalance between SIAs and vacancies, and eventually irradiation damages such as swelling and embrittlement. Generally speaking, the mobility of a defect cluster is lower than that of a point defect. However, fast 1D motion may also take place among SIA clusters in the form of prismatic dislocation loops. This increases the transport efficiency of SIAs towards grain boundaries, surface and interface sites in the material, in favour of defect concentration imbalance and damage accumulation. To date, most literature works have found that the 1D motion of dislocation loops exhibited short-range (nanometer-scale) character. In addition, such experimental studies were generally conducted in pure metals using high voltage electron microscopes (HVEM) operated at acceleration voltages ≥1000 kV. However, for pure aluminum (Al), the maximum transferable kinetic energy from 200 keV electrons is 19.5 eV, while the displacement threshold energy is only 16 eV. Therefore, the observation and mechanistic investigation of 1D motion of dislocation loops in Al should also be possible with conventional transmission electron microscopes (C-TEM), as it may also exhibit the effects of beam heating and point defect production in HVEM. In view of the shortage of HVEM, this work reports the 1D motion of dislocation loops in pure Al implanted with hydrogen ions using C-TEM. Simultaneous dislocation loop motion in opposite directions of Burgers vector 1/2<inline-formula><tex-math id="Z-20211226170459">\begin{document}$\left\langle {110} \right\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170459.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170459.png"/></alternatives></inline-formula>has been captured, as well as the collective 1D motion of an array of dislocation loops in the direction of Burgers vector 1/3<inline-formula><tex-math id="Z-20211226170340">\begin{document}$\left\langle {111} \right\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170340.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170340.png"/></alternatives></inline-formula> under 200 keV electron irradiation. In addition, 1D motion of dislocation loops up to micron-scale range along the direction of Burgers vector 1/3<inline-formula><tex-math id="Z-20211226170427">\begin{document}$\left\langle {111} \right\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170427.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170427.png"/></alternatives></inline-formula>, and up to a few hundred nanometers range along the direction of Burgers vector 1/2<inline-formula><tex-math id="Z-20211226170442">\begin{document}$\left\langle {110} \right\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170442.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211229_Z-20211226170442.png"/></alternatives></inline-formula> have been found, which is different from previous literature works. A characteristic migration track would form behind the moving dislocation loop, lasting for about tens of seconds. The more rapid the dislocation loop motion, the longer the migration track length is. The concentration gradient of SIAs by electron irradiation and the redistribution of hydrogen atoms caused by the moving dislocation loops may account for the observed micron-scale 1D motion of dislocation loops and the migration tracks.