Effect of Aspect Ratio on the Deformation Behavior of Dislocation-Free Ni₃Al Nanocubes

This study concentrates on several factors which govern the nanoscale plasticity of in situ compressed dislocation-free Ni₃Al nanocubes: cube size, aspect ratio and the presence of grooves. The yield strength of dislocation-free Ni₃Al nanocubes exhibits an apparent size dependence. The size dependence is strong when cubes are smaller than 300 nm. Compared with the strength of bulk Ni₃Al 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.