In situ atomic-scale observation of grain size and twin thickness effect limit in twin-structural nanocrystalline platinum

Abstract

Twin-thickness-controlled plastic deformation mechanisms are well understood for submicron-sized twin-structural polycrystalline metals. However, for twin-structural nanocrystalline metals where both the grain size and twin thickness reach the nanometre scale, how these metals accommodate plastic deformation remains unclear. Here, we report an integrated grain size and twin thickness effect on the deformation mode of twin-structural nanocrystalline platinum. Above a ∼10 nm grain size, there is a critical value of twin thickness at which the full dislocation intersecting with the twin plane switches to a deformation mode that results in a partial dislocation parallel to the twin planes. This critical twin thickness value varies from ∼6 to 10 nm and is grain size-dependent. For grain sizes between ∼10 to 6 nm, only partial dislocation parallel to twin planes is observed. When the grain size falls below 6 nm, the plasticity switches to grain boundary-mediated plasticity, in contrast with previous studies, suggesting that the plasticity in twin-structural nanocrystalline metals is governed by partial dislocation activities.

In situ atomistic mechanisms of detwinning in nanocrystalline AuAg alloy

“…This is also consistent with the rate of detwinning resulting from ITB migration (red circle) being faster than the other two detwinning mechanisms. These results indicate that the dislocation-CTB interaction can delay the detwinning process and contribute to strain hardening, whereas ITB migration can easily occur, which can supply large plasticity [1,7,10,11].…”

“…This GB migration allowed the detwinning process to occur without the need for partial dislocation nucleation from the CTB-GB intersection or the movement of partial dislocations at the ITB. Thus, this type of detwinning process is important in NC metals because GB migration is more easily triggered in small-sized grains [7,12]. During the deformation process, the lattices in G 1 and G 3 exhibited no obvious changes, indicating that there was no obvious out-of-plane rotation or global tilt of the specimen during deformation.…”

“…Face-centered cubic (FCC)-structured metals with grown nanotwins have attracted great interest because of their ultrahigh strength and excellent ductility compared to their twin-free counterparts [1][2][3][4]. Because the mechanical properties of twinstructured metals are directly related to their deformation mechanisms, a large number of studies have been conducted to study the deformation mechanism of twin-structured metals in the last decades [1][2][3][4][5][6][7][8]. It is well established that the strengthening of twin-structured metals results from dislocations intersecting with coherent twin boundaries (CTBs), which was confirmed by both molecular dynamics (MD) simulations and experimental investigations [1,5,6,[9][10][11][12].…”

“…In contrast, for the softening mechanism, in situ atomic-scale observations of the detwinning process have rarely been studied, especially for twinstructured nanocrystalline (NC) metals with grain sizes of 15 nm [3,9,10,[13][14][15][16]. In addition to dislocation-CTB intersection, several MD simulations and experiments have indicated that detwinning can also significantly affect the mechanical properties of twin-structured metals [7,10,11,17]. The atomicscale mechanism of detwinning is crucial, which may provide clues for designing twin-structured metals with high strength and excellent ductility [1,10,[16][17][18][19].…”

Microwave-irradiated novel mesoporous nickel oxide carbon nanocomposite electrodes for supercapacitor application

“…In twin structural nanocrystalline materials, both grain size and twin-thickness decreased to the nanometer scale. Twin thickness significantly affects the deformation model of face-centered cubic structured materials, and it is unclear due to direct atomic-scale observations rarely acquired in experiments [20] . impurity evidence in the composition [21] .…”