Electron backscatter diffraction

About: Electron backscatter diffraction is a research topic. Over the lifetime, 15184 publications have been published within this topic receiving 317847 citations. The topic is also known as: EBSD.

Epitaxial laser metal forming: analysis of microstructure formation

Abstract: Epitaxial laser metal forming (E-LMF) is presented as a new cladding technique which combines the advantage of near-net-shape manufacturing with a close control of the solidification microstructure. E-LMF is a process where metal powder is injected into a molten pool formed by controlled laser heating. Laser surface treatment has the advantage that heat input is very localised, thus leading to large temperature gradients. This is used, in unison with closely controlled solidification velocities, to stabilise the columnar dendritic growth, thereby avoiding nucleation and growth of equiaxed grains in the laser clad. It is possible with this technique to deposit a single crystal clad by epitaxial growth onto a single crystal substrate. In this paper, the microstructure obtained by E-LMF is analysed by scanning electron microscopy (SEM), optical microscopy (OM) and indexing electron backscattered diffraction (EBSD) patterns. In particular, the grain structure formation in the deposit during the process and the influence of a subsequent heat treatment on precipitation and recrystallisation is characterised.

Diffraction contrast of electron microscope images of crystal lattice defects - II. The development of a dynamical theory

Abstract: The dynamical theory of electron diffraction is developed in a form suitable for the computation of images of crystal lattice defects such as dislocations observed by transmission electron microscopy. As shown in a previous kinematical theory, the contrast arises because the waves diffracted by atoms near the defect are changed in phase as a result of the displacements of these atoms from the perfect crystal positions. The two-beam dynamical theory of diffraction in the symmetrical Laue case is derived from simple kinematical principles by methods similar to those used by Darwin in the Bragg case. Simultaneous differential equations describing the changes of incident and diffracted wave amplitudes with depth in a crystal are obtained. In a perfect crystal these equations lead to the well-known Laue solutions of the dynamical equations of electron diffraction and in a deformed crystal they reduce to the kinematical theory when the deviation from the reflecting position is large. The effects of absorption can be included phenomenologically by use of a complex atomic scattering factor (complex lattice potential). Finally it is shown that an equivalent theory may be derived directly from wave mechanics in a way which allows the effects of absorption and several diffracted beams to be included. From the formal solution of this general theory some important symmetry relations for electron microscope images of defects can be deduced.

X-ray diffraction studies of the structure of nanometer-sized crystalline materials

Abstract: Recently, nanometer-sized crystalline materials have been proposed to represent a new solid-state structure which exhibits neither long-range order (like crystals) nor short-range order (like glasses). It was the purpose of this study to test this idea by x-ray diffraction experiments. Nanometer-sized crystalline materials are polycrystals in which the size of the crystallites is a few (1--10) nanometers. Structurally, these materials consist of the following two components, the volume fraction of which is about 50% each: a crystalline component, formed by all atoms located in the lattice of the crystallites, and an interfacial component comprising the atoms situated in the interfaces. It is this interfacial component which was proposed to exhibit an atomic arrangement without short- or long-range order. In order to test this idea, the interference function of nanometer-sized crystalline iron (6-nm crystal size) was measured by x-ray diffraction. The measured interference function was compared with the interference function computed by assuming the interfacial component to be short-range ordered or to consist of randomly displaced atoms (no short- or long-range order). It was found that the experimental interference function can only be matched by the computed one if the interfacial component is assumed to have no short- or long-range order.