Molecular dynamics simulation of a solid platinum nanowire under uniaxial tensile strain: Temperature and strain-rate effects

Nanoscale research has been an area of active research over the past fifteen years. This is due to the overall enhanced properties of nanomaterials due to size effects, surface effects, and interface effects, which typically showed up in materials with characteristic size smaller than 100 nm. This study focuses on the molecular dynamics (MD) simulation of an infinitely long, cylindrical platinum nanowire, with an approximate diameter of 1.4 nm. The nanowire was subjected to uniaxial tensile strain along the [001] axis. The changes in crystal structure during deformation were analyzed and its mechanical properties were deduced from the simulation. Classical MD simulation was employed in this study, with the empirical Sutton-Chen pair functional used to describe the interatomic potential between the platinum atoms. The Berendsen loose-coupling thermostat was selected for finite-temperature control of the simulated system, with a time constant of 25% of the total relaxation time during each strain increment. The nanowire was subjected to strain rates of 0.04%, 0.4%, and 4.0% ps-1, at simulation temperatures of 50 and 300 K, in order to study the effects of different strain rates and thermal conditions on the deformation characteristics and mechanical properties of the nanowire. It was found that the stress-strain response of the nanowire showed clear periodic, stepwise dislocation-relaxation-recrystallization behavior at low temperature and strain rate, where crystal order and stability were highly preserved. The onset of amorphous crystal deformation occurred at 0.4% ps-1, and fully amorphous deformation took place at 4.0% ps-1, with amorphous melting detected at 300 K. Due to higher entropy of the nanowire at higher temperature and strain rate, periodic stress-strain behavior became less clearly defined, and superplasticity behavior was observed. This characteristic was significantly enhanced due to the development of a single-walled helical substructure at 300 K, when the nanowire was deformed at a lower strain rate. The Young's modulus was found to be about 50% to 75% that of its bulk counterpart, while the Poisson ratio was not significantly changed at the nanoscale.