Abstract
Abstract The structure of a small-angle symmetrical tilt boundary in B2-ordered Fe3Al has been investigated employing transmission electron microscopy. Two different dislocation configurations have been observed; these are discussed in terms of different models for symmetrical tilt boundaries in ordered alloys as proposed originally by Marcinkowski in 1968. The first configuration consists of an array of regularly spaced superdislocations; each superdislocation is comprised of two ordinary dislocations (b = ½a 0[111]) separated by an antiphase boundary (APB) in the (111) boundary plane. The second configuration involves a set of irregular ordinary dislocations (b = ½a 0[111] associated with at least one APB in one of the crystals. The width of the APB ribbon of a superdislocation in a tilt boundary depends on the elastic properties and the APB energy γ Using anisotropic elasticity theory and estimates for γ involving first- and second-nearest-neighbour interactions the equilibrium dislocation separation in a superdislocation is found to be considerably smaller than the experimental value. Possible reasons for this discrepancy are considered.
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