Materials Science Forum Vols. 702-703

Abstract: Commercial grade AA8090 Al–Li alloy sheet contained three layers of distinct microstructural features along thickness direction. The surface layer contained well recrystallized equiaxed grains with higher fraction of T {4 4 11}, Cu {1 1 2}, H {0 0 1} and CH {0 0 1} texture components whereas middle layer contained unrecrystallized elongated grains with higher fraction of brass {0 1 1}, CG {0 2 1} and goss{0 1 1} texture components. Superplastic forming of the separated surface and middle layers was carried out at constant pressure. Microstructure and texture evolution was studied at different location of the formed bulge. The extent of texturing or anisotropy was calculated from standard deviation of texture estimated normal anisotropy (R) values, R_stdev. At all conditions, in both the surface and middle layers, the texture randomization was found to be more at the apex than that at the edge of the bulge. The overall reduction in texturing was predominantly accompanied by weakening in strong texture components and strengthening in the weaker ones.

Abstract: Nanocrystalline Ni and Ni-P alloy with grain size down to 6 nm were processed by pulsed electrodeposition. The as-deposited materials, possessing a strong fiber texture, were tested in tension at different temperatures and strain rates. Both materials exhibited low temperature superplasticity but with significant differences in mechanical characteristics. In comparison with nano-Ni, the nano Ni-P alloy exhibited significant strain hardening in flow behavior and lower superplastic elongations at relatively low strain rates, although the grain size was finer at test temperatures with limited grain growth in nano Ni-P alloy. Texture study as a function of strain and strain rate by bulk X-ray Schultz reflection and electron back scattered diffraction (EBSD) revealed development of cube components {001} and {013} with negligible deformation texture components (Cu or brass type) and limited fraction of low angle grain boundaries (< 10 %) in superplastically deformed samples. The reasons for the formation of cube components and their influence on flow behavior of electrodeposited materials were critically analyzed. Additional microstructural investigation by transmission electron microscopy revealed dislocations movement constrained by intragranular particles, leading to strain hardening and cavitation in the nano Ni-P alloy.

Abstract: The formation of Cube oriented elements in plane strain compressed aluminium has been studied by EBSD for both hot and cold deformations. By following the orientation changes of the same set of 176 grains deformed at 400 °C up to a strain of 1.2 using a split sample, it is shown that about 15% of the grains can break up into several regions of very different orientations, characterized by very large orientation gradients. In particular those grains oriented within about 30° of Cube develop Cube oriented zones in contact with other rolling texture components. Finite element crystal plasticity simulations confirm this mechanism of creation of Cube by plastic deformation. The same type of microstructure can also be observed after heavy cold rolling (strain of 2.3), but at a scale that is much finer by at least an order of magnitude. In this case the micron-sized Cube fragments are located along many grain boundaries or in some particular grains. When the cold deformed sample is annealed, EBSD observations of the same areas reveal that the intergranular Cube fragments are very efficient recrystallization nucleation sites, apparently since they possess mobile high angle boundaries with the local environment.

Abstract: The goal of the present study inspired by previous works on high purity aluminiun was to manufacture aluminium sheets of commercial purity, grade 1050, with a strong cube texture. In this preliminary work on AA1050, sheets which cube volume fraction reaches 65% have been manufactured. Parameters controlling cube orientation development are mainly the solute dragging due to impurities in solid solution and the stored deformation energy. Besides the 85% cold rolling (CR), two extra annealings and a slight cold rolling are introduced in the processing route to increase the cube volume fraction. The cube orientation, whose substructure is equiaxed, is important for its recovery. It develops thanks to the difference of stored energy relative to that of its first neighbors; the slight cold rolling enhances growth of these cube grains.

Abstract: A series of oxygen free high conductivity copper samples with different initial grain sizes, cold rolling conditions and storage times as well as slightly different impurity contents was used to investigate the effects of these initial parameters on the development of cube texture during recrystallization. For rolling reductions of 90% and 95%, cube textures with volume fractions between 3% and 50% were observed. Higher rolling reduction led to a stronger cube texture. Cube texture development is very sensitive to the initial grain size before rolling. In general, fine grained material gives a strong cube texture after recrystallization, and the requirement on fineness of the grain size may vary for materials with different purity. Large sample widening during rolling can largely inhibit the development of cube texture after recrystallization. Neither storage time, nor the slight change in impurity content had large effects in the present investigation.

Abstract: A pure Ni sheet was heavily deformed up to an equivalent strain of 6.4 at room temperature and then annealed to obtain highly Cube textured material, which is a polycrystal subdivided by many low-angle grain boundaries. The highly Cube-oriented sheets were cold-rolled to various reductions up to 90%. It was found that large fraction of Cube oriented grains remained stable in cold-rolling although the orientation is theoretically unstable. The stability of Cube orientation was considered to be associated with the constraint by grain boundaries in the materials.

Abstract: The effect of ultrahigh straining on the evolution of cube texture in high purity nickel (99.97%) processed by Accumulative Roll Bonding (ARB) is investigated in the present study. Fully recrystallized nickel sheet having average grain size of 28 μm is deformed by ARB to the strain levels of εeq=3.2 and εeq=6.4 corresponding to 4 and 8 cycles of ARB processing, respectively, and subsequently annealed at different temperatures. The 8 cycle ARB processed material consistently shows much higher cube volume fraction as compared to the 4 cycle processed material after different annealing treatments. Almost 100% cube volume could be obtained in the 8 cycle processed material after annealing at 800°C. The development of extremely sharp cube texture in the 8 cycle processed material could be attributed to the oriented nucleation of cube grains at early stages of recrystallization and subsequent growth of these grains. The results indicate that ultrahigh straining could be useful for applications requiring near perfect cube texture such as substrates for coated superconductors applications.

Abstract: The cold-rolled pure copper sheets were annealed without and with a high magnetic field of 12T. The results showed that the application of the magnetic field could promote the recovery and recrystallization processes of cold rolled pure copper. The intensity of Cube component in the field treated samples was obviously higher than that in the non-field treated ones at the same annealing temperature.

Abstract: Crystallographic texture analysis is a microstructure characterization technique essential for relating microstructure attributes to the anisotropy of properties in crystalline matter. As such, it is widely used in research as well as in industrial materials and process design. Additionally, texture analysis is also used in industrial applications to monitor the consistency of a process for e.g. the anisotropy in mechanical properties from product to product. This overview outlines the reduction of quantitative texture data for the use in industrial settings.

Abstract: In crystal plasticity models the crystal anisotropy of the yield strength is accounted for by the yield locus. In the present paper the full constraint Taylor model is used to calculate the yield strength anisotropy of a heavily cold rolled and annealed IF steel. In addition to the crystallographically induced anisotropy also the grain shape anisotropy was taken into account. To this purpose a model is presented in which the grain size that appears in the Hall-Petch relation is substituted by an effective grain size that is dependent of the grain-shape morphology and the crystal orientation. The grain shape of a specific crystal orientation is approximated by an ellipsoid volume of which the major axes are obtained from experimental data. The effective grain size of a specific crystal orientation is determined by the intersection of the most active crystal slip plane of this orientation and the ellipsoid volume.