![]() In back reflection Laue, a beam of “white” (i.e., broad spectrum) X-rays is incident on a stationary single crystal. The Laue method can be split into two categories: back reflection and transmission. This pattern of diffracted X-rays can then be captured, typically on a photographic film, creating a unique “fingerprint” that reveals the crystal’s structure. When X-rays interact with a crystal, they are diffracted in various directions based on these factors. The principle behind the Laue method is Bragg’s Law, which establishes a relationship between the X-ray wavelength, the angle of incidence (θ), and the distance between crystal planes (d). The Laue diffraction method uses constructive interference from atomic planes within crystalline lattices during X-ray scattering to investigate the internal structures of crystals. Since 1912 when Max von Laue utilized it for the first time, the Laue method has been used to determine crystalline material structures and orientations with great success through X-ray diffraction techniques. Back Reflection Versus Transmission Laue.BKDPs included in the paper are zincblende (ZnS), silicon, germanium, GaAs, chalcopyrite (CuFeS2), TaTe4 and Er2Ge2O7. Anomalous effects in BKDPs are analyzed in detail and ways of identifying anomalous contrast in practice are discussed. Examples of the use of theoretical contrast in pattern interpretation are provided. Some important characteristics of diffraction contrast in BKDPs are analyzed with respect to the geometry of the technique, the dynamical theory of electron diffraction and crystallographic applications. Essential crystallography is discussed and methods of analysis of BKDPs to extract crystallographic information are analyzed in detail. The geometrical configurations of BKDPs are reviewed in detail and the relationship between BKDPs and the technique of electron channelling patterns (ECPs) is explored briefly. Orientation microscopy is discussed but not reviewed. The paper focuses mainly on the crystallographic applications of the technique, including discussions on point group and space group determination and strain analysis. The technique of electron backscatter Kikuchi diffraction patterns (BKDPs) in the scanning electron microscope is reviewed. Diffraction experiments point towards a phase transformation which might be responsible for the pseudoelastic behavior in Fe3Al. Closer inspection revealed the appearance of new peaks and satellite reflections on loading, which disappeared upon unloading. These large changes in the diffraction pattern point towards major structural changes inside the crystal and cannot be explained by elastic effects alone. ![]() These changes are closely correlated to the load-unload stress-strain curve. All changes in the diffraction pattern revert back close to the original pattern upon unloading. Intensities and position of various peaks changed reversibly by large amounts during the load-unload cycle. In-situ Neutron Diffraction experiments in both tension and compression show large reversible changes in the diffraction pattern upon loading. Between these two extremes, the reverse stress (stress during strain recovery) follows the Clausius-Clayperon type relationship with temperature but the forward stress remains unchanged. At high temperatures (˜393 K) pseudoelasticity is lost and plasticity commences. At very low temperatures (˜100 K) shape memory effect is seen for small amounts (˜3% in compression) of applied strain. The tensile stress-strain curve shows notable changes with varying temperature. In-situ observations on the surface revealed reversible features indicating activity on the (211) planes. No strain hardening occurred under tension even at high applied strains as opposed to compression, where the alloy strain hardened continuously. Pseudoelastic behavior was seen in both tension and compression with a distinct tension-compression asymmetry. Single crystalline, D03 ordered Fe3 Al is known to show pseudoelastic behavior at room temperature. Mechanical behavior and diffraction studies on the pseudoelastic aspect of Fe3Al have been presented in this work. It also shows interesting mechanical phenomenon like yield stress anomaly and pseudoelasticity. ![]() Fe3Al is an intermetallic compound which has shown some excellent engineering properties and has been widely studied for this reason. ![]()
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