Materials Science Forum Vols. 558-559

Abstract: The effect of crystal orientation on the recovery and recrystallization of cold-rolled Ni (99.96% purity) has been investigated. Particular attention was paid to the annealing response of regions with either the Copper (C), Brass (B) or S rolling texture orientations. Samples with an initial average grain size of approx. 500μm were deformed to strains of up to εvM = 4.5. As a result of the large initial grain size, even after high rolling reductions it is possible to find sufficiently large regions of material with similar crystal orientation to analyze the recovery and recrystallization behaviour as a function of crystal orientation. Microstructural investigations were carried out in the scanning electron microscope using both electron channeling contrast and electron backscatter diffraction orientation mapping. Both the S and C orientation regions exhibit a heterogeneous microstructure containing bands of localized deformation. The presence of volumes surrounded by high angle boundaries in these regions strongly influences both the recovery and recrystallization behaviour of the material. Twinning was observed also to play an important role in the generation of recrystallized grains, with twin chains of up to 3 generations being observed.

Abstract: The softening process consists of recovery and recrystallization. Despite the significant effect of recovery on the softening, recovery has not enjoyed the attention as much as recrystallizaion has mostly due to difficulties in the microstructural characterization of recovery. The present study introduced GOS qualitatively and quantitatively to gauge the microstructural evolution occurring during annealing. Then the GOS analysis was applied to discern alloying effects on recrystallization in hot deformed Al-Cu-Mg alloys. Recovery seems accountable for the retardation of recrystallization in the Mn containing alloys. By adding Zr to Al-Cu-Mg-Mn, recrystallization could be further inhibited.

Abstract: Variations in microstructure and mechanical properties of ZK60 alloy sheets were investigated with aging time. ZK60 alloy sheets with a thickness of 1mm were prepared from a casting ingot followed by homogenization and warm-rolling. Artificial aging process after solution heat treatment (T6) affected both hardness variations and precipitates distributions with aging time. Hardness variations were related to precipitates, i.e. rod-shaped ( 1 β ′ ) or disc shaped ( 2 β ′ ) particles. Rod-shaped ( 1 β ′ ) precipitates mainly consist of Mg and Zn without Zr.

Abstract: Texture and microstructure of gold sheet were investigated during deformation and subsequent annealing. The Brass, S and Copper (β-fiber) orientations are closely connected together in the deformed microstructure. Recrystallization texture also was examined during isothermal annealing at 500°C with reduction in area. Initial rolling textures with rotated cube and β-fiber resulted in the cube and recrystallized β-fiber orientations after annealing. A two dimensional Monte Carlo (MC) method was used to simulate primary recrystallization in gold sheet. A function of boundary misorientation was introduced to consider anisotropic properties of grain boundary energy and mobility. Stored energy associated with orientations in the deformed grains was evaluated by reconstructing of data measured using electron back-scattered diffraction (EBSD). The nucleation at an initial stage of recrystallization was found at the high angle grain boundaries (HAGBs) and grain interiors. The main texture components obtained by the simulation were similar to those obtained experimentally except cube component.

Abstract: A modified two dimensional (2-D) Monte Carlo (MC) technique was used to simulate primary recrystallization in automotive steels containing fine particles. In order to consider anisotropic properties of grain boundary energy and grain boundary mobility, functions of boundary misorientation were introduced. Orientation-dependent stored energy developed in 80% cold-rolled interstitial free (IF) sheet steel was evaluated by reconstructing of data measured using electron back-scattered diffraction (EBSD) analysis. A subgrain method based on subgrain structure is used for quantitative analysis of the stored energy. The simulation reveals that particles affect evolution of microstructure during recrystallization. The simulation provided a theoretical foundation for understanding effect of particles on the final microstructures and crystallographic textures.

Abstract: Oxygen-free high conductivity copper was subjected to room temperature equal channel angular extrusion of 8 passes using route Bc. The resulting ultra-fine grain copper was then rolled to thickness reductions of up to 96.5% at liquid nitrogen temperatures. Annealed coarse grained copper was rolled to the same strain at room temperature for comparison. Samples from the two routes were isochronally and isothermally annealed, and the microstructure and texture evolution studied by electron back scattered diffraction and x-ray diffraction. Annealing of the ultrafine grained copper led to the development of a strong rotated cube texture from a texture in the rolled material dominated by the Brass component. In contrast the more commonly observed cube texture was found after annealing of the coarse-grained sample. Accompanying the rotated cube texture was the development of a large fraction of boundaries with rotation angle/axis close to 60° <111>.

Abstract: Primary recrystallization textures were examined in the 84% and 95% cold-rolled boron-free Ni3Al single crystals with a Goss texture using the electron backscatter diffraction method. It was found that the main components of the textures in the specimens heat-treated at 873K/0.5h had a 40° rotation relationship about <111> to the original, Goss texture. All the eight variants of 40°<111> rotated grains existed. However, the number density is not even but dependent on whether the rotation axis is identical to the normal of slip planes activated during the prior cold rolling. The ratio of the number density among the variants was same in both the 84% and 95% cold-rolled foils. Based on these results, the formation of these 40°<111> rotated grains was explained assuming the modified multiple twinning mechanism where the annealing twinning occurred at the activated slip planes, followed by the subsequent twinning.

Abstract: The structure and properties of oxygen-free copper (99,98%) were studied after different types of severe plastic deformation (SPD): equal-channel angular pressing (ECAP), multiaxial deformation (MD), and accumulative roll bonding (ARB) as a function of the strain at room temperature (to a true strain of 30-40). The SPD facilitates the formation of submicrocrystalline structure with a grain size of 200-250 nm and predominantly high angle boundaries (83-94%). ECA pressing leads to the formation of the most uniform submicrocrystalline structure.The strength characteristics increase with increasing strain and reach the steady stage at ε ≈ 5. At the steady stage, UTS = 460-480 MPa at ARB, and MD, while UTS at ECAP is somewhat lower, 430-440 MPa. The smallest "steady" values EL = 4 - 5% were obtained in the case of ARB, and the maximum EL = 18% was obtained at MD.

Abstract: It is well known that the deformation and recrystallisation of metals and alloys are accompanied by changes in texture and microstructure. These changes can lead to anisotropy in metal flow and affect the formability of sheet metals. Therefore, a significant amount of research on the development of textures and the principles governing them has been conducted in recent years. One of the most important factors contributing to the texture development of materials is the initial grain size. Unlike other factors such as stacking fault energy, strain and deformation temperature, relatively little work has been carried out on the effect of grain size on texture development, even though a considerable understanding exists regarding the effect of grain size on work hardening and recrystallisation kinetics upon annealing. Hence, this research describes the effect of the initial hot band grain size on the development of texture during cold rolling and subsequent annealing.

Abstract: The isochronal annealing behavior of nanostructured commercial purity aluminium (AA1100 and AA1200) following either cold – rolling or accumulative roll bonding up to an ultra high strain of εvM = 6.2 (99.5% reduction in thickness) has been studied via hardness testing and by a microstructural investigation. A large effect of rolling strain is observed on the recovery at temperatures below approx. 200 °C. At higher temperatures an assessment of the changes in hardness and microstructure leads to a characterization of the annealing process as one of conventional (discontinuous) recrystallization.