Shape Memory Effect in Cu Nanowires

Abstract

A rubber-like pseudoelastic behavior is discovered in single-crystalline face-centered-cubic (FCC) Cu nanowires in atomistic simulations. Nonexistent in bulk Cu, this phenomenon is associated primarily with a reversible crystallographic lattice reorientation driven by the high surface-stress-induced internal stresses due to high surface-to-volume ratios at the nanoscale level. The temperature-dependence of this behavior leads to a shape memory effect (SME). Under tensile loading and unloading, the nanowires exhibit recoverable strains up to over 50%, well beyond the typical recoverable strains of 5-8% for most bulk shape memory alloys (SMAs). This behavior is well-defined for wires between 1.76 and 3.39 nm in size over the temperature range of 100-900 K.

Microstructure and mechanical properties of constrained shape-memory alloy nanograins and nanowires

“…For thin films, 3,4,5,6 nanowires, 7,8 and nanocrystals 9,10 the geometric constraints will have an impact on martensite formation. Recently, Frick et al 11 experimentally studied the stress-strain behavior of nanopillars of nickel titanium shape-memory alloys (SMA), using nanoindentation tests.…”

Alternating starvation of dislocations during plastic yielding in metallic nanowires

“…Due to the unique mechanical, thermal, electrical and optical properties, materials with nanometer-sized structure have attracted a great deal of interest as potential building blocks in nanoelectronic and nanoelectromechanical devices [1]. Many researchers have demonstrated, through both experiments and analysis, that the structure and properties of nanowires can be quite different from those of bulk materials due to the effect of the large surface to volume ratio [2][3][4][5][6][7][8][9][10][11][12][13][14].Recently, Uchic et al [15,16] and Greer et al [17,18] reported that the plastic deformation behavior of single-crystalline sub-micropillars is dependent on the size of the pillar, even without a deformation gradient. More recently, a ''mechanical annealing" test was used to demonstrate that dislocations can be swept out of the samples through the progressive activation and exhaustion of dislocation sources [19].…”

“…More recently, a ''mechanical annealing" test was used to demonstrate that dislocations can be swept out of the samples through the progressive activation and exhaustion of dislocation sources [19]. These promising results raise an important question: is the size effect still operative when the size of the pillar is reduced to under 10 nanometers?Despite many efforts [6][7][8][9][10][11][12][13][14], a quantitative understanding of dislocation flow in nanoscale metals has remained elusive. In particular, the correlation of the dislocation flow with the stress-strain curve is of great interest, for the underlying mechanisms are typically represented by a mechanical response in macroscopic level experiments.…”

“…Despite many efforts [6][7][8][9][10][11][12][13][14], a quantitative understanding of dislocation flow in nanoscale metals has remained elusive. In particular, the correlation of the dislocation flow with the stress-strain curve is of great interest, for the underlying mechanisms are typically represented by a mechanical response in macroscopic level experiments.…”

“…Many researchers have demonstrated, through both experiments and analysis, that the structure and properties of nanowires can be quite different from those of bulk materials due to the effect of the large surface to volume ratio [2][3][4][5][6][7][8][9][10][11][12][13][14].…”