Papers by Keyword: Orientation Image Microscopy (OIM)

Abstract: In situ orientation mapping using TEM and calorimetric measurements were carried out to investigate the annealing behavior of cold-rolled 6013 aluminum alloy. The recrystallization of the material can be considered to be a number of processes that correspond to two separate stored energy release peaks. In the temperature range of the peak 1, the deformation zones around the large second-phase particles acted as sites for particle-stimulated nucleation. In the matrix, at the same time, some elongation of grains occurred. The elongated matrix grains appeared because of the reduction of the dislocation density and the annihilation of some low-angle grain boundaries between chains of subgrains lying in layers parallel to the sheet plane. The matrix processes in this temperatures range can be considered forms of continuous recrystallization. The matrix high-angle grain boundaries started to migrate at the temperature range of the peak 2. They moved mostly in the direction normal to the sheet plane. Heating of the sample for an appropriate time at those temperatures resulted in the complete discontinuous recrystallization of the material. The recrystallized microstructure was dominated now by elongated grains, which were a few times thicker than those obtained by annealing at the temperatures of the peak 1.

Abstract: Experiments were conducted on extremely coarse-grained pure copper to evaluate the effect of equal-channel angular pressing (ECAP) on microstructure evolution in the as-pressed state and after creep exposure using various stereological methods. The microstructure formed by severe plastic deformation is an unusual structure which can be hardly characterized only by the mean grain size especially after low number of ECAP passes. The purpose of this paper is a detailed examination of (sub)boundaries and grain boundaries in the microstructures of the pressed material. The inhomogeneity of deformed microstructures is also evaluated. The detailed description of ECAP microstructures should contribute to the better understanding of mechanical properties of the pressed materials.

Abstract: Orientation mapping in transmission electron microscope was successfully applied to study microstructural changes at the initial stage of recrystallization in the aluminum alloy with a bimodal second-phase particle distribution. The alloy samples were reversibly cold rolled resulting in the formation of laminar structure with zones of localized strain around large second-phase particles. Orientation mapping and in-situ investigations carry information about the processes which are active in the deformation zones during annealing.

Abstract: The texture evolution due to grain growth that takes place during annealing was investigated in nanocrystalline Fe-Ni alloys fabricated by using an electroforming method. In the current materials, the as-deposited textures were of fibre-type characterized by strong <100>//ND and weak <111>//ND components, and the occurrence of grain growth during annealing resulted in the strong development of the <111>//ND components with a significant decrease of the <100>//ND components. It was clarified that abnormal grain growth plays an important role on the evolution of the microstructures and textures. The abnormally grown grains were observed using orientation imaging microscopy in the early stages of grain growth, and their morphological features have been discussed.

Abstract: The effect of ECAP technology on the subgrain structure of coarse-grained pure aluminium is described by means of the orientation imaging microscopy (the selected lower bounds of misorientation (disclination) are
= 2o, 5o, 10o and 15o). Standard profile and intercept counts carried out in three suitably oriented and mutually perpendicular section planes and along 18 systematically oriented directions, resp., are used to examine the subgrain and grain structures after the number of passes N = 2, 4, 8, 12 as well the effect of subsequent annealing (several hours at 473K). The local and overall non-homogeneity and anisotropy of boundary structures have also been evaluated.

Abstract: The microstructural evolution and the softening behavior of hot rolled and 60% cold rolled 0.85wt% carbon pearlitic steels during spheroidization annealing have been investigated by using the textural and microstructural information contained in the Orientation Imaging Microscopy (OIM) scans. The local boundary energy map, recently suggested by the present authors, is used to monitor the changes of stored plastic strain energy distribution in ferrite during the annealing process, which shows that the spheroidization process of cementite is finished before the completion of recrystallization of the 60% cold-rolled high carbon pearlitic steel.

Abstract: Mono-sized silicon particles were effectively fabricated by a novel way named pulsated orifice ejection method (POEM). The particles are with very narrow particles size distribution and very small standard deviation of mean particle size. There are two different types spherical silicon particles were found. One consists of many grains mainly in random boundaries. The other consists of two or three grains with only twin orientation relationships, even single crystal in cross-section was also found within this type spherical silicon particles.

Abstract: Specimens of commercial purity aluminum were subjected to a strain path change test during high temperature deformation. Specimens were deformed at 4000 C and strain rate of 0.1 s-1 up to various strains of 0.2, 0.5, and 1. Then in a strain path change test, specimens were first deformed to a strain of 0.5, and subsequently deformed to strains of 0.2 and 0. In order to further the understanding of the deformation mechanisms in aluminum, the subgrain sizes and misorientations were characterized in detail by comparative studies using optical microscopy in polarized light (POM), orientation imaging microscopy (OIM/SEM) and transmission electron microscopy (TEM). The analysis revealed that while subgrain size is relatively insensitive to strain, overall misorientations increased with increasing strain. These analyses confirmed a strong bimodal distribution of boundaries during deformation coupled with a low fraction of medium angle boundaries. The results contribute to the understanding that dynamic recovery in aluminum maintains subboundaries with low misorientation but as grains elongate and more subgrain become adjacent to grain boundaries the fraction of high angle boundaries rises.

Abstract: The present work is an attempt to understand the recrystallisation mechanisms in Fe-3% Si alloys used in transformer cores. After secondary recrystallisation silicon steels exhibit a Goss texture with a more or less important spread depending on the details of the processing route, namely, Conventional Grain Orientation CGO or High Permeability Hi-B. The mechanisms of Goss grain formation during hot rolling and primary recrystallisation, as well as those controlling the first steps of abnormal growth, are not yet well understood. The present work mainly deals with texture characterization of the hot rolled state. Surface, quarter and half thickness samples are prepared from hot-rolled sheet. Global and local textures are characterized by neutron diffraction and electron backscattered diffraction, respectively. The Orientation Distribution Functions and the volume fraction of the different texture components are calculated. The components from global texture measurements are (001)[1-10], (112)[1-10] (α fiber ), (011)[100] (Goss) and (111)[1-21] (111) [1-10](γ fiber). EBSD measurements have shown large variations of texture from the surface to the half thickness of the sheet. These local measurements are related to the global results by rotation about the transverse direction. Moreover, the grain size appears to be inhomogeneous.

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.