Characterization of the strain rate dependent behavior of nanocrystalline gold films

The strain rate dependence of freestanding, nanocrystalline gold films was evaluated by a microtensile technique with applied strain rates on the order of 10⁻⁴ to 10⁻⁶ s⁻¹. Film thickness ranged from 0.25 to 1.00 μm with corresponding grain sizes of 40 to 100 nm. The plastic properties were found to be particularly sensitive to strain rate, film thickness, and grain size, while the elastic property remained relatively unchanged. The thinner films exhibited significant strain rate sensitivity, while the thicker film exhibited only marginal changes. Hall–Petch boundary hardening was observed and dominated plastic flow at larger strain rates, while diffusion-controlled deformation mechanisms appeared to be activated with increasing influence as strain rate decreased. Analysis of dislocation-based and grain-boundary diffusion-related creep suggested that the films were likely experiencing power-law creep as the dominant deformation mechanism in this grain size regime at lower strain rates.