Effects of size and geometry on the plasticity of high-strength copper/tantalum nanofilamentary conductors obtained by severe plastic deformation

Abstract

Copper-based high-strength nanofilamentary wires reinforced by tantalum nanofilaments were prepared by severe plastic deformation (repeated hot extrusion and cold drawing steps) to be used in the windings of high-pulsed magnets. This application requires a complete characterization of the microstructure and the strength and their relationship for further optimization: after heavy strain, the Cu matrix is nanostructured and the Ta nanofilaments develop a strong ribbon-like shape resulting in an early microstructural refinement. The macroscopic strength is greater than rule-of-mixture predictions as confirmed by nanohardness values. The observed size effect is related to the dislocation starvation in the nanostructured materials combined with the barrier role of Cu/Ta interfaces. The strengthening is lower, however, as expected, because of the distorted ribbon morphology of the Ta filaments preventing them from behaving as nanowhiskers, as Nb fibers do in Cu/Nb wires. This shows that size and geometry play key roles in the plasticity of nanomaterials.

Structure, shear resistance and interaction with point defects of interfaces in Cu–Nb nanocomposites synthesized by severe plastic deformation

“…The bcc Nb nanofilaments in these materials are facetted [21], so Cu-Nb interfaces with the Kurdjumov-Sachs orientation relation (Eqn. 1), but interface planes other than {112}fcc||{112}bcc, may be found.…”

“…Extreme total strains typically larger than 20 are imposed on both the Cu and Nb phases and, as a result, the Cu matrix and the Nb filaments become nanocrystalline with elongated grains in the wire axis direction and cross-section sizes in the 200-400nm and 50-100nm ranges, respectively [21].…”

Emergence of stable interfaces under extreme plastic deformation

“…For single-phase metals, the heavy straining can drive dislocations generated during deformation to organize into low-energy boundary structures (15,16), some of which can be ordered (17) and others disordered (12,(18)(19)(20). Likewise, in heavily drawn two-phase composites, several kinds of bimetal interface structures have been reported, both ordered and disordered (21). Achieving uniformly ordered interfaces in bulk nanostructured metals presents a grand challenge in the design of materials that can be stable in the harsh environments demanded by the next generation of highly energy-efficient systems.…”

“…The individual layer thickness h can be easily refined and controlled with increasing strain (Fig. S1).Previously SPD techniques, like ARB, have been used to make fine-layered material (h = 10-10 2 μm) using large strains but a significant fraction of the interfaces was reported to be disordered and dispersed (18)(19)(20)(21)(22). Here we impose extreme strains, decreasing h by 5-6 orders of magnitude, from 2 mm to 20 nm.…”

The Suppression of Instabilities via Biphase Interfaces During Bulk Fabrication of Nanograined Zr

“…[7][8][9] Realizing these outstanding material properties in structural applications requires methods of fabricating nanomaterials in the bulk form. Over the past few decades, severe plastic deformation (SPD) techniques, such as wire drawing, [10,11] high-pressure torsion (HPT), [12][13][14][15] equal channel angular pressing (ECAP), [16,17] and accumulative roll bonding (ARB), [18][19][20][21][22][23] have been employed to successfully make nanomaterials and nanolayered materials. The last two processes, ECAP and ARB, can potentially produce nanomaterials in sheets and rods in both sizes and quantities suitable for structural applications.…”