X-ray radioscopic visualization of the solutal convection during solidification of a Ga-30wt%In alloy

Capabilities of the X-ray attenuation contrast radioscopy were utilized to provide a real-time diagnostic technique of the melt flow during unidirectional solidification of a Ga-30wt%In alloy from the bottom which is significantly affected by solutal convection. The solidification process was visualised using a microfocus X-ray tube. The X-ray facility provided shadow radiographs at spatial resolutions of about 10 µm at frame repetition rates of 25 Hz. We used the optical flow approach to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns appearing during the X-ray image sequence. Buoyancy-driven flow patterns were found at length scales much larger than the length scales of the solidifying microstructure. A strong coupling between convection and dendritic growth became apparent via flow-induced modifications of the concentration profile in the liquid.