Aluminum-base Amorphous Powders with Flaky Morphology Prepared by a Two-Stage Quenching Technique

Abstract

Al85Ni7.5Mm7.5 and (Al0.85Ni0.075Mm0.075)98Mg2 (Mm=mischmetal) amorphous powders were produced by the two-stage quenching technique consisting of high-pressure argon atomization followed by melt spinning. These amorphous powders have a flaky morphology with a disc or ellipsoidal shape and a thickness of about 1 to 3 μm and the powder size is above 25 μm. The unique morphology and amorphization for the Al-based powders are presumably because of the impact flattening of atomized liquid droplets which were supercooled below the melting temperature. A decrease of powder size to 5–25 μm results in crystalline powders with a spherical morphology because of a lower cooling rate resulting from solidification during single-stage gas atomization. The absence of the second-stage impact flattening for the small powders is explained by the lower value of the kinetic energies generated by the first-stage high-pressure gas atomization process. © 1989, The Japan Institute of Metals. All rights reserved.