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Molecular dynamics simulations performed on 110 Cu nanopillars revealed significant difference in the deformation behavior of nanopillars with and without twin boundary. The plastic deformation in single crystal Cu nanopillar without twin boundary was dominated by twinning, whereas the introduction of twin boundary changed the deformation mode from twinning to slip consisting of leading partial followed by trailing partial dislocations. This difference in deformation behavior has been attributed to the formation of stair-rod dislocation and its dissociation in the twinned nanopillars.

Molecular dynamics simulations were performed to understand the role of twin boundaries on deformation behaviour of body-centred cubic (BCC) iron (Fe) nanopillars. The twin boundaries varying from one to five providing twin boundary spacing in the range 8.5 -2.8 nm were introduced perpendicular to the loading direction. The simulation results indicated that the twin boundaries in BCC Fe play a contrasting role during deformation under tensile and compressive loadings. During tensile deformation, a large reduction in yield stress was observed in twinned nanopillars compared to perfect nanopillar. However, the yield stress exhibited only marginal variation with respect to twin boundary spacing. On the contrary, a decrease in yield stress with increase in twin boundary spacing was obtained during compressive deformation. This contrasting behaviour originates from difference in operating mechanisms during yielding and subsequent plastic deformation. It has been observed that the deformation under tensile loading was dominated mainly by twin growth mechanism, due to which the twin boundaries offers a negligible resistance to slip of twinning partials. This is reflected in the negligible variation of yield stress as a function of twin boundary spacing. On the other hand, the deformation was dominated by nucleation and slip of full dislocations under compressive loading. The twin boundaries offer a strong repulsive force on full dislocations resulting in the yield stress dependence on twin boundary spacing. Further, it has been observed that the curved twin boundary can acts as a source for full dislocation. The occurrence of twin-twin interaction during tensile deformation and dislocation-twin interaction during compressive deformation were presented and discussed.In recent years, the twinned nanopillars or nanowires have drawn growing attention in view of their superior physical properties and potential applications in modern small-scale electronic devices such as nano/micro electro mechanical systems. The twinned nanopillars contain a series of twin boundaries with specified spacing between the boundaries. Twin boundary possesses high symmetry and lowest interface energy along with well-defined boundary plane. The low energy of twin boundaries results in a number of superior properties over conventional grain boundaries. For example, it has been found that the twin boundaries enhance the strength without loss of ductility [1-3], improve fracture toughness and crack resistance [4][5][6], and increase corrosion resistance and strain rate sensitivity [7]. Moreover, the twin boundaries possess high thermal and mechanical stability [8,9] and high electrical conductivity [10]. The superior mechanical properties of twinned nanopillars have been attributed to unique deformation mechanisms operating in the presence of twin boundaries [11]. In view of this, the materials containing high density of twin boundaries attract huge interest among materials scientists and engineers.Several experimental and molecular dynamics (MD) sim...