Dislocation Dynamics in Nanocrystalline Nickel

It is believed that the dynamics of dislocation processes during the deformation of nanocrystalline materials can only be visualized by computational simulations. Here we demonstrate that observations of dislocation processes during the deformation of nanocrystalline Ni with grain sizes as small as 10 nm can be achieved by using a combination of in situ tensile straining and high-resolution transmission electron microscopy. Trapped unit lattice dislocations are observed in strained grains as small as 5 nm, but subsequent relaxation leads to dislocation recombination.

Figure 1

TEM observations of the typical microstructure in the as-deposited nanocrystalline nickel films. The bright field TEM micrograph (a) and dark field TEM micrograph (b).

Figure 2

(a) HREM micrograph of a thin area freshly formed by deformation. The white $\mathsf{T}$’s and dark arrowheads indicate the position of a trapped unit lattice dislocation in the grain interior. Grain boundaries have been delineated by dark lines. (b) IFFT of the area framed with the dark box in (a). The Fourier-transformed image shown as an inset indicates that the electron beam is close to the 110 zone axis of the grain. (c) IFFT of the area framed with the white box in (a).

Figure 3

Dynamical HREM observations of the microstructure evolution of a strained area during the stress relief. The positions of the dislocation cores have been indicated by $\mathsf{T}$’s. (a) $t=0$, (b) $t=86\mathrm{s}$, (c) IFFT of (a), and (d) IFFT of (b).