The Effect of Volume Changings on the Phase Boundary Kinetics during a Solidification Process

摘要

The density of a solid metal normally differs from the density of the corresponding liquid. The volume difference between the melt and the crystal causes primarily strain and stress over the interface. Adaptation to a stable state occurs by deformation. There are three possible mechanisms of deformation: Elastic deformation, Creep and Formation of vacancies. Each mechanism is examined in terms of free energy. The calculations indicate which one of the three mechanisms that is most likely at different growth rates. It is shown that vacancies are caught in the solid at a critical growth rate. The fraction of trapped vacancies is analysed theoretically as a function of growth rate. The influence of crystallographic growth direction on the fraction of trapped vacancies, is also analysed. The effect of lattice defects on the thermodynamics of the solid and their effect on the solute distribution is investigated theoretically by aid of thermodynamic models.