Evolution of elongated pores at the melt–solid interface during controlled directional solidification

The evolution of elongated gaseous pores during directional solidification has been examined through a theoretical model and compared to previous experimental findings from the literature. The model is based on the observation and interpretation of a wedge-shaped structure on the solid side that extends beyond the melt–solid interface and wraps around the bubble at its equator. At the tip of the wedge is the meeting point of the melt, solid and gas. The model takes into account the competition around the meeting point between the law of segregation of the solute at the melt–solid interface on one hand, and Henry’s law, which governs the concentration of the solute at the melt–pore interface at a given pressure, on the other. It predicts VR2 = constant, where V is the processing speed and R is the pore radius, and agrees well with reported experimental data.