Papers by Keyword: Orientation Imaging Microscopy

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Authors: Hiromi Miura, Sutandyo Andiarwanto, Tetsuo Sakai, John J. Jonas
Abstract: The preferential initiation of dynamic recrystallization (DRX) at triple junctions (TJs) in stainless steel polycrystals was investigated in compression at 1123 K to 1323 K at a strain rate of 2 x 10-4 s-1. Nucleation appeared at TJs at strains as low as 0.1. This strain is only about 1/5 to 1/2 of the peak strain at which DRX is conventionally believed to occur extensively. Furthermore, DRX nucleation was not observed to take place at grain boundaries or in the matrix at this strain. The probability of DRX nucleation at TJs increased monotonically with strain and temperature. It also depended on the angle, y, between the compression axis and the sliding boundary. That is, when the angle, y, approaches 45 degrees, the probability of DRX nucleation at TJs is higher. These results reveal the important role of grain-boundary sliding (GBS) on DRX nucleation at TJs. It should also be noted that more than 90% of the grains nucleated at TJs were twins. Such dynamic twinning suggests that the essential DRX nucleation mechanism is twinning.
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Authors: M. Masimov, N. Peranio, B. Springub, Franz Roters, Dierk Raabe
Abstract: Using SEM/EBSD the substructure and texture evolution in dual phase steels in the first steps of the process chain, i.e. hot rolling, cold rolling, and following annealing were characterized. In order to obtain dual phase steels with high ductility and high tensile strength an industrial process was reproduced by cold rolling of industrially hot rolled steel sheets of a thickness of 3.75 mm with ferrite and pearlite morphology down to a thickness of 1.75 mm and finally annealing at different temperatures. Such technique allows a compilation of ferrite and martensite morphology typical for dual phase steels. Due to the competition between recovery, recrystallization and phase trans-formation during annealing a variety of ferrite martensite morphologies was produced by promoting one of the mechanisms through the variation of technological parameters such as heating rate, intercritical annealing temperature, annealing time, cooling rate and the final annealing temperature. Annealing induced changes of the mechanical properties were determined by hardness measurements and are discussed on the basis of the results of the substructure investigations.
251
Authors: Stuart I. Wright, Matthew M. Nowell
Abstract: Automated Electron Backscatter Diffraction (EBSD) or Orientation Imaging Microscopy (OIM) has proven to be a viable technique for investigating microtexture in polycrystalline materials. It is particularly useful for investigating orientation relationships between phases in multiphase materials. However, when phases do not significantly vary in crystallographic structure, OIM is limited in its capability to reliably differentiate between phases. Through simultaneous collection of EBSD data and chemical data via X-Ray Energy Dispersive Spectroscopy (EDS) it is possible to dramatically improve upon the phase differentiation capabilities of either technique individually. This presentation will introduce a methodology for combining the two techniques as well as show a few example applications.
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Authors: Hiroyuki Kokawa, Masahiko Shimada, Zhan Jie Wang, Yutaka S. Sato, M. Michiuchi
Abstract: Optimum parameters in the thermomechanical treatment during grain boundary engineering (GBE) were investigated for improvement of intergranular corrosion resistance of type 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation (EPR) and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice (CSL) boundaries indicated a maximum at the small pre-strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface.
1005
Authors: Alexandre P. Zhilyaev, Keiichiro Oh-ishi, Georgy I. Raab, Terry R. McNelley
Abstract: The influence of strain path during equal-channel angular pressing (ECAP) has been evaluated in pure aluminum by orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). The material was examined after four pressing operations by route BC in a 90° die, or eight pressing operations by route BC in a 135° die. The von Mises equivalent strains were essentially the same for these two ECAP procedures. The microtexture data indicate that the distortion during ECAP corresponds to a simple shear in a direction approximately parallel to diechannel exit and on a plane perpendicular to the flow plane. For both procedures the OIM data reveal prominent meso-scale band-like features. Lattice orientations in each band correspond to a texture orientation but the particular combinations of orientations depend upon ECAP die angle. High-angle boundaries in the structure correspond to interfaces between the bands.
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Authors: Vàclav Sklenička, Petr Král, Jiří Dvořák, Marie Kvapilová, Milan Svoboda
Abstract: The creep behavior of high purity aluminum and copper, Al-0.2wt.%Sc and Cu-0.2wt.%Zr alloys was examined after processing by equal-channel angular pressing (ECAP) with an emphasis on the link between microstructure and creep. The microstructure was revealed by electron backscatter diffraction (EBSD) and analyzed by stereological methods. Representative microstructural parameters were obtained using orientation imaging microscopy and EBSD on the relationship between creep behavior and microstructure.
2689
Authors: Herbert M. Miller, Chang Soo Kim, Jason Gruber, Valerie Randle, Gregory S. Rohrer
Abstract: The distribution of grain boundary plane orientations in polycrystalline Ni has been measured before and after grain boundary engineering. The grain boundary engineered microstructure has a relatively higher concentration of Σ3 grain boundaries and, when compared to the initial structure, more of these boundaries have orientations that are inclined by more than 10° from the (111) orientation of the ideal coherent twin. Although the conventionally measured grain size is not affected by the grain boundary engineering process, the average size of the regions containing only Σ3n grain boundaries increases by nearly a factor of two. The observations indicate that the increase in the relative population of Σ3 grain boundaries results both from the preferential elimination of random grain boundaries and the generation of new Σ3 grain boundaries which do not have (111) grain boundary plane orientations.
641
Authors: Julia Ivanisenko, Alexander Minkow, Ruslan Valiev, Hans Jorg Fecht
Abstract: A comprehensive investigation of microstructure evolution upon annealing in the temperature range between 100°C and 450°C in SPD-processed nanocrystalline iron had been conducted using transmission and orientation imaging microscopy, and XRD analysis. The asprocessed microstructure was typical of severely deformed metals consisting of grains with a mean size of 110 nm, each subdivided by a network of subgrain boundaries. Additionally, measurements of microstrains using XRD found a very high microstrain level of 0.003 in this material. After annealing at 200°C a drastic decrease of microstrains was observed; whereas no notable changes in the size of grains and subgrains as well in misorientation spectra have been revealed. Thus we relate this decrease of microstrains with recovery of non-equilibrium grain boundaries. Annealing at higher temperatures hadn’t led to further decrease of microstrains, but resulted in slight subgrain growth from 65 to 78 nm accompanied by increase of mean misorientation angle from 5° to 6.3°at 450°C. This indicates the occurrence of coalescence of subgrains as additional recovery mechanism.
891
Authors: H. Paul, Thierry Baudin, K. Kudłacz, A. Morawiec
Abstract: The objective of this study was to determine the effect of deformation mode on recrystallization behavior of severely deformed material. Commercial purity AA3104 aluminum alloy was deformed via high pressure torsion and equal channel angular pressing to different strains and then annealed to obtain the state of partial recrystallization. The microstructure and the crystallographic texture were analysed using scanning and transmission electron microscopes equipped with orientation measurement facilities. The nucleation of new grains was observed in bulk recrystallized samples and during in-situ recrystallization in the transmission microscope. Irrespective of the applied deformation mode, a large non-deformable second phase particles strongly influenced strengthening of the matrix through deformation zones around them. It is known that relatively high stored energy stimulates the nucleation of new grains during the recrystalization. In most of the observed cases, the growth of recrystallized grains occurred by the coalescence of neighboring subcells. This process usually led to nearly homogeneous equiaxed grains of similar size. The diameter of grains in the vicinity of large second phase particles was only occasionally significantly larger than the average grain size. Large grains were most often observed in places far from the particles. TEM orientation mapping from highly deformed zones around particles showed that orientations of new grains were not random and only strictly defined groups of orientations were observed.
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