Suppressed Size Effect in Nanopillars with Hierarchical Microstructures Enabled by Nanoscale Additive Manufacturing

Area of Science:

• Materials Science
• Mechanical Engineering
• Nanotechnology

Background:

• Mechanical size effects in nanosized metals are crucial for understanding properties.
• Previous studies focused on uniform microstructures and their strength as a function of diameter.
• Hierarchical microstructures and their influence on mechanical behavior require further investigation.

Purpose of the Study:

• To develop an additive manufacturing (AM) technique for producing metals with controlled hierarchical microstructures.
• To investigate the mechanical properties, specifically yield strength and deformation modes, of AM-fabricated nickel nanopillars.
• To explore the relationship between hierarchical microstructures, size effects, and mechanical response in nanosized metals.

Main Methods:

• Utilized a hydrogel infusion-based additive manufacturing technique with two-photon lithography to create Ni nanopillars (D ~ 130-330 nm).
• Characterized the hierarchical microstructures, revealing nanoporosity and nanocrystalline grains (d ~ 30-50 nm) in bamboo-like arrangements.
• Performed in situ nanocompression experiments and molecular dynamics simulations to analyze mechanical behavior and deformation modes.

Main Results:

• AM-fabricated Ni nanopillars exhibited hierarchical structures with nanopores and nanocrystalline grains.
• Yield strengths (σ) ranged from 1-3 GPa, exceeding those of uniform counterparts, with a weak size dependence (σ ∝ D^-0.2).
• Nanoporosity mediated a transition in deformation modes from localized to homogenized, as confirmed by simulations.

Conclusions:

• Hierarchical microstructures significantly influence the mechanical response of nanosized metals.
• The developed AM technique enables the engineering of complex microstructures for tailored mechanical properties.
• This research opens avenues for small-scale engineering applications leveraging AM-enabled hierarchical designs.