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We examine the processes of spherical indentation and tension in Ni nanowires and thin films containing random distributions of nanoscale grains by molecular dynamics simulations. It is shown that the resistance to nanoindentation of nanocrystalline Ni nanowires with diameters of 12 and 30 nm tends not to depend on the wire diameter and free surfaces, contrary to nanoindentation in single-crystalline nanowires. Accommodation of plastic deformation by grain boundary sliding suggests a mitigation strategy for sample boundary effects in nanoscale plasticity.

The effects of twin size and sample diameter on yield stress and surface dislocation emission in twinned metal nanowires deformed uniformly were studied using classical dislocation theory and the concept of image force from twin boundaries. This theoretical study is shown to quantitatively capture the linear increase in yield stress as twin size decreases in periodically twinned Au nanowires predicted by atomistic simulations. The implication of this model as a yield criterion for realistic metal nanostructures with nanoscale growth twins is discussed.

Nanocrystalline (50-μm-thick) Ni films with controlled surface morphology at the nanoscale were synthesized by direct-current electrodeposition of Ni on an Si substrate under different electrochemical conditions. A relationship between spatial roughness scaling and mean grain size in electrodeposited Ni was established using X-ray diffraction and atomic force microscopy. Fractal analysis showed a transition from self-affine to ultrasmooth surfaces. A non-destructive method is demonstrated to estimate the grain size distribution of ultrasmooth nanocrystalline Ni surfaces by atomic force microscopy with high-resolution probes.