A Kinetic Model for Two Step Crystallization

Abstract

A simple phenomenological model for the crystallization kinetic of two step phase transformations is proposed. The treatment assumes that an amorphous or undercooled liquid material begins to transform into a transient metastable phase which starts to grow, at the same time the final phase starts to grow inside the metastable one, consuming it but without exceeding it. The starting material and the different phases are all assumed of the same chemical composition and the transformation processes are assumed interface controlled. As a result the starting material completely transforms to the final phase and no trace of the transient one will remain. The model properly take into acount the impingement of growing grains and can be applied to a number of transformations like solidification of undercooled liquid metallic alloys and divritification of glasses and amorphous solids.