Observation Of Side Arm Splitting Studied By High Resolution X-Ray Radiography

The local dynamics of dendritic side arms during the growth stage were studied by in-situ radiography observations at high spatial resolution of better than 1 mu m. A flat sample of a Ga-In alloy was solidified top-down applying a vertical temperature gradient. The evolving dendritic microstructure was 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 side arm-splitting phenomenon - responsible for this morphological transition - as well as the arm growth dynamics were characterized using image processing.