Mechanical behavior of aluminum–silicon nanocomposites: A molecular dynamics study

The mechanisms of deformation and failure in Al–Si nanocomposites, formed by adding Si particles to Al nanocrystalline materials, are investigated using molecular dynamics. The deformation and fracture mechanisms are found to be different in the Al–Si composites as compared to single-phase all-Al materials. The plastic deformation of all-Al polycrystals is associated with a mix of grain boundary deformation and dislocation activity while the deformation in the Al–Si nanocomposites is associated with predominantly grain boundary sliding/shearing at the Al/Si interfaces and little deformation elsewhere. The Al–Si nanocomposites also have a higher yield stress than the all-Al nanocrystals, consistent with recent experimental data. The failure of the Al polycrystals occurs by crack initiation at triple junctions and grain boundaries accompanied by localized shearing, leading to either trans- or intergranular cracks, while failure in the Al–Si nanocomposites occurs by void damage accumulation, culminating in crack formation, at an Al/Si interface. The tensile strength in the Al–Si nanocomposites correlates well with the fundamental Al/Si interface strength when the interface stress concentration caused by the modulus mismatch is considered. In spite of very different failure modes, the tensile strengths of the Al–Si and all-Al materials are similar. These results show that Al/Si interfaces control the mechanical behavior in the nanocomposites, reducing the role of bulk metal deformation modes, indicating that Al–Si nanocomposites can be engineered for enhanced hardness over all-Al nanocrystals of the same grain size.