Abstract
Deformation twinning, one of the major deformation modes in a crystalline material, has typically been analyzed using generalized planar fault energy (GPFE) curves. Despite the significance of these curves in understanding the twin nucleation and its effect on the mechanical properties of crystals, their experimental validity is lacking. In this comparative study based on the first-principles calculation, molecular dynamics simulation, and quantitative in-situ tensile testing of Al nanowires inside a transmission electron microscopy system, we present both a theoretical and an experimental approach that enable the measurement of a part of the twin formation energy of the perfect Al crystal. The proposed experimental method is also regarded as an indirect but quantitative means for validating the GPFE theory.
Highlights
A twin is a planar defect, which is formed when partial slip occurs under the action of shear stress on more than three consecutive layers of the {111} plane
The mechanism for the formation of deformation twinning (DT) has typically been explained by the generalized planar fault energy (GPFE) curve, which depicts the energy landscape corresponding to twin nucleation and subsequent migration of the neighboring planes (Christian and Vítek 1970; Tadmor and Hai 2003; Vitek 1968)
We performed comparative studies to evaluate the twin formation energy using the atomic-scale simulations and the state-of-the-art in-situ transmission electron microscopy (TEM) tensile test of Al NWs. This was achieved by first deriving an equation that enables the estimation of the twin formation energy from the GPFE curve obtained for a perfect Al crystal using the first-principles calculations
Summary
A twin is a planar defect, which is formed when partial slip occurs under the action of shear stress on more than three consecutive layers of the {111} plane. Among various metal NWs, Al NWs due to their high SFE (~ 150 mJ m− 2) are known to deform via dislocation slip, but not via DT (Nabarro and Duesbery 2002) They can be grown in a small size (80–600 nm) with a specific crystallographic orientation and provide an excellent test bed for validating the GPFE theory. One way to experimentally measure this energy is using the tensile testing approach as the measured stress-strain curve necessarily contains the energetics corresponding to the defect generation Based on this argument and considering the small dimensions of the NWs, the in-situ tensile testing of Al NWs inside a transmission electron microscopy (TEM) system is an attractive method for resolving the dissipated energy associated with DT from the measured mechanical response, while simultaneously capturing the instant of the twin formation. This was achieved by first deriving an equation that enables the estimation of the twin formation energy from the GPFE curve obtained for a perfect Al crystal using the first-principles calculations
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