Effects of solute Mg on grain boundary and dislocation dynamics during nanoindentation of Al–Mg thin films

Abstract

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractUsing in situ nanoindentation in a transmission electron microscope (TEM) the indentation-induced plasticity in ultrafinegrained Al and Al-Mg thin films has been studied, together with conventional quantitative ex situ nanoindentations. Extensive grain boundary motion has been observed in pure Al, whereas Mg solutes effectively pin high-angle grain boundaries in the Al-Mg alloy films. The proposed mechanism for this pinning is a change in the atomic structure of the boundaries, possibly aided by solute drag on extrinsic grain boundary dislocations. The mobility of low-angle boundaries is not affected by the presence of Mg. Based on the direct observations of incipient plasticity in Al and Al-Mg, it was concluded that solute drag accounts for the absence of discrete strain bursts in indentation of Al-Mg.

Enhancing dislocation emission in nanocrystalline materials through shear-coupled migration of grain boundaries

“…3a and c). The above results indicate that the dislocation emission process is energetically more favorable, as shear-coupled migration is the dominating process compared with pure normal migration and that the coupled shear (i.e., β 4 0) is able to considerably enhance the dislocation emission in NC materials, which is in good agreement with the existing observations made in experiments [27,[38][39][40], MD and quasicontinuum studies [25,26].…”

“…This result indicates that the coupled shear (i.e., the coupling factor β) plays an important role in enhancing the dislocation activity in nanocrystalline materials, which consist of mostly high-angle boundaries (i.e., ω4 0:26) [1]. This finding provides a possible explanation for the abundant dislocation activity observed in the experiments conducted by De Hosson et al [38,39] and Mompiou et al [27,40] for nano-grained and ultrafine-grained Al during nano-indentation or tensioning where grain boundary motions played a significant role. Since the value of β depends on the specific structure of GBs, the results obtained from Fig.…”

“…[25]). Some experiments carried out by De Hosson et al [38,39] and Mompiou et al [27,40] have also shown that dislocations activity was promoted during the motion of grain boundary in bicrystal or ultrafine-grained metals and that the moving GBs acted as a source of dislocations. Most recently, Ovid'ko and Skiba [41] proposed theoretically that dislocations could emit approximately vertically from a disclinated GB fragment generated by GB sliding or migration.…”

Nanotwin-assisted grain growth in nanocrystalline gold films under cyclic loading

“…3e). When nanotwins T31 and T32 formed in G3, they impinged on the LAGB and transformed local parts of the LAGB into several boundary segments with a larger angle, which are energetically more favourable than the LAGB for GB migration 8,15,37 . The local orientation of a nanotwin T41 in G4 keeps the orientation close to that of T32 in G3 (only 3.4°), and a perfect dislocation on such a LAGB was also found in Fig.…”

“…Furthermore, Rupert et al 4 have experimentally uncovered the shear-stress-driven GB migration behaviour in the aluminium film using the specimens smartly designed with stress and strain concentrators. Until now, the grain growth has been observed under various loading modes including tension 5,6 , compression 7 , nanoindentation 3,8 and cyclic deformation 9,10 .…”