Transformation of the Deformation Mechanism from Dislocation-Mediated Slip to Homogeneous Slip in Silver Nanowires

Abstract

The tensile deformation behavior of silver (Ag) wires with nanometer widths (nanowires (NWs)) was observed by in situ high-resolution transmission electron microscopy combined with subnanonewton force measurements. The Young's modulus, strength, and critical shear stress of the Ag NWs were investigated based on the mechanics of materials at the atomic scale. It was found that when the minimum cross-sectional area of the NWs decreased to less than approximately 3.2 nm2, the critical shear stress increased with a decrease in the area. In addition, when the minimum cross-sectional area decreased to less than approximately 0.5 nm2 before fracture, the critical shear stress reached 0.96 GPa, which exceeded the theoretical shear stress of bulk Ag crystals on {1111} along (110). The present results indicate that the deformation mechanism of Ag NWs transformed from dislocation-mediated slip to homogeneous slip. Therefore, it can be concluded that size reduction to nanometer scale leads to a considerable increase in strength.

Transformation from slip to plastic flow deformation mechanism during tensile deformation of zirconium nanocontacts

“…1 (a)–(f), both nanotips separate, leading to slip suppression by the restoring force in the opposite direction of slip 11 . In addition, the contact width decreases to several atoms and slip without introduction of a dislocation occurs, i.e., homogeneous slip, resulting in the critical shear stress of theoretical slip 10 11 12 . As a result, slip is inhibited and Zr NCs begin to elongate toward the tensile force directions, which do not always correspond to primary and comparable slip systems.…”

“…When the grain size of polycrystalline metals is decreased to 10–100 nm, grain boundary sliding and grain rotation govern deformation instead of dislocation-mediated slip 1 2 3 4 5 6 7 . In particular, as the width of deformation region is reduced to several atoms, the deformation mechanism is transformed from dislocation-mediated slip to non-slip manners, i.e., homogeneous slip 8 9 10 11 12 . After the transformation of deformation mechanics, the critical shear stress of nanometer-size metals increases by several tens of times or more in comparison with that of dislocation-mediated slip, e.g., ~1 GPa for silver 11 (Ag) and ~5 GPa for rhodium 12 (Rh).…”

“…In particular, as the width of deformation region is reduced to several atoms, the deformation mechanism is transformed from dislocation-mediated slip to non-slip manners, i.e., homogeneous slip 8 9 10 11 12 . After the transformation of deformation mechanics, the critical shear stress of nanometer-size metals increases by several tens of times or more in comparison with that of dislocation-mediated slip, e.g., ~1 GPa for silver 11 (Ag) and ~5 GPa for rhodium 12 (Rh). Such a transformation is observed in metallic nanocontacts (NCs) with face-centered cubic (fcc) structures 10 11 12 .…”

“…After the transformation of deformation mechanics, the critical shear stress of nanometer-size metals increases by several tens of times or more in comparison with that of dislocation-mediated slip, e.g., ~1 GPa for silver 11 (Ag) and ~5 GPa for rhodium 12 (Rh). Such a transformation is observed in metallic nanocontacts (NCs) with face-centered cubic (fcc) structures 10 11 12 . Since the number of primary slip systems in fcc structure metals is 12, slip along equivalent slip systems can occur easily 13 ; deformation via slip continues until the size is reduced to less than several nanometers and subsequent fracture occurs, regardless of whether the dislocation is mediated.…”

“…Conversely, the primary slip system of metals with hexagonal-closed packed (hcp) structure is limited to only three equivalent systems on basal planes 13 . In addition, the rotation of the deformation regions of NCs is suppressed since the region is fixed by two adjacent rigid tips 11 . Atomic-size contacts of zinc (Zn) with an hcp structure show unstable melting-like behavior, related to different break conductance features from NCs of other metals 14 .…”