A model structure for the Al₅ _<i>−x</i>Ti_3+<i>x</i> phase using high-resolution electron microscopy

Abstract

Electron diffraction patterns of AI-Ti alloys show incommensurate as well as commensurate superstructure spots depending on the nominal composition ranging from A1-37 at.% Ti to A1-44 at.% Ti. It is shown that the alloy has a heterogeneous structure constituted of island-like precipitates in the matrix of A1Ti (L1 o structure) and that the incommensurability depends upon the size of the island which decreases with A1 content in the alloy. A model structure is proposed from the optical analysis of highresolution images obtained at 200 kV: each island of the A15Ti3 core is surrounded by a third phase having an intermediate composition which is assumed to be All lTi 7. Optical simulation of the electron diffraction pattern is tried using plane masks representing the islands of various sizes.