Mechanism of Anomalous Grain Formation During Controlled Diffusion Solidification

Controlled diffusion solidification (CDS) is a promising casting process. It depends on mixing two precursor alloys that have different masses and temperatures. After the mixing, anomalous grains with many morphologies form in the CDS microstructure. The formation, solidification, and stability of the anomalous grains are investigated in the present study. The high impingement velocity between the liquid stream of an alloy (Alloy1) and the alloy mixture occurs during the mixing, breaking the liquid stream to form pockets of Alloy1; these pockets move in an undercooled medium, resulting in nucleation from Alloy1 that has a higher liquidus temperature. The ANSYS software was used to provide a better understanding of the formation of the liquid pockets during the mixing step. The growth starts with a high growth rate and stable solid–liquid interface, unlike the equiaxed grains that form in the conventional casting process. A two-dimensional axisymmetric model solved by COMSOL software was built to provide a better understanding of the re-distribution of the temperature and the solute in the model to study the solidification and the stability of the anomalous morphologies. The numerical results were validated with experimental observations and scanning electron microscopy.