Propriétés des parois d'antiphase dans les alliages ordonnés fer˗silicium

Abstract

Antiphase boundaries formed in the course of growth and cooling of single crystals of Fe-Si alloys containing from 10 to 24 atomes % Si were studied. They were chiefly examined by transmission electron microscopy. It is shown that the contrast of boundaries with displacement vectors 1/4 a'₀ < 111 > and 1/2 a'₀ < 100 > approximately parallel to the electron beam is qualitatively different for high and low Si contents. These boundaries with vector 1/2 a'₀ < 100 > show an anomalous contrast even in superlattice reflections for which theory predicts zero contrast. In a certain concentration region the boundaries of both types have preferred crystallographic orientations (planes {100}). Some contrast of boundaries was observed even in the fundamental reflections. The contrast of boundaries parallel to the beam and anomalous contrast of boundaries with 1/2 a'₀ < 100 > vector can be explained by the existence of a disordered layer several atomic planes thick. The preferred crystallographic orien¬ tation shows that the energy of the boundaries cannot be derived from the simple model according to the Bragg-Williams theory. It is suggested that the energy is influenced by the lattice deformation which is proved by the contrast of boundaries in the fundamental reflections.