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

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

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