Mechanically Driven Grain Boundary Formation in Nickel Nanowires

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Metallic nanomaterials are crucial for micro/nanodevices.
• Understanding mechanical deformation, especially under stress/strain gradients, is vital but unclear.
• The evolution of microstructure during plastic deformation in nanomaterials requires further investigation.

Purpose of the Study:

• To investigate the in situ microstructure evolution of nickel (Ni) nanowires during bending.
• To elucidate the role of strain gradients and dislocations in grain boundary (GB) formation.
• To understand the transformation of low-angle GBs to high-angle GBs under mechanical stress.

Main Methods:

• In situ bending experiments on Ni nanowires with nanoscale twin lamellae.
• High-resolution transmission electron microscopy (HRTEM) for atomic-scale imaging.
• Atomistic simulations to analyze strain gradients and geometrically necessary dislocations.

Main Results:

• Localized bending deformation induced the formation of a low-angle tilt grain boundary (GB) with dislocations.
• Intensified plastic deformation led to severe lattice distortion and collapse within the GB region.
• The low-angle GB transformed into a high-angle GB due to the accumulation of deformation.

Conclusions:

• Bending-induced strain gradients and geometrically necessary dislocations are key to GB formation in Ni nanowires.
• The study provides a detailed understanding of mechanically driven microstructure changes via GB evolution.
• Findings have implications for refining grain structures in bulk nanocrystalline materials.