DISTORTION OF THE TEMPERATURE AND SOLUTE CONCENTRATION FIELDS DUE TO THE PRESENCE OF PARTICLES AT THE SOLIDIFICATION FRONT - EFFECTS ON PARTICLE PUSHING

When the solidification front of an alloy approaches a particle in the melt, interactions take place between them due to three main reasons: (1) the molecular surface forces between the particle and the front, (2) distortion of the temperature field because of the different thermal properties of the particle and (3) distortion of the solute concentration field due to blocking of solute diffusion from the front by the particle. All the three effects result in changes of the front morphology. If the molecular surface forces are repulsive, the front can push the particles along with it unless the repulsive force is overcome by the viscous drag on the particle. The magnitude of the forces depend on the dimensions of the gap between the particle and the front and hence on the morphology of the front. In this paper the distortions in the temperature and concentration fields and the consequent changes in front morphology are evaluated, and the conditions for pushing or engulfment of particles by the solidification front are determined. Using the results from the theory for the plane solidification front, qualitative explanations are given for observed phenomena in dendritic alloy castings containing dispersoids.