Method and Appartus for Forming Ultrafine Metal Powders
Seaman, Frederic D.
Altergott, William H.
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A method and apparatus for producing ultrafine metal powders in which a laser beam is focused on the surface of a workpiece or feedstock and moved thereacross so as to create a cavity within the workpiece through melting and vaporization that contains the metal melted to form the cavity. A subsonic pulsating blast of inert gas is directed at the cavity to atomize the molten metal, rapidly cool the resulting droplets, and transport the droplets to a collection area. The cavity formed by the laser beam is a "keyhole" of deep cavity having a depth approximately three to four times greater than its width. The focal point of the laser beam is moved across the workpiece at a rate from approximately 50 to 80 inches per minute to ensure that the molten metal remains in the cavity prior to the gas atomization. Alloy metal powders can be produced by this method of laser blast atomization providing an alloying metal at the base metal where the cavity is formed so that, upon melting of the base metal, the alloy metal will melt into solution with the molten base metal in the cavity prior to gas atomization. Additionally, nonmetallic impurities may be removed from the molten metal contained within the cavity formed by the laser beam by vaporization.