Materials Science Forum Vols. 495-497

Abstract: The crystallography of recrystallization nucleation has been investigated in channel-die deformed pure aluminium bicrystals with {100}<011>/{110}<001> and {100}<001>/{110}<001> orientations. The new grain orientations and misorientations were followed by systematic local orientation measurements using SEM and semi-automatic measurements in a TEM. In particular, orientation mapping combined with in-situ sample heating was used to investigate the formation and growth of new grains and their crystallographic orientation changes at very early stages of recrystallization. Grain boundary migration and ‘consumption’ of the as-deformed areas was always favoured along directions parallel to the traces of the {111} slip planes that had been most active during deformation. The orientations of the first formed nuclei were misoriented with respect to the orientations identified within the neighbouring deformed areas by α(<111>, <112>, or <100>)relations.

Abstract: Relative grain boundary energy as a function of misorientation angle was measured in a cube-oriented, 120 µm-thick Al foil and in a <111> fiber-textured, 1.7 µm-thick Al film using a multiscale analysis of the grain boundary dihedral angles. For the Al foil, the energies of low-angle boundaries increased with misorientation angle, in good agreement with the Read-Shockley model. For the Al film, two energy minima were observed for high-angle boundaries. Grain growth was studied in 25 and 100 nm-thick films that were annealed at 400 °C for a series of times in the range of 0.5 to 10 h. For the 100 nm-thick film, grains approximately doubled their size (equivalent circular diameter) before grain growth stagnated. The steady-state distributions of reduced grain area for two-dimensional, Monte Carlo Potts and partial differential equation based simulations showed excellent agreement with each other, even when anisotropic boundary energies were used. However, the simulated distributions had fewer small grains than the experimental distributions.

Abstract: A 12-Tesla magnetic field was applied during the transformation from austenite to ferrite and then pearlite in a medium plain carbon steel at two different cooling rates. Results show that when cooling is slow, the magnetic field shows an effect of promoting proeutectoid ferrite grains to grow along the field direction that results in an elongated grain microstructure. However, when cooling is fast, the magnetic field mainly shows an effect of reducing the amount of low angle misorientations and increasing the amount of CSL boundaries. In addition, the magnetic field exhibits a slight enhancement of the <001> texture component in the direction that is perpendicular to the field direction (TFD).

Abstract: The influence of Mn on the surface texture formation through a®g®a transformation was investigated. After the a®g®a transformation, a weak texture was formed at the surface of ultra low carbon cold-rolled sheet steel without Mn. In contrast, a sharp <100>//ND cube texture was observed in Mn alloyed ultra low carbon steel. In order to interpret the effect of Mn two alternative mechanisms were considered : (i) one assumption attributes the occurrence of the specific surface texture to the effect of outer-surface energy (ii) and according to an alternative hypothesis the release of elastic work parallel to ND in the surface area is responsible for the observed <100>//ND surface texture.

Abstract: In high purity (4N) Al containing 50 ppm Cu, very strong cube textures can be developed by cold rolling 98 % and annealing at 500 °C. The orientation density in this material amounted to as much as 220 times random, i. e. about 3 times stronger than that observed in standard 4N Al. It is expected that the origins of cube textures should be most unambiguously clarified by using this material. Commercial hot bands of this materials were cold rolled 98 % to the thickness of 132 μm and isothermally annealed at 230 °C. Detailed EBSP analyses were made both on the rolling plane and on the longitudinal section at each stage of annealing. It was found that in the hot band of this high purity Al, cube orientations were mostly rotated away into other orientations due to low temperature hot rolling with high rolling reductions. Therefore, regions having cube orientations were very few. They were not present in the form of so called cube bands, which had been reported in previous investigations, but in the form of isolated, rather equi-axed recrystallized grains. After 98 % cold rolling, these remaining cube regions were fragmented, and further rotated away into other orientations, so that only very few cube oriented regions were observed in the cold rolled materials. However, it was from such deformed cube oriented regions that the most potential exact cube recrystallized grains were formed. They were nucleated much earlier and grew much faster than grains of other orientations.

Abstract: In order to study the influence of mechanical stress fields on the kinetics and texture evolution of grain growth, experiments were performed on high purity aluminium. Samples were annealed under the influence of different mechanical stresses. The temporal evolutions of grain sizes and of macrotexture were analysed in ependence on the applied stress. The results show that mechanical stresses can change the kinetics of grain growth and slow down the increase in the grain size. Also effects on the texture evolution were observed and shall be discussed.

Abstract: A critical point in the understanding of recrystallization textures is the development of crystallographic orientations of the nuclei. Here an issue, which has been debated much recently [eg. 1], is if nuclei have orientations identical to those of the deformation microstructures from which they originate or not. Traditional nucleation mechanisms like strain induced boundary migration [2] and particle stimulated nucleation [3] operate with nuclei orientations identical to the “parent”deformation microstructure. This is also what is commonly incorporated in recrystallization modeling. However, a number of studies have found recrystallization nuclei in orientations that were not expected from measurements on deformed structures. Some of these results are reviewed and discussed in this paper, and new in-situ results obtained by the 3 dimensional X-ray diffraction (3DXR) method are presented.

Abstract: The stored energy of two cold rolled IF-Ti steels is calculated using finite element method from an EBSD microstructure. Because the thermo-mechanical treatments are different for the two materials, the parameters of the behaviour law used in the simulation and identified using a polycrystalline model and an inverse method from experimental results are also different. Their variation is due to the number of experimental tests taken into account for their identification and obviously to the thermo-mechanical path. The stored energy is mainly influenced by Lu which represents the mean free path of the mobile dislocations gliding on the system u and which is expressed as a function of a K material parameter. Using one tension test, the experimental stored energy values estimated from neutron diffraction measurements can be reproduced only for a material parameter K fixed.

Abstract: The first steps of recovery and recrystallization in an IF-Ti steel after 35% deformation by uniaxial tension have been studied by Electron Back Scattered Diffraction (EBSD), Orientation Imaging Microscopy(™) (OIM) and Transmission Electron Microscopy (TEM). Two types of substructure are created after tensile strain: diamond shaped cells for the {111}<110> component and equiaxed cells for {001}<110> component. The recovery is by the decrease of dislocation density inside cells, the refinement of the cell walls, the vanishing of the cell wall, the cell coalescence and the cell growth. Recrystallized grains developed by two main recrystallization mechanisms: the “generalized recovery” and the “bulging”. Both mechanisms are based on continuous growth of subgrains followed or not by the migration of the prior grain boundaries.

Abstract: In this work, EBSD (Electron Back Scattered Diffraction) measurements have been performed on deformed, partially and fully recrystallized cold rolled copper to 70 and 90 % reduction. The twin fraction as well as its existing relation with the parent crystallographic orientation has been followed in relation with respect to the recrystallized fraction. It has been shown thanks to this quantitative analysis that annealing twinning is more active when recrystallization nuclei slowly develop. The experimental observations are briefly discussed according with the twins selection principles [1].