Exploring the Limit of Dislocation Based Plasticity in Nanostructured Metals

A twofold decrease to an unexplored scale of 5 nm was produced in Cu by applying a large sliding load in liquid nitrogen. Statistical and universal scaling analyses of deformation induced high angle boundaries, dislocation boundaries, and individual dislocations observed by high resolution electron microscopy reveal that dislocation processes still dominate. Dislocation based plasticity continues far below the transition suggested by experiment and molecular dynamics simulations, with a limit below 5 nm. Very high strength metals may emerge based on this enhanced structural refinement.

Figure 1

Nanostructure produced by friction viewed in cross section by HREM. Tracings of the boundaries are overlaid in white. The horizon is parallel to the shear direction and the vertical to the shear plane normal. The scale marker is 10 nm.

Figure 2

Cumulative distribution of $D^{\mathrm{GNB}}$ boundary intercept spacings.

Figure 3

Distribution of boundary misorientations for $D_{\mathrm{av}}^{\mathrm{GNB}}=5.2\mathrm{nm}$ in Cu deformed by friction.

Figure 4

Nanostructure produced by friction viewed in cross section by HREM. The enlarged inset shows a glide dislocation marked with a Burgers circuit of black dots; the arrow indicates its position in the central nanocrystal. Tracings of the boundaries are overlaid in white. The horizon is parallel to the shear direction and the vertical to the shear plane normal. The scale marker is 5 nm.

Figure 5

Probability distribution of nanometer scale boundary spacings produced by friction normalized by the average spacing compared to distributions at a larger scale in rolled nickel. Friction, solid circles: $D_{\mathrm{av}}^{\mathrm{GNB}}=5.2\mathrm{nm}$; triangles: Ni 70% reduction, $D_{\mathrm{av}}^{\mathrm{GNB}}=280\mathrm{nm}$; squares: Ni 98% reduction, $D_{\text{av}}^{\text{GNB}}=133\mathrm{nm}$. Rolling data from Ref. [11].