Mechanical properties of bimetallic crystalline and nanostructured nanowires

Abstract

Nanowires are basic components of interconnects at the nanoscale level in electronic as well as in electromechanical devices. Presently, there is a fast growing interest in their synthesis as well as in their mechanical testing. Focused ion beams now allow machining pillars with diameters as small as a few tens of nanometres and nanoindenter systems allow measuring strains at the atomic scale and compressive stresses up to the 10 GPa range. Such pillars typically contain less than millions of atoms, which makes their modelling and the modelling of their mechanical properties at the atomic scale realistic. A few Molecular Dynamics studies are presently available, discussing deformation mechanisms in thin narrow crystalline nanowires, but the literature about nanoalloy wires and nanostructured wires, as they can be synthesized from clusters, is almost non-existent. In the latter, the dislocation activity may be inhibited, leading to specific mechanical properties. By means of large scale computations, we use Ni3A1 to discuss the mechanical properties of crystalline and nanostructured nanowires. We also compare wires to their bulk counterparts. Both isothermal and isoenergetic whereby mechanical work converts into heat in the system-deformation mechanisms are considered. The comparison between pair correlation functions, stress distributions, configuration analysis and strain stress relations capture most of the stress-induced evolution mechanisms of nanowires with different diameters and structures, including elastic properties, dislocation activity, grain rotation and boundary motion, local melting, superplasticity and fracture. A structural transition which may be martensitic is predicted for the first time at the nanoscale level, suggesting possible shape memory properties of nanoalloy nanowires.

Simulation of positron annihilation response to mechanical deformation of nanostructured Ni3Al

“…At strains larger than e zz = 0.3, defects were also found inside grains because of the onset of a structural transformation (L1 2 to tetragonal; see Ref. [9] for details), which caused a further increase in the total FV1. Beyond this structural transformation, at strains larger than e zz = 0.85, defects are mainly found inside grains and defects' positions remain stable upon further deformation.…”

“…The detailed description of the sample preparation procedure and deformation experiment can be found in Ref. [9].…”