Two-dimensional long period structures in Cu-Pd. A study of the mechanism of the transition from a one-dimensional LPS to a two-dimensional LPS

Abstract

Abstract The nucleation and formation mechanisms by which two-dimensional long period structures (2D-LPS) are generated from one-dimensional long period structures (1D-LPS) in Cu3Pd alloys are analysed. A series of alloys with very specific heat treatments was prepared to permit an analysis of different static steps in the transition from 1D-LPS to 2D-LPS. This analysis is based on studies by high-resolution electron microscopy and electron diffraction, which were essential to substantiate a crystallographic model for the transformation mechanism. The proposed mechanism ascribes the formation of the 2D-LPS to the propagation of parallel sets of hairpin-shaped configurations of non-conservative antiphase boundaries. Their progression in a direction perpendicular to the 1D-LPS boundaries gives rise to the 2D-LPS. Displacement vector analysis, and detailed observations of boundary geometries, support the proposed crystallographic model. The nucleation of the transformation proceeds in two ways, both related ...