Figure 1

The schematic presentation of in-situ SXRD setup. The longitudinal direction in the figure refers to the direction parallel to the tensile axis, which measures the lattice strain of the planes normal to the tensile axis, whereas the transverse direction measures the lattice strain of the planes parallel to the tensile axis.Reuse & Permissions

Figure 2

Cross-sectional TEM images of (a) nc cobalt and (b) nc nickel. The corresponding insets are the selected area electron diffraction (SAED) patterns of these two materials acquired with a selected aperture diameter of 2.0 $\mu$m (lower left corner). The inset on the lower right corner of (b) is the SAED pattern acquired with a 0.4 $\mu$m diameter aperture. Note the slightly elongated grains in nc nickel.Reuse & Permissions

Figure 3

(a)–(d) The effects of sample-preparation techniques on the surface conditions. (a) and (d) Scanning electron microscopy micrographs of gauge edges of nc cobalt and nc nickel cut by EDM, respectively. Note the sizable pitting on the surfaces of both samples. The inset in (a) is a lower-magnification image of the side surface of nc cobalt after cutting, showing a high concentration of pitting voids. (b) Scanning electron microscopy image of nc cobalt after PLC. No pitting was observed. (c) and (f) FIB ion-channeling images of nc cobalt and nc nickel after PLC, respectively, showing grain-growth gradient layers. (g) A higher-magnification FIB ion-channeling image of grain-growth layer in nc nickel after laser cutting. (e) FIB ion-channeling image of nc nickel after EDM-cutting. No clear grain-growth layer was observed. A couple of large grains are accentuated inside the rectangle on the upper right corner. Note that all the samples in (a)–(f) are oriented in the same direction (i.e. 60°-tilted view), with the cutting edge on the top side of the images. In (g), the cutting edge is located at the left-hand side of the image.Reuse & Permissions

Figure 4

Tensile engineering stress-strain curves of (a) nc cobalt and (b) nc nickel tested in the strain rate range of 1 × 10${}^{-7}$ to 1 × 10${}^{-1}$ s${}^{-1}$ and two different temperatures (i.e. RT and 77 K).Reuse & Permissions

Figure 5

A logarithmic plot to estimate the strain-rate sensitivity ($m$) of (a) nc cobalt and (b) nc nickel.Reuse & Permissions

Figure 6

Scanning electron microscopy fracture micrographs of (a) nc cobalt tested at 1 × 10${}^{-4}$ s${}^{-1}$ and RT, (b) nc cobalt tested at 1 × 10${}^{-4}$ s${}^{-1}$ and 77 K, (c) cg cobalt tested at 1 × 10${}^{-4}$ s${}^{-1}$ and RT, (d) nc nickel tested at 1 × 10${}^{-4}$ s${}^{-1}$ and RT, (e) nc nickel tested at 1 × 10${}^{-4}$ s${}^{-1}$ and 77 K, and (f) cg nickel tested at 1 × 10${}^{-4}$ s${}^{-1}$ and RT.Reuse & Permissions

Figure 7

Tensile engineering stress-strain curves of nc cobalt annealed at different temperatures.Reuse & Permissions

Figure 8

The root-mean-squared (RMS) strains of nc nickel as a function of loading-unloading cycles at the strain rate of (a) 4 × 10${}^{-6}$ s${}^{-1}$ and (b) 3 × 10${}^{-4}$ s${}^{-1}$, respectively.Reuse & Permissions

Figure 9

The longitudinal residual lattice strains of (a) (200) planes of nc nickel and (b) (110) planes of nc cobalt as a function of the macroscopic plastic strain, acquired at two different strain rates.Reuse & Permissions

Figure 10

The USAXS results obtained for five independent nickel samples with (a) the scattering intensity plotted as a function of the scattering factor ($q$) and (b) the calculated void size distribution using a maximum entropy algorithm. We note from our experiments that the void size distribution is relatively sensitive to the synchrotron beam location relevant to the necking region and the shape assumption during the modeling. Therefore, the plots in (b) do not offer absolute value comparisons between samples.Reuse & Permissions

Figure 11

The hardness as a function of rolling strain for nc cobalt at RT. The inset is the converted true flow stress vs true strain in nc cobalt during the rolling process.Reuse & Permissions

Figure 12

Hall-petch type graphs of monolithic nickel with the data from the literature and our work. Two linear fitting curves were calculated from these data with a respective HP slope of 13.33 and 6.49 GPa/nm${}^{-1/2}$. The solid symbols are data obtained directly from tensile tests, the majority of which are found lying underneath the HP fitting curves as accented inside the ellipse.Reuse & Permissions

Figure 13

A survey of Vickers hardness ($H_v$) vs the yield stress (${\sigma }_y$) and Vickers hardness vs the ultimate tensile stress (${\sigma }_{\mathrm{uts}}$) ratios of nc nickel and nc cobalt.Reuse & Permissions

Figure 14

The numerical calculation of the Tabor relationship for nc nickel, assuming different strain-hardening exponents and different grain sizes. See the text for detailed discussions.Reuse & Permissions

Figure 15

A schematic of necking geometry and stress analysis in thin-sheet samples ($W/T\gg 1$).Reuse & Permissions