Interaction between droplet and advancing solidification interface during solidification of immiscible alloys

The liquid-liquid phase transformation during the solidification of an immiscible alloy provides a route for developing the in-situ particulate composite of high performances. Researches demonstrate that the repulsion of solidification interface to the minority phase droplet may cause the formation of a microstructure with the minority phase droplets/particles enriched on grain boundaries or even a macro-segregated microstructure. The interaction between a solidification interface and droplets has not been well considered up to now. Generally, the models for the interaction between a particle and solidification interface were used to predicate the interaction between a droplet and solidification interface. In fact, the droplet nearby solidification interface may behave much differently from a particle due to its fluidity. This work develops a model describing the interaction between an advancing solidification interface and its nearby droplets. The model is verified by comparing with the experimental results. The factors influencing the capture of droplets by solidification interface are discussed in details. The numerical results demonstrate that the Marangoni migration of droplets makes the capture of droplets harder compared with the capture of particles. With the increase of the relative viscosity of the droplet to the matrix melt, the capture the droplet becomes easy. The Marangoni migration velocity is negligible small for a droplet of very high viscosity. The capture of such a droplet by solidification interface is similar to the capture of a solid particle.