Mechanical behavior of reactive Al/Ni multilayers by molecular dynamics simulations

Due to the focus on their high reactivity, the mechanical properties of Al/Ni multilayer nanofoils have not yet been investigated extensively. However, as Al/Ni multilayers are potentially going to be integrated into various applications, it is also important to understand their mechanical properties. In this paper, molecular dynamics simulations are used to investigate the mechanical properties, namely hardness and Young's modulus, of Al/Ni multilayers via nanoindentation. Furthermore, the results are contextualized by comparison with simulated uniform uniaxial compression. The following essential features have been investigated: the influence of the grain orientation, of a naturally occurring premixed interlayer at the Al-Ni interface, and ultimately of the bilayer height on the mechanical properties is explored. An inverse Hall-Petch effect is observed, meaning that both hardness and Young's modulus decrease with decreasing bilayer height. At the same time, the modulus-to-hardness ratio increases with decreasing bilayer height. Premixed interlayers only show an effect on the mechanical properties for very small bilayer heights, where they make up a clear majority of volume fraction of the full system. The mechanical properties obtained from nanoindentation are in good agreement with those obtained from uniaxial compression. Insights from this study might be transferred to other fcc/fcc multilayer systems.