Combining in-situ synchrotron X-ray techniques to study the dendrite morphology in solidifying Ga–In alloys

The processes involved in the formation of different dendrite morphologies are rather complex and still far from being fully understood. To verify existing micro-structural models in situ, in high resolution, in time and space, X-ray techniques are needed. In this work, in situ synchrotron X-ray radiography and diffraction methods have been combined to study the evolution of dendritic microstructures during the solidification of Ga - In alloys. The in situ directional solidification experiments were performed at the ID19 beamline (ESRF, France) at a high spatial resolution of < 1 µm. The dendritic growth and essential dynamics of the sidearm development were quantified. Melt flow induces various effects on the dendrite and grain morphology primarily caused by the convective transport of the solute. Usually, the morphologies of these dendrites differ from those developing under purely diffusive condition. Our observations show a facilitation of the growth of primary trunks or lateral branches, a suppression of side branching, dendrite remelting and fragmentation. The dendrite morphologies with their random character are difficult to analyse by means of the 2D radiographic projections. The flow-induced variations of the local solute concentration may result in the changes of dendrite crystal orientations. The coupling of in situ X-ray imaging with X-ray diffraction provides additionally information of the crystallographic orientation of the growing dendrites. These measurements show that the Indium dendrites grow along the orientation, typically observed in body-centered metals. The analysis of the diffraction patterns with its complex morphology show that further improvements towards a 3D imaging experiment are needed. These first results demonstrate that the combination of different X-ray techniques can provide new data about the solidification process and help to validate different solidification models.