Deformation mechanism of kink-step distorted coherent twin boundaries in copper nanowire

Bobin Xing; Shaohua Yan; Wugui Jiang; Qing H. Qin; Bobin Xing; Shaohua Yan; Wugui Jiang; Qing H. Qin

doi:10.3934/matersci.2017.1.102

AIMS Materials Science

2017, Volume 4, Issue 1: 102-117. doi: 10.3934/matersci.2017.1.102

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Deformation mechanism of kink-step distorted coherent twin boundaries in copper nanowire

1.
Research School of Engineering, Australian National University, Acton, ACT 2601, Australia
2.
School of Aeronautical Manufacturing Engineering, Nanchang Hangkong University, Nanchang 330063, China

Received: 08 November 2016 Accepted: 27 December 2016 Published: 05 January 2017

In the construction of nanotwinned (NT) copper, inherent kink-like steps are formed on growth twin boundaries (TBs). Such imperfections in TBs play a crucial role in the yielding mechanism and plastic deformation of NT copper. Here, we used the molecular dynamic (MD) method to examine the influence of kink-step characteristics in depth, including kink density and kink-step height, on mechanical behavior of copper nanowire (NW) in uniaxial tension. The results showed that the kink-step, a stress-concentrated region, is preferential in nucleating and emitting stress-induced partial dislocations. Mixed dislocation of hard mode I and II and hard mode II dislocation were nucleated from kink-step and surface atoms, respectively. Kink-step height and kink density substantially affected the yielding mechanism and plastic behavior, with the yielding stress functional-related to kink-step height. However, intense kink density (1 kink per 4.4 nm) encourages dislocation nucleation at kink-steps without any significant decline in tensile stress. Defective nanowires with low kink-step height or high kink density offered minimal resistance to kink migration, which has been identified as one of the primary mechanisms of plastic deformation. Defective NWs with refined TB spacing were also studied. A strain-hardening effect due to the refined TB spacing and dislocation pinning was observed for defective NWs. This study has implications for designing NT copper to obtain optimum mechanical performance.
- molecular dynamic simulation,
- nanotwins,
- dislocations,
- defective twins
Citation: Bobin Xing, Shaohua Yan, Wugui Jiang, Qing H. Qin. Deformation mechanism of kink-step distorted coherent twin boundaries in copper nanowire[J]. AIMS Materials Science, 2017, 4(1): 102-117. doi: 10.3934/matersci.2017.1.102

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Abstract

In the construction of nanotwinned (NT) copper, inherent kink-like steps are formed on growth twin boundaries (TBs). Such imperfections in TBs play a crucial role in the yielding mechanism and plastic deformation of NT copper. Here, we used the molecular dynamic (MD) method to examine the influence of kink-step characteristics in depth, including kink density and kink-step height, on mechanical behavior of copper nanowire (NW) in uniaxial tension. The results showed that the kink-step, a stress-concentrated region, is preferential in nucleating and emitting stress-induced partial dislocations. Mixed dislocation of hard mode I and II and hard mode II dislocation were nucleated from kink-step and surface atoms, respectively. Kink-step height and kink density substantially affected the yielding mechanism and plastic behavior, with the yielding stress functional-related to kink-step height. However, intense kink density (1 kink per 4.4 nm) encourages dislocation nucleation at kink-steps without any significant decline in tensile stress. Defective nanowires with low kink-step height or high kink density offered minimal resistance to kink migration, which has been identified as one of the primary mechanisms of plastic deformation. Defective NWs with refined TB spacing were also studied. A strain-hardening effect due to the refined TB spacing and dislocation pinning was observed for defective NWs. This study has implications for designing NT copper to obtain optimum mechanical performance.

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