Observation of sidearm splitting studied by high resolution X-ray radiography

The local dynamics of dendritic sidearms during the growth stage are studied by in-situ radiography observations at high spatial resolution of < 1 µm. A flat sample of a Ga-In alloy is solidified top-down applying a vertical temperature gradient. The evolving dendritic microstructure is visualized using synchrotron X-ray imaging at the beamline ID19 (ESRF, France). The experimental investigations on the dendrite evolution revealed a transition from a four-fold symmetry to a hyperbranched dendritic morphology. Both, the sidearm-splitting phenomena – responsible for this morphological transition – as well as the arm growth dynamics are characterized by image processing.