Observation of melt flow effects and dendritic growth during directional solidification of Ga-In alloys by X-ray radioscopy


Observation of melt flow effects and dendritic growth during directional solidification of Ga-In alloys by X-ray radioscopy

Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.

Capabilities of the X-ray attenuation contrast radioscopy were used to provide a real-time diagnostic technique for the observations of dendritic growth and the melt flow during directional solidification of a Ga-30wt%In alloy. The metal alloy was contained in the 150 µm wide gap between the two quartz glass plates of a solidification cell. The solidification process was visualised using a microfocus X-ray radioscopy setup. At typical frame repetition rates of one frame per second, the experimental assembly enables both the observation of the evolution of the dendritic network at length scales of several micrometers as well as the simultaneous observation of the melt convection at nearly millimeter length scale. The Optical Flow approach was used 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 between consecutively acquired X-ray image frames. Growth rates of single primary dendrite trunks were obtained by means of a tip tracking algorithm. Therewith, aspects of the complex interaction mechanisms between melt flow and dendritic growth have been elucidated. Experiments have been carried out to solidify the Ga-In alloy unidirectionally either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection. Dendritic fragmentation can be observed during the solidification in the reverse top-down direction.

  • Lecture (Conference)
    IEEE 2008 - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany

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Publ.-Id: 11757