The atomization of metals and alloys results in the rapid solidification of droplets which yields a complex interplay of nucleation undercooling, recalescence and microsegregation. Characterization of the solidified microstructure has been studied using conventional optical and scanning electron microscopy (SEM). These techniques provide limited information as only a finite number of sections of the powder can be examined. X-ray tomography using synchrotron radiation with a 1 μm beam resolution was used to generate a 3D image for the entire volume of a particle and was compared to microscopic images. The tomography experiments were carried out on Al5%Cu and Al17%Cu atomized droplets of 500 μm in diameter. Microstructural features of solidification such as shrinkage, nucleation and recalescence which are apparent in the 3D images are discussed and compared with conventional characterization methods.