Papers by Keyword: Grain Boundary Plane

Abstract: In the current paper a new method is presented that determines the five macroscopic parameters of a grain boundary (GB) from electron diffraction patterns and bright field (BF) images in a transmission electron microscope. Usefulness of the method is demonstrated on a set of GBs measured in laser crystallized Si thin films. To characterize the geometry of a grain boundary, we have to determine the misorientation between the neighboring grains, and the direction of the GB-plane. The misorientation is calculated from two convergent beam electron diffraction (CBED) patterns taken on the neighboring grains, and the plane-normal can be calculated from bright field (BF) images of the GB. The thickness of the sample is also needed and it is measured from a CBED pattern taken in two-beam condition. It has been previously observed in metallic thin films, that the GBs can minimize their energy in two alternative ways in thin films: either forming a GB plane with low energy density or minimizing the area of the plane. In the last case the GB plane is almost normal to the surface of the specimen and has a general index. We found, that boundaries with exact Σ3 misorientation generally adopted low energy-density {111} boundary planes and formed coherent twins. The rest of the boundaries adopted general index planes and minimized the surface area of the boundary. The last group included boundaries with small deviation from 3 misorientation, other special high-angle boundaries with-value>3 and boundaries with general misorientation.

Abstract: The technique of electron backscatter diffraction (EBSD) is ideal for the characterisation of grain boundary networks in polycrystalline materials. In recent years the experimental methodology has evolved to meet the needs of the research community. For example, the capabilities of EBSD have been instrumental in driving forward the topic of ‘grain boundary engineering’. In this paper the current capabilities of EBSD for grain boundary characterisation will be reviewed and illustrated by examples. Topics are measurement strategies based on misorientation statistics, determination of grain boundary plane distributions and grain boundary network characteristics.

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.

Abstract: Iterative processing, involving sequential deformation and annealing, has been carried out on copper specimens with the aim of grain boundary engineering (GBE) them. The data have provided some interesting insights into the mechanisms of GBE. The results have demonstrated that development of a high proportion of Σ3s is beneficial to properties, as shown by improved strain-to-failure for the same strength. The proportion of Σ3s saturates at approximately 60% length fraction. Analysis of the data indicates that iterative processing is not always necessary for the development of beneficial properties, and it is further suggested that the condition of the starting specimen has a large influence on the subsequent microstructural development. The present, new data are also compared with previous research on copper where all five parameters of the grain boundary network population have been measured.

Abstract: Measurements of the grain boundary character distribution in MgAl2O4 (spinel) as a function of lattice misorientation and boundary plane orientation show that at all misorientations, grain boundaries are most frequently terminated on {111} planes. Boundaries with {111} orientations are observed 2.5 times more frequently than boundaries with {100} orientations. Furthermore, the most common boundary type is the twist boundary formed by a 60° rotation about the [111] axis. {111} planes also dominate the external form of spinel crystals found in natural settings, and this suggests that they are low energy and/or slow growing planes. The mechanisms that might lead to a high population of these planes during solid state crystal growth are discussed.

Abstract: The grain boundary character distribution in an Fe-1%Si steel has been measured as a function of lattice misorientation and boundary plane orientation. There is a weak texture in the space of grain boundary planes that favors the {110} orientation. At specific misorientations, the anisotropy is larger. For example, when the lattice misorientation is 60° around [111], symmetric tilt boundaries comprised of two {110} planes on either side of the interface dominate the population. The results are consistent with observations suggesting that in a range of crystalline materials, the low energy, low index surface planes are found to dominate the distribution of internal interfaces.