Fe<SUB>3</SUB>Al規則格子合金におけるドメイン構造の観察

Abstract

A sequence of structural changes and the antiphase boundary (APB) contrast associated with order-disorder transitions in Fe3Al alloy were investigated by means of transmission electron microscopy, and the results are discussed in combination with those of our previous X-ray diffraction study. In the transitions B2→DO3 and α+B2→DO3, the ordering was observed to take place by nucleation and growth of the DO3 domains in the B2 and α+B2 matrix, respectively. In the latter transition the difference in size of the DO3 domains which have nucleated in the α and B2 matrices suggests that the ordering from B2 to DO3 phase is easier than that from α to DO3. In the transition B2→α+DO3, the DO3 domains nucleate at the early stage, and in their growing process the α phase precipitates in both the B2 and DO3 type APB’s. The 111 dark field image shows that the B2 type APB’s with phase angle ±π⁄2 do not produce such a clear contrast as is exhibited by the DO3 type APB’s with phase angle ±π, and the fact is qualitatively explained by the two-beam dynamical theory.