Superplastic Creep of Metal Nanowires from Rate-Dependent Plasticity Transition

WW Tao and PH Cao and HS Park, ACS NANO, 12, 4984-4992 (2018).

DOI: 10.1021/acsnano.8b02199

Understanding the time-dependent mechanical behavior of nanomaterials such as nanowires is essential to predict their reliability in nanomechanical devices. This understanding is typically obtained using creep tests, which are the most fundamental loading mechanism by which the time-dependent deformation of materials is characterized. However, due to existing challenges facing both experimentalists and theorists, the time-dependent mechanical response of nanowires is not well- understood. Here, we use atomistic simulations that can access experimental time scales to examine the creep of single-crystal face- centered cubic metal (Cu, Ag, Pt) nanowires. We report that both Cu and Ag nanowires show significantly increased ductility and superplasticity under low creep stresses, where the superplasticity is driven by a rate- dependent transition in defect nucleation from twinning to trailing partial dislocations at the micro- or millisecond time scale. The transition in the deformation mechanism also governs a corresponding transition in the stress-dependent creep time at the microsecond (Ag) and millisecond (Cu) time scales. Overall, this work demonstrates the necessity of accessing time scales that far exceed those seen in conventional atomistic modeling for accurate insights into the time- dependent mechanical behavior and properties of nanomaterials.

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