Effect of Aspect Ratio on the Deformation Behavior of Dislocation-Free NiAl Nanocubes.

This study concentrates on several factors which govern the nanoscale plasticity of in situ compressed dislocation-free NiAl nanocubes: cube size, aspect ratio and the presence of grooves. The yield strength of dislocation-free NiAl nanocubes exhibits an apparent size dependence. The size dependence is strong when cubes are smaller than 300 nm. Compared with the strength of bulk NiAl single crystals, the strength of nanocubes is two orders of magnitude higher, which clearly demonstrates that there is a size effect. Nanocube plasticity strongly depends on the alignment and the shape of the cubes. Deformed aligned nanocubes either display only a few localized deformation events (slip lines) or were homogenously compressed into flats due to multiple slip dislocation-mediated plasticity. For an aligned cube, crack initiation at the intersection of a slip line with a groove in the cube surface was observed. In case of a double cube, crack initiation occurs at surface irregularities, while subsequent crack propagation occurs along one or more slip planes.