U. Chakkingal

Bio: U. Chakkingal is an academic researcher from Rensselaer Polytechnic Institute. The author has contributed to research in topic(s): Recrystallization (metallurgy) & Die (manufacturing). The author has an hindex of 1, co-authored 1 publication(s) receiving 18 citation(s).

The effects of die angle on texture and annealing response of ETP copper wire

Abstract: As-annealed, 2.47 mm ETP copper wire was drawn in five passes to 1.45 mm using carbide dies with nominal included angles of 8, 16 and 24 degrees. A single die, low speed drawing block was used, and the lubricant was fat-based and water soluble. Annealing was undertaken in a box furnace, for six minutes at temperatures ranging from 185 to 230°C. Annealing response and texture evolution were assessed by way of tensile tests, microhardness measurements and x-ray diffraction. Redundant strain accumulation was projected by way of deformation zone geometry, or Δ, analysis. The as-drawn wire reveals volumes of (111) and (200) fiber texture, as well as a significant volume of essentially randomly oriented grain structure. The ratio of (111) to (200) texture decreases as die angle increases. Increases in die angle and related redundant strain promote the development of random orientation and reduce the sharpness of the (111) and (200) texture components. Increases in die angle and related redundant strain also lower the annealing temperature range and cause non-uniform recrystallization, presumably due to redundant strain and texture gradients. The as-annealed 1.45 mm wire displays a large volume of randomly oriented grain structure for all three die angles. In the case of the as-annealed wire, increases in die angle are associable with a decrease in the volume percent of (111) fiber texture, a decrease in the sharpness of the (200) fiber texture, and an increase in randomly oriented grain structure.

The evolution of annealing textures in 90 Pct drawn copper wire

Abstract: An electrolytic copper rod was drawn in 24 passes to a 90 pct reduction in area and subsequently annealed under various conditions. The global texture of the drawn wire, as measured by X-ray methods, showed a fiber texture approximated by a strong 〈111〉 and a weak 〈100〉 component. However, its microtexture, as measured by electron backscattered diffraction (EBSD), indicated that the major 〈111〉+minor 〈100〉 duplex fiber texture was dominant only in the center region, while a relatively diffuse texture developed with a somewhat higher density of orientations having a 〈11w〉//wire axis in the middle and surface regions. The inhomogeneous texture in the as-deformed wire gave rise to an inhomogeneous microstructure and texture after annealing. When annealed at 300 °C or 600 °C for 3 hours, the wire developed a duplex fiber texture consisting of major 〈100〉+minor 〈111〉 components in the center region, a strong 〈100〉 fiber texture in the middle region, and a weak texture consisting of 〈111〉 and 〈100〉 components with the 〈111〉 component being slightly stronger in the surface region. When the drawn wire was annealed at the high temperature of 700 °C, the texture at short annealing times was similar to that of the wire annealed at the lower temperatures of 300 °C and 600 °C for 3 hours, but prolonged annealing gave rise to a texture ranging from the 〈111〉 to 〈112〉 components due to abnormal grain-growth that started in the surface region. The recrystallization texture consisting of the major 〈100〉+minor 〈111〉 components was explained by the strain-energy-release maximization (SERM) model, in which the recrystallization texture is determined such that the absolute maximum principal stress direction due to dislocations in the deformed state is along the minimum elastic-modulus direction in recrystallized grains. On the other hand, the abnormal grain-growth texture was attributed to grain-boundary mobility differences between differently oriented grain.

Dependence of texture evolution on initial orientation in drawn single crystal copper

Abstract: The evolution of fiber texture in the drawn single crystal copper wires with initial orientations of , and parallel to axis direction has been studied via electron backscattering diffraction. During cold drawing process, grain subdivision takes place in the , and single crystals. At high strains, a mixture of and fiber textures forms, but due to uneven shear strain, the distribution of the and fiber textures is inhomogeneous along the radial direction of wires. The fiber texture component is located in the centre of wires and is near the surface. Although grain subdivision appears in the , and single crystals, the stability of the three initial orientations is different. The initial orientations of and are more stable than . is stable at low strains while becomes stable at high strains.

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.

Characterization of microstructure evolution after severe plastic deformation of pure copper with continuous columnar crystals

Abstract: Pure copper bar with continuous columnar crystals was fabricated by continuous unidirectional solidification. The bar with orientation preference along [0 0 1] exhibited novel plastic deformation ability with total true strain over 13.5 during rolling and drawing at room temperature without annealing. Microstructure analysis and in situ observation of tensile test were performed to investigate the mechanism of plastic deformation. Results exhibit that the novel plastic deformation ability of copper bar is beneficial from the absence of transverse grain boundary as well as small angle grain boundary of the continuous columnar microstructure. The existence of cell structure, recrystallization and deformation twin leads to grain rotation during deformation and enhances the orientation preference of the continuous columnar crystals, enabling copper bar a high ability for further deformation.

Unusual Young׳s modulus behavior in ultrafine-grained and microcrystalline copper wires caused by texture changes during processing and annealing

Abstract: Effect of annealing on the dynamic Young׳s modulus E of ultrafine-grained (UFG) and microcrystalline (MC) copper obtained by combined severe plastic deformation (SPD) including repeated hydrostatic extrusion and drawing (UFG copper) or only repeated drawing (MC copper) is investigated. It is established that the Young׳s modulus in the SPD-prepared UFG and MC samples exceeds that in the coarse-grained fully annealed (CGFA) samples by 10% to 20%. Subsequent isothermal annealing at elevated temperatures between 90 and 470 °С leads to a sharp decrease of the Young׳s modulus for annealing temperatures above 210 °С. After annealing at 410 °С, the value of E reaches its minimal value that is 35% lower than E in CGFA samples (total change in E is about 50% of the initial value). Further annealing at higher temperatures leads to some increase in the Young׳s modulus. It is shown that the unusual behavior of the Young׳s modulus is caused by the formation of the 〈111〉 axial drawing texture in the SPD-treated samples which is replaced by the 〈001〉 annealing texture during the post-SPD heat treatments.