Visualisation of the concentration distribution and the flow field in solidifying metallic melts by means of X-ray radioscopy

Capabilities of the X-ray attenuation contrast radioscopy will be demonstrated to provide a real-time diagnostic technique of the melt flow during solidification of Ga-In alloys. Directional solidification processes of binary metallic Ga-In alloys were 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. The optical flow approach has been adapted to determine the velocity of the liquid, the mass transport and the dendritic growth rate in the mushy zone from translocations of concentration contour lines appearing during the image sequence. Buoyancy-driven flow patterns were found ahead of the solidification front at length scales much larger than the dendrite spacing.