Analysis of in situ rapid solidification of submicron Al-Ge eutectic powders using transmission electron microscopy

Submicron powders of Al-30.3 at. pct Ge (eutectic), produced by electrohydrodynamic atomization, have been analyzed in a transmission electron microscope operating at 120 kV. Amorphous and complex crystalline structures were observed in the as-atomized condition. By using the electron beam as a local heating source, powders could be either annealed at temperatures below their melting point or melted. Molten powders were quenched at various cooling rates by altering the rate of beam obstruction. Using this technique, nonequilibrium structures were produced including metastable phases and mixed amorphous/crystalline microstructures. These various structures have been related to cooling rates and compared to the as-atomized structures. Crystallization of the amorphous regions produced by this technique has also been studied