Role of columnar structure on the fracture anisotropy of physical vapor deposited Al/SiC nanolaminates

Abstract In this work, the effect of layer thickness on the mechanical anisotropy of physical vapor deposited Al/SiC nanolaminate was explored by micropillar compressions at directions perpendicular (90°) and parallel (0°) to layer orientations. The role of inherent columnar structure on the fracture mechanism at both loading directions was highlighted. The results evidenced that the Al/SiC micropillar compressed at 90° was strengthened significantly as the layer thickness reduced, due to the constraint of Al plasticity (imposed by stiff SiC layers) and ruptures of SiC layers, both were layer thickness dependent. The constraint was weakened by the ruptures of SiC layers and the inherent columnar structures. Finite element modeling evidenced that the latter may trigger early formations of shear bands crossing multiple layers, leading to decreased strain hardening rate and ultimate compressive strength of the Al/SiC micropillar. The strengthening effect was reversed at 0°, with lower strength obtained in thinner layered micropillars. Finite element modeling of micropillar compression suggested that this is mainly a consequence of the inherent columnar structure that weakened remarkably the compressive strength, due to the kinking/buckling of the ceramic layers. This was further evidenced by the detailed transmission electron microscopy observations.