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.