An atomistic study on the strain rate and temperature dependences of the plastic deformation Cu–Au core–shell nanowires: On the role of dislocations

Abstract

Recently, Cu–Au core–shell nanowires have been extensively used as conductors, nanocatalysts, and aerospace instruments due to their excellent thermal and electrical conductivity. In experimental studies, various methods have been presented for producing, characterizing, and strengthening these structures. However, the mechanical behavior and plastic deformation mechanisms of these materials have not been investigated at the atomic scale. Consequently, in the present study, we carried out uniaxial tensile tests on Cu–Au nanowires at various tension rates and temperatures by means of the molecular dynamics approach. The Cu–Au interface was found to be the main site for nucleation of perfect dislocations, Shockley partials, and stacking faults due to the stress concentration and high potential energy arising from the atomic mismatch between shell and core layers. It was observed that an increase in the strain rate from 108 to 1,011 s−1 shortened the time required for the nucleation of dislocations, decreasing the dislocation density. This emphasizes that dislocation nucleation and slip mechanisms are time-dependent. Moreover, it was found that the interaction of Shockley partials can lead to the creation of lock dislocations, such as Hirth, Frank, and Stair-rod dislocations, imposing obstacles for the slip of other dislocations. However, as the tension temperature rose from 300 to 600 K, opposite-sign dislocations removed each other due to thermally activated mechanisms such as dislocation climb and dislocation recovery. Furthermore, the combination of Shockley partial dislocations decreased the stacking fault density, facilitating the plastic deformation of these structures. The yield strength and elastic modulus of the samples increased with the strain rate and substantially decreased as the temperature rose.

Keywords

• cu–au core–shell
• plastic deformation
• strain rate
• temperature
• molecular dynamics approach