Materials Science and Engineering A 423 (2006) 97–101 Atomistic simulations of mechanical deformation of high-angle and low-angle nanocrystalline copper at room temperature C. Zheng, Y.W. Zhang ∗ Department of Materials Science and Engineering, National University of Singapore, Singapore 119260, Singapore Received 8 July 2005; received in revised form 11 January 2006; accepted 17 January 2006 Abstract Molecular dynamics simulations were performed to study the mechanical behavior of high-angle and low-angle nanocrystalline copper with the average grain size in the range of 3.7–6.7 nm at room temperature. Atomic configuration analysis indicates that the grain boundary sliding is the main deformation mechanism in the high-angle samples while both dislocation motion and grain boundary activities play an important role in the plastic deformation for low-angle (textured) samples. The grain boundary activities in the low-angle samples are manifested by migration, breakup and dislocation activities within grain boundaries themselves. It was found that the orientation of the grains to the tensile direction strongly affects the mechanical behavior of the textured samples. © 2006 Elsevier B.V. All rights reserved. Keywords: Nanocrystalline materials; Molecular dynamics; Plastic deformation; Copper 1. Introduction The deformation mechanisms of metals with the average grain size in the nanometer range are still controversial. Numer- ous experimental data support the normal Hall–Petch relation, that is, the yield stress of the metals increases with a decrease in grain size even when the average grain size is decreased down to the nanometer range [1,2]. The underlying mechanism for this argument is that dislocation-dominated mechanisms such as dislocation pile-ups at the grain boundaries prevail. How- ever, molecular dynamics simulations have indicated an inverse Hall–Petch relation, that is, the flow stress decreases with a decrease in grain size when the average grain size goes down to approximately 12 nm [3–7]. This inverse Hall–Petch relation is also supported by some experimental results [8,9]. The dominant mechanism for this argument is grain boundary sliding since dis- location sources within the small grains can hardly exist and the small grains cannot sustain dislocation pile-ups [3–7]. Grain boundaries play an important role in the mechanical behavior of nanocrystalline metals. The term ‘low-angle grain boundary’ is used if the misalignment is small, usually less than 17 ◦ [5]. Otherwise, the term ‘high-angle grain boundary’ is used. ∗ Corresponding author. Fax: +65 67763604. E-mail address: msezyw@nus.edu.sg (Y.W. Zhang). In contrast to high-angle grain boundaries, the obstacle of low- angle boundaries to dislocation motion is much less effective since dislocations can find a matching Burgers vector in the neighboring grains. Also the relatively ordered atomic struc- tures make low-angle grain boundaries more difficult to slide. Thus it is expected that different deformation behavior arises for nanocrystalline metals with these two types of grain boundaries. Previous atomistic simulations mainly focus on nanocrystalline metals with high-angle grain boundaries [3,4,6,7]. Here, we compare the different deformation behavior in high-angle and low-angle nanocrystalline copper with an average grain size in the range of 3.7–6.7 nm and examine their deformation mecha- nisms. In addition, we investigate the effects of the orientation of the texture in the low-angle grain boundary samples on the plastic behavior of nanocrystalline copper. 2. Methodology We create our samples in a cubic simulation cell with a side length of 12 nm, filling it with 65, 30 and 11 randomly located seeds, and resulting in the average grain size ranging from 3.7 to 6.7 nm. Each sample contains approximately 140,000 atoms. The microstructure of the nanocrystalline samples is produced by the Voronoi construction [10]. Each cell is filled with atoms in an fcc lattice with a randomly crystallographic orientation. Then 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.01.040