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Modified method of Burger’s vector identification in a B2 structure

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Some scientific studies, aimed for example at examining the mechanism of plastic deformation of iron aluminides based on the intermetallic B2 FeAl phase, require determination by means of a transmission electron microscope of the dislocation structure, i.e. the type of dislocations responsible for the deformation process at various temperatures [1÷3]. Phase identification by means of electron diffraction analysis is usually carried out using the equation: d L r hkl = λ / (1) where: Lλ - is the microscope’s constant, r - is the distance of hkl reflection from the zero reflection. Dislocations may be observed by an electron microscope using an interference contrast, diffraction contrast or moiré effect [4]. The diffraction contrast is most often used in dislocation studies, which occurrence results from a deformation field around a dislocation. Detailed analysis of phase contrast effects allows accurate description of a dislocation, hence determination of its Burger’s vector (direction, sense and length) as well as its location in the specimen, i.e. the dislocation direction, at simultaneous precise determination of the foil orientation. The contrast was discussed inter alia in papers [5÷9]. Dislocation line directions are determined by means of standard tracks analysis, while Burger’s vectors are determined based on the criterion of contrast decay b·g = 0. In Sekido work [10], the Burger’s vectors of the dislocations formed in the intermetallic Mo5SiB2 (T2) phase were determined by the weak-beam thickness fringe method and the invisibility criterion. The method of Burger’s vector identification used now is not unequivocal, because it allows making an error despite the correctness of all operations. The paper presents a modified method of Burger’s vector determination for the dislocation studied based also on the contrast decay criterion, which, however, eliminates a possibilit[...]

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