Shape memory effects and pseudoelasticity in bcc metallic nanowires

In this paper, using molecular dynamic simulation and ab initio calculations, a novel pseudoelasticity is uncovered in a variety of bcc single crystalline nanowires. Specifically, an initial wire with a < 100 > axis and < 100 > surfaces has been transformed to a new configuration with a < 110 > axis and < 111 > lateral surfaces under uniaxial tensile loading. The loaded < 110 > wire spontaneously reorients back to the original one upon unloading, giving rise to about 41% recoverable strains. The primary deformation mechanisms associated with the reversible lattice reorientation are twinning and detwinning, i.e., forward and backward twin boundary migration on adjacent {112} slip planes. We reveal that the physics underlying the novel behavior in these bcc nanowires is the high propensity for twinning and detwinning, which is characterized as the small ratio of twin boundary migration energy to twin boundary formation energy. Furthermore, the relatively weaker temperature dependence of shape memory effects and larger applicable size range observed in these bcc nanowires render themselves more promising for the future nanotechnology applications. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3506413]