Structural Refinement, Recrystallization and Grain Growth Phenomena in an Accumulative Roll Bonded Nickel Sheet

© 2017 The Authors. The thickness of the lamellar band (LB) structure that is generated in an accumulative roll bonded nickel sheet represents the degree of structure refinement. The LBs reach a saturation in thickness after several roll bonding cycles due to adiabatic heating that balances the dislocations generated during rolling. The thermal restoration process starts with the rearrangement of dislocations and boundary migration. At the initial stages of thermal restoration, LBs with all the orientations in the deformation texture grow by the so-called continuous recrystallization process. However, in the latter stages, growth becomes orientation selective and dominated by S and copper orientations. Finally, grain growth after recrystallization results in the preferred growth of Cube-oriented grains to the full layer thickness of the ARB sheet, thereby generating a strong Cube texture. Thus, grain growth yields a final texture similar to that generated in conventionally rolled and annealed nickel sheets

On the complexities of microband interactions in a cold-deformed goss-oriented Ni single crystal

In this investigation, the three-dimensional nature of microband boundaries was investigated in a Goss-oriented Nickel single crystal. The sample was 30 pct deformed by plane strain compression and then characterized by several advanced techniques including three-dimensional electron backscatter diffraction (3D-EBSD) and transmission electron microscopy (TEM). In the longitudinal section of the sample, microbands were found to exhibit their classical strip-like appearance. However, the microband interfaces contain numerous curved features despite the average inclination of the interfaces closely matching the potential {111} slip planes. The microband boundary irregularities are argued to be the outcome of microband interactions, which are also linked to the orientation spread of deformation structures. Based on the detailed TEM investigation of the dislocation structures associated with intersecting microbands, it is argued that these interactions result in the disintegration and/or dissolution of microband boundary segments. A correlation between microband and cell boundaries was also found

Substructural phenomena in Cu wire bond after laser assisted manufacturing in electronic packaging

© 2019 Elsevier B.V. This paper studies the crystallographic and substructural details in copper wire bonds on integrated circuit chips. Copper is regarded a potential replacement of gold wire bonding technology used in electronic device manufacturing. The innovative manufacturing process adopted in this work involves simultaneous application of laser heat and ultrasonic pressure. The beneficial effects of laser heating are apparent to overcoming the processing challenges associated with high hardness of copper. The application of laser yields columnar gains and grain size gradient. The laser-assisted samples have undergone a different deformation mechanism which is indicated by the non-localized nature of deformation. The dynamic thermal restorations in the laser-assisted sample are obvious

Formation of Highly Misoriented Fragments at Hot Band Grain Boundaries During Cold Rolling of Interstitial-Free Steel

The deformation heterogeneities that form in the vicinity of prior hot band grain boundaries in a 75 pct cold-rolled interstitial-free steel have been investigated by 3D electron backscatter diffraction. Grain boundary-affected regions occupy a large fraction of the overall material volume. The coexistence of several features, such as steep orientation gradients up to 5 deg/µm, high-angle boundary networks, and thin, elongated grain boundary fragments, has confirmed the highly complex nature of these regions. Most notably, these thin boundary fragments were found to be significantly misoriented from any of the deformed grains immediately adjacent to the boundary. Overall, grain boundary regions adopt the so-called ‘deformation banding’ mode of deformations on both the micro (e.g., steep gradients)- and nano (e.g., thin fragments)-length scales. Grain boundary structures comprise the essential features to act as preferred sites for recrystallization. The discovery of numerous thin grain boundary fragments in the deformation microstructure provides a plausible explanation for the origin of recrystallized grains with orientations other than those found within the adjoining deformed grains in the vicinity of grain boundaries; this phenomenon has been commonly observed in texture data for many years but remained unexplained

Through Thickness Microstructural and Texture Inhomogeneity Within Al Layers in ARB-Produced Al-Al(Sc) Layered Composite Sheets

© 2015, The Minerals, Metals & Materials Society and ASM International.Alternatively layered composite sheets of commercially pure (99.8 pct purity) aluminum and an Al-0.3wtpctSc alloy (either in the supersaturated solid solution or age-hardened conditions) were generated through accumulative roll bonding for up to 5 cycles. The transverse sections of the sheets were examined to investigate the microstructure and texture inhomogeneities developed during the rolling process. Electron backscatter diffraction and transmission electron microscopy was used for this investigation. It was found that an inhomogeneous microstructure and texture was developed through the aluminum layers of the sheet thickness. The nature of inhomogeneities changes as the ARB bonding progresses to higher cycles. Microstructural inhomogeneities remain prominent in the first ARB cycle and diminish during the subsequent cycles. Texture inhomogeneities appear in different forms as rolling progresses. High frictional shear forces in the surface and in-plane shear forces across bonding interfaces derive these inhomogeneities

Texture balancing in a fcc/bcc multilayered composite produced by accumulative roll bonding

The high strain deformation and recrystallization behaviour of a Fe/Ni multilayered composite sheet fabricated by accumulative roll bonding has been investigated. The comparable initial hardness and subsequent strain hardening behaviour of the Ni and Fe layers reduces the flow compatibility related challenges at the bonding interfaces, thereby generating parallel layers of uniform thickness during rolling to true strains up to 4.18. Typical body centred cubic (α- and γ-fibres) and face centred cubic (β-fibre) rolling textures were generated in the Fe and Ni layers, respectively. During annealing at 700 °C, recrystallization takes place homogenously in the Ni layers but commences initially by particle stimulated nucleation at oxide debris present at the interface of adjacent Fe layers. After recrystallization, the texture of the Ni layers is similar to the starting material prior to ARB, but considerable texture modification occurs in the Fe layers. For both metals, oriented growth of nucleated grains has the greatest influence on the final annealing textures, which generates the classic Cube texture in Ni and a {511} texture in Fe. While these final textures of the individual Fe and Ni layers are not conducive to good formability, texture-based Schmidt factor calculations of the combined layers show an overall balance in texture components that points to a reduction in planar anisotropy. The ability to fabricate multilayered textured sheets by this route is a promising way of controlling the anisotropy of both strength and ductility