Anomalous two-step repair mechanism of Al–Cu alloy regulated by the surroundings during E-beam irradiation

Understanding the repair mechanisms of defects is essential for gaining insight into improving the quality and enhancing the performance of materials. While new structures and elemental segregation always exist around defects, the influence of the surroundings on the repair mechanism has rarely been investigated on the atomic scale. Here, by tracking the morphological and microstructural evolution of Al2Cu nanopores with and without Cu-rich phases in the vicinity under electron beam irradiation, our in-situ transmission electron microscopy (TEM) study revealed a surrounding-dependent repair behavior. In contrast to the Al2Cu nanopores without Cu-rich neighborhoods, which display an isotropically shrinking from all directions, the Al2Cu nanopores with Al4Cu9 nearby exhibit an anomalous two-step repair mechanism. First, new Al4Cu9 structures nucleated from the Cu-rich region and evolved to fill the nanopores. Second, Al4Cu9 reacted with Al atoms and gradually transformed into Al2Cu. High-resolution TEM (HRTEM) images and strain maps demonstrate that the repair is imperfect as the eventual repaired region contains both Al4Cu9 and Al2Cu. This is caused by the simultaneous sputtering and depositing effects of electron beams (E-Beam). Our findings provide critical insights into the modulatory function of surroundings on the nanopore repair mechanism.