Role of axial twin boundaries on deformation mechanisms in Cu nanopillars

Abstract

In recent years, twinned nanopillars have attracted tremendous attention for research due to their superior mechanical properties. However, most of the studies were focused on nanopillars with twin boundaries (TBs) perpendicular to loading direction. Nanopillars with TBs parallel to loading direction have received minimal interest. In this backdrop, the present study is aimed at understanding the role of axial TBs on strength and deformation behaviour of Cu nanopillars using atomistic simulations. Tensile and compression tests have been performed on <112> nanopillars with and without TBs. Twinned nanopillars with twin boundary spacing in the range 1.6-5 nm were considered. The results indicate that, under both tension and compression, yield strength increases with decreasing twin boundary spacing and is always higher than that of perfect nanopillars. Under compression, the deformation in <112> perfect as well as twinned nanopillars proceeds by the slip of extended dislocations. In twinned nanopillars, an extensive cross-slip by way of Friedel-Escaig and Fleischer mechanisms has been observed in compression. On the other hand, under tensile loading, the deformation in perfect nanopillars occurs by partial slip/twinning, while in twinned nanopillars, it proceeds by the slip of extended dislocations. This extended dislocation activity is facilitated by stair-rod formation and its dissociation on the twin boundary. Similar to compressive loading, the extended dislocations under tensile loading also exhibit cross-slip activity in twinned nanopillars. However, this cross-slip activity occurs only through Fleischer mechanism and no Friedel-Escaig mechanism of cross-slip has been observed under tensile loading.

Plasticity through De-Twinning in Twinned BCC Nanowires

“…The deformation behaviour of [110] BCC Fe nanowires with twin boundaries oriented parallel to the loading direction were considered in this study (Figure 1). The nanopillar is enclosed by [1][2][3][4][5][6][7][8][9][10][11] and [1-1-2] type side surfaces. The number of TBs is varied from one to three (Figure 1a-c).…”

“…In order to understand the deformation behaviour of twinned FCC nanowires/nanopillars, many experimental and atomistic simulation studies have been carried out in the literature [2,[6][7][8][9]. The results have shown that depending on the orientation of the TBs with respect to the loading direction, deformation mechanisms vary in nanowires and also many novel deformation mechanisms have been reported.…”

Role of twin boundary position on the yield strength of Cu nanopillars

“…It has also been found that the strengthening effect of TBs strongly depends on the TB spacing [9,10,14,15]. Generally, the yield strength of twinned nanopillars increases with decreasing twin boundary (TB) spacing [10,13,14] resembling the Hall-Petch type behaviour in polycrystalline materials. This strengthening effect in twinned nanopillars has been attributed to the additional repulsive force exerted by TBs on dislocation nucleation and glide [16,17,18].…”

“…The introduction of TBs has become a well-known means of strengthening method in nanopillars and nanocrystalline materials. As a result, many experimental and atomistic simulation studies have been performed on twinned nanopillars containing high density of TBs [9,10,11,12,13]. These studies have revealed that the introduction of TBs increases the strength along with ductility of twinned nanopillars as compared to their twin free counterparts.…”

“…It becomes even more important since the plasticity in nanopillars is surface controlled [2,3,4] and TBs exerts repulsive force on dislocation nucleation [16,17,18]. Due to limited studies on twinned nanopillars containing longitudinal TBs [13,19,20], the role of TB position has not attracted the attention of researchers, especially on yield strength.…”