Fundamentals of interdiffusion microstructure maps for dual-alloy systems

Abstract

Interdiffusion microstructure maps (IMMs) are drawn on isothermal phase diagrams. They predict how the interdiffusion microstructure varies in a dual alloy when one alloy composition is fixed while the other is varied across a region of the phase diagram. The microstructure is defined in terms of its layers and the velocity direction of boundaries between layers. Previous work involved maps based on experimental, calculated and simulated interdiffusion microstructures. In the current work IMMs for four model systems were obtained from phase field simulations. The IMMs in this study differ from previous work in that one contains a more complicated IMM with seven areas separated by seven lines that meet at a seven-line node and one contains a less complicated IMM with only one area. Also, it was found that the microstructures at all nodes investigated to date are similar by having the microstructure of the initial dual alloy. During interdiffusion treatments the initial interface is stationary and only the amounts of phases on either side of the interface will vary with time. A list of fundamental properties of IMMs is given that combines findings from the current and previous work. In the list are three mechanisms by which microstructures change. One of these had not been seen before. In this mechanism an inversion of the microstructure occurs as the composition crosses from one side to the other of a two-phase region. These fundamentals are the foundation on which IMMs are constructed and can be a guide for their interpretation.