Interaction of SiC particles with moving solid–liquid interface during directional solidification of silicon

• Investigation of interaction of solid particles with moving solid–liquid interface
• Experiments with silicon on ground and under microgravity were carried out.
• Experimental results were compared to simplified theoretical models.
• Lower critical growth velocity for particle engulfment observed under microgravity.
• Lift force due to melt flow might explain the experimental findings.

In this work, the interaction of SiC particles, having sizes of 7 µm to 300 µm, with the moving solid–liquid interface during directional solidification of silicon was experimentally and theoretically investigated. This included both convective and nearly diffusive conditions. In the nearly diffusive regime under microgravity, the particles were incorporated at a lower growth velocity than in the convective regime under 1g conditions. The experimental data were compared to simple theoretical models allowing the calculation of the critical growth velocity for the incorporation of spherical particles in dependence of the particle size. It was found that the theoretical results could qualitatively explain the experimental observations when a proper set of equations for the forces acting on the particle and of the material constants are chosen. It can be concluded that sedimentation of the particles due to gravity seems to play a role only for large particles. On the other hand, melt flow might cause a lift force which would push the particles away from the solid–liquid interface, and thus would result in higher critical growth velocities under convective conditions, e.g. due to buoyancy convection. Therefore, a contribution of the missing lift force under µg conditions could lead to the smaller critical growth velocity for particle incorporation that is observed under microgravity.