Absorption of Nitrogen at Al/Al2O3 Interfaces in Al Nanocomposites: A Computational Analysis

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  • This research was sponsored by the U.S. Army Research Laboratory (ARL) and was accomplished under Cooperative Agreement W911NF-08-2-0028. The views, opinions, and conclusions made in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of ARL or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. The authors are grateful to Dr. Wei Liu at the Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin-Dahlem, Germany for technical discussions and insights. Supporting Information is available from the Wiley Online Library or from the author.

Abstract

The presence of nitrogen in nanostructured aluminum composites milled in liquid nitrogen has been argued to be responsible for reported property improvements, such as high strength and thermal stability. However, it has been experimentally difficult to precisely determine the nature of the nitride phases that form given their small scale (e.g., nm) and limited volume fraction. Moreover, the mechanism by which the nitrogen molecules are absorbed into the aluminum lattice during the cryomilling process remains poorly understood, and experimental studies are often constrained by resolution limits. In this paper, the absorption of nitrogen in Al-alloy composites during cryomilling is investigated from a computational perspective with the aid of the molecular dynamics simulation function in Materials Studio® software. Results indicate that Mg solute atoms in the matrix tend to segregate to Al/Al2O3 interfaces, creating vacancies in the Al lattice and subsequently enhancing the absorption of nitrogen into the Al lattice. The simulations also reveal that not only free N atoms but also N2 molecules can be absorbed into the Al lattice by occupying an Al vacancy. In addition, it is demonstrated that a structural defect, i.e., the presence of vacancies regardless of their source, is a requirement for enhanced absorption of nitrogen in the Al lattice.

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