Papers by Keyword: Grain Growth

Abstract: This paper gives an overview of our recent works on the effect of magnetic annealing, i.e. annealing in a magnetic field, on the evolution of texture and grain boundary microstructure in ultra-fine grained and nanocrystalline magnetic materials differently produced; rapidly solidified Fe-6.5mass%Si ribbons, electrodeposited nanocrystalline nickel, and nanocrystalline Fe78Si9B13 alloy ribbon crystallized from the amorphous state. It was found that the effect of magnetic annealing was powerful and useful for controlling grain growth resulting in the evolution of different types of texture and grain boundary microstructure, depending on the condition of magnetic annealing. In particular, the magnetic crystallization of amorphous Fe78Si9B13 alloy was found to be powerful for producing a nanocrystalline material with a sharp texture and a special grain boundary microstructure.

Abstract: While electron backscatter diffraction (EBSD) has become an established technique within materials characterization labs around the world, the technique is still relatively young and new applications are continuing to emerge. Automated EBSD or Orientation Imaging Microscopy (OIM) systems are being used in combination with other equipment within the scanning electron microscope (SEM) to perform in-situ measurements. This includes tensile stages for observing changes in local orientation during deformation and heating stages for studying orientation changes arising during recrystallization and grain growth as well as phase transformations. In addition to these temporally three-dimensional studies, spatially three-dimensional studies can be performed by in-situ serial sectioning in microscopes equipped with both electron and focused ion beams. These in-situ techniques are briefly reviewed. The review is followed by a detailed analysis of in-situ heating experiments on copper. The movement of grain boundaries during recrystallization and subsequent grain growth are tracked. The effect of orientation relationships on grain boundary mobility and nucleation are explored. No special relationship with grain boundary mobility was observed. However, twins appear to play a significant role in the nucleation process.

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: Deformation and recrystallization texture has been investigated in Oxygen free high conducting (OFHC) copper wires drawn at room temperature to true strain of 2.31, and isothermally annealed at various temperatures between 150°C and 750°C. Local orientations of the microstructures were measured by means of electron backscattered diffraction (EBSD) technique. While the drawn wire was characterized by a major<111> + minor<100> duplex fiber texture, recrystallization occurred at annealing temperatures between 250°C and 400°C and resulted into a major<100>+minor<111> recrystallization texture. At temperatures above 500°C, the <100> dominated recrystallization texture changed to the <111> dominated growth texture due to secondary recrystallization, which favored the <111> orientation at the expense of the <100> component.

Abstract: In electroformed pure Ni and Fe-Ni alloys with nanometer-sized crystallites, grain growth that takes place during annealing results in a common texture change. With regard to the macrotextures, the as-deposited textures were of fibre-type characterized by strong <100>//ND and weak <111>//ND components, and the texture development due to grain growth was defined by strong <111>//ND fibre texture with the minor <100>//ND components. It was clarified by means of the microtexture analysis that abnormal growth of the <111>//ND grains occurs in the early stages of grain growth. The possible effects of the abnormal grain growth on the texture evolution have been discussed in terms of the orientation dependence of energy density.

Abstract: In the Fe-3%Si alloys, grade Hi-B with AlN and MnS as inhibitors, the Goss grains that abnormally grow have not a size greater than the average size of the primary matrix. In such a heterogeneous microstructure, the size factor is not a required condition for the secondary recrystallization. The abnormal growth onset of the small Goss grains appears to be related to a particular behaviour of their grain boundaries and therefore to the local texture so as the distribution of the inhibitors. The presence and the evolution of textured clusters ensure to the small Goss grains a favourable neighbourhood to grow. In this study, their growth ability is compared with that of the largest grains of the matrix. The modified Monte-Carlo approach, performed in the present study, considers the local environment of each grain, so that the growth rate is dependent of its real spatial position, the matrix heterogeneity is then taken into account.

Abstract: Nonoriented electrical steels have been widely used as core materials in motors and generators. For these applications low core loss and high permeability are required. The magnetic properties of these steels depend on the grain size and crystallographic texture of the annealed final products. The problems related to grain size control have been extensively investigated, while texture control has received much less attention. The technologies used to control the grain size in nonoriented electrical steels have approached to their limits. However, there is still some possibility for improvement of the magnetic properties through texture control. In order to explore this possibility, the evolution of recrystallization texture for nonoriented electrical steels with 2% Si was systematically studied. Texture change during grain growth was additionally analyzed. The formation of recrystallization texture is explained by oriented nucleation. This is supported by the fact that the area fraction of nuclei or recrystallized grains with specific orientation to all new grains remains almost constant during the progress of recrystallization. Most nuclei have a high misorientation angle of 25~55° with the surrounding deformed matrices. During the progress of grain growth, Goss and {111}<112> components are weakened and the random texture is strengthened. The grains of the Goss and {111}<112> orientations have smaller grain size than those of random orientation.

Abstract: Monte Carlo technique was extensively used to simulate various recrystallization stages. In this study, the effect of second phase particles is studied in presence of varied populations of low and high angle grain boundaries. Results show that a significant pinning effect can be responsible for an abnormal growth when varying the population of low angle grain boundaries.