Papers by Keyword: Kossel Microdiffraction

Abstract: Kossel microdiffraction is one of a few experimental methods of investigating heterogeneities of elastic stresses within crystallites. With digitally recorded back-reflection Kossel patterns, one can determine absolute lattice parameters, and hence lattice strains and stresses, based on geometry of Kossel lines, but the strain resolution of this approach is limited by finite widths of the lines. A new method is proposed which considerably improves the resolution in cases when the patterns originate from areas with similar lattice orientations. The method is based on determination of differences between pattern geometries: lattice strains are calculated from mutual shifts of intensity profiles of Kossel lines. The strain accuracy of this profile-based approach was estimated. It is demonstrated that the limit of strain resolution reaches a few parts per hundred thousand, i.e., it is nearly one order of magnitude better than that of the conventional Kossel-based lattice parameter refinement. This improvement concerns the critical range of lattice strain, and it constitutes a qualitative leap in resolution. The paper describes main aspects of the new approach and strain resolution tests.

Abstract: The Kossel microdiffraction in a scanning electron microscope allows for local stress determination. This technique has been applied to monitor stress evolution within grains of austenite in the course of martensitic transformation in a shape memory alloy. Kossel diffraction patterns were recorded during in situ tensile straining of Cu-Al-Be alloy. These innovative measurements show large stress heterogeneities between grains, with the stress ratio exceeding two. As martensite variants are stress-induced, shear stress components appear in individual grains of austenite.

Abstract: A Kossel microdiffraction experimental set up is under development inside a Scanning Electron Microscope (SEM) in order to determine the crystallographic orientation as well as the inter- and intragranular strains and stresses. An area of about one cubic micrometer can be analysed using the microscope probe, which enables to study different kinds of elements such as a grain boundary, a crack, a microelectronic component, etc. The diffraction pattern is recorded by a high resolution Charge-Coupled Device (CCD) camera. The crystallographic orientation, the lattice parameters and the elastic strain tensor of the probed area are deduced from the pattern indexation using a homemade software. The purpose of this paper is to report some results achieved up to now to estimate the reliability of the Kossel microdiffraction technique.

Abstract: We have developed a new convenient tool for local stress and strain analysis in the scanning electron microscope. It is based on the Kossel diffraction, physical phenomenon that is known for a long time because of its high accuracy for lattice constant determination in micron regions. The pattern is recorded on a CCD camera allowing a fast and reliable analysis. This technique has been applied to several materials. In-situ tensile tests were performed on a shape memory alloy. During loading, we observe clearly a shift of Kossel lines on the diagram, whose magnitude depends on the (hkl) crystallographic planes. The stress can be deduced from the diffracting plane strain measurement using a single crystal stress analysis.