Study on the Production of Amorphous Metallic Powders by Impact Flattening of Atomized Liquid Droplets on a Rapidly Rotating Wheel

Abstract

A two-stage quenching technique consisting of impact flattening of atomized supercooled liquid droplets caused the production of flaky amorphous powders with a thickness of 1 to 3 pm and an aspect ratio of 20 to 300 in Co-, Fe- and Al-based systems. The flaky powders consist of an amorphous phase over the entire particle size range even in the alloy systems where no amorphous phase is formed in the particle size below 25 μm by high-pressure gas atomization. The improvement of the production ratio of the amorphous powders is due to the following three factors; (1) the second-stage cooling of supercooled liquid droplets, (2) the reduction of powder thickness to 1 to 3 Jim, and (3) the high thermal conductive state between rotator and powder resulting from the high-energy collision. The flaky powders also have smooth surface and edge combined with a uniform thickness, leading to good luster, high reflection ratio against light, high corrosion resistance, high mechanical strength and anisotropic magnetic properties. Furthermore, the unique morphology causes a high laminating tendnency in a resin. By utilizing these advantages, the flaky amorphous powders are expected to be used as magnetic filler and corrosion-resistant coating materials.