Characterization of Motion of Dendrite Fragment by X-Ray Radiography on Earth and under Microgravity Environment

Abstract:

In the frame of ESA-MAP (Microgravity Application Promotion) project entitled XRMON (In situ X-Ray MONitoring of advanced metallurgical processes under microgravity and terrestrial conditions), a microgravity (μg) experiment in the XRMON-GF (Gradient Furnace) setup was successfully launched in 2012 on board MASER 12 sounding rocket. During this experiment, in situ and real time observations of the formation of the solidification microstructures in diffusive conditions were carried out for the first time by using X-ray radiography. In addition, two reference experiments with the same control parameters but in ground-based conditions were performed to enable us a direct comparison with the μg experiment and therefore to enlighten the effects of gravity upon microstructure formation. This communication reports on fragmentation phenomenon observed during those experiments. For 1g upward solidification, fragmentations mainly take place in the upper part of the mushy zone. After their detachments, dendrite fragments are carried away by buoyancy force in the bulk liquid where they are gradually remelted. For μg experiment and horizontal solidification, this type of fragmentation is not observed. However, a great number of fragmentations are surprisingly revealed by in situ observation in the deep part of the mushy zone, when the liquid fraction is very small. Moreover, as soon as they are detached, the dendrite fragments move toward the cold part of the mushy zone, even in the case of μg experiment. The observations suggest that sample shrinkage may be at the origin of this fragment motion.

• Periodical: Materials Science Forum (Volumes 790-791)
• Pages: 311-316
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.790-791.311
• Online since: May 2014
• Authors: Georges Salloum-Abou-Jaoude*, Henri Nguyen-Thi, Guillaume Reinhart, Ragnvald H. Mathiesen, Gerhard Zimmermann, Daniela Voss
• Keywords: Dendrites, Fluid Flow, Fragmentation, Microgravity, Solidification, X-Ray Radiography

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