Abstract
A computer simulation of lattice fringe imaging of ordered Fe-Al alloys has been carried out, using the multiple beam dynamical theory of electron diffraction as formulated by Sinclair et al. for CU3AU (1). The object of the study was to determine the suitability of the lattice fringe imaging technique for studying spatial variations in long-range order parameter in singlephase ordered specimens.In the interest of simplicity, the results of simulations in which eight beams were excited in the (200) systematic row for an imperfectly B2-ordered alloy of composition Fe-25% aluminum will be presented. (The prototype crystal structure for the FeAl phase is CsCl.) Simulated images were obtained by combining the direct beam with the (100) superlattice reflection, for the case in which Bragg's Law was satisfied for the (100) reflection, and with both beams equidistant from the optic axis of the microscope.Image intensities as a function of distance parallel to [200] were computed for different specimen thicknesses and long-range order parameters.
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