An analytical approach was developed to investigate nucleation, recalescence and growth of Ti-48Al (at.%) alloy droplets during their flight in a gas atomization process. Evolution of microstructure of the solidified powders was quantitatively investigated using scanning electron microscopy, transmission electron microscopy and electron back-scatter diffraction. Relationships among the initial number of nuclei, liquid/solid interface velocity and cooling rate have been established. Results showed that statistical nucleation events increased exponentially with increasing droplet size, and the powder microstructures were transformed from a twinned spherical segment into a concentric liquid/solid interface geometry. Variations of initial temperature, cooling rate and solid fraction of the droplets as a function of cooling durations for the droplets with various sizes were investigated.