DIRECTIONAL DENDRITIC SOLIDIFICATION OF A COMPOSITE SLURRY - PART I -DENDRITE MORPHOLOGY

A simple analytical model to describe the morphology of a growing dend rite in the presence of an inert particle has been presented. The pres ence of a particle changes the solute concentration gradient at the ti p of a growing dendrite and this, in turn, affects the dendrite tip ra dius. Results of the analysis show that the dendrite tip radius decrea ses at a high growth velocity due to the presence of a particle, while there is no influence on the tip radius at both low and intermediate growth velocities. Lower thermal conductivity of the particle decrease s the tip radius, while a higher thermal conductivity increases the ra dius. However, the effect of thermal conductivity on the tip radius is only significant in the cellular growth regime. The analysis shows th at the presence of SiC particles in Al-Cu alloys reduces the cell to d endrite transition velocity. Results of directional solidification exp eriments carried out on an Al-4.5Cu-SiC composite system agree with ou r model.