Papers by Keyword: Microshear Bands

Abstract: Compression tests were performed on Fe-3%Si specimens with few grains. The deformation microstructure and microtexture were investigated by electron backscatter diffraction (EBSD) and related to the initial crystal orientation and grain boundary characteristics. Groups of microbands were found that are characterised by a periodic change in crystal orientation, shear at the grain boundary, and the formation of new grains. It is supposed that these microband groups represent an early stage of microshear band development.

Abstract: A Goss-oriented single crystal was cold rolled up to 89 % thickness reduction, and subsequently annealed at 550°C or 850°C. During deformation most of the initially Goss-oriented material rotated into the two symmetrical {111}<112> orientations. In addition, Goss regions were observed related to microbands or microshear bands. Goss regions in microshear bands formed during straining, whereas Goss regions between microbands were retained from the initial Goss orientation. The recrystallisation texture for annealing temperatures of both 550°C and 850°C is characterised by a Goss texture. However, the origin of the Goss recrystallisation nuclei appeared to be different for the different annealing conditions. In the material annealed at 550°C, the Goss texture originated from the Goss regions in the microshear bands. In contrast, for an annealing temperature of 850°C, the Goss grains between the microbands are likely to form recrystallisation nuclei.

Abstract: High strain rates have a similar influence to large deformations on the refinement of microstructure. In both cases, at large strains and high deformation rates, a strong tendency to form microbands is observed. It was found, that the width of the microbands is very sensitive to changes of the deformation parameters. It has been observed particularly, that in severely deformed materials, the width of the microbands is reduced to nanometric dimensions. Hydrostatic extrusion, which has been used in for the deformation of copper in the current work, strain rates exceeding 2 1 3.84 10 − ⋅ ε = × s were employed. In all the samples investigated, numerous microbands were found in the microstructure. The width of microbands varied from 20 to about 400 nm. Thus, the width of some of the microbands exhibited dimensions typical of nanometric materials. Additionally, a special feature was the appearance of large areas of subgrains with an average dimension of about 200 nm. These areas were identified as recrystallized dynamically, or post-dynamically. Large misorientations were found between the microbands and the surrounding “matrix’. Such misorientation facilitates the formation of high angle boundaries, which in turn contribute to the changes of microstructure and mechanical properties. The mechanism for the creation of high misorientation in the microband areas is probably different from that operating during the process of dynamic recrystalization. The results confirm the possibility of obtaining a nanometric structure at lower deformation, but at higher strain rates.