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What are the powder metallurgy techniques for powder production?

2022-01-14

　　The powder metallurgy process inevitably involves the preparation of powders. The powder preparation techniques can be broadly categorized into three main types: one is rapid solidification atomization powder production technology; another is mechanical alloying powder production technology; and the third is ultrafine powder preparation technology.

　　The rapid solidification atomization powder production technology in powder metallurgy is relatively straightforward: it involves rapidly quenching and solidifying liquid metals or alloys after they have been broken into fine droplets, thereby producing powdered materials. This type of powder production technology can effectively reduce segregation of alloy components, resulting in alloy powders with a more uniform composition.

　　Due to the different atomization media used, there are various atomization methods available in powder metallurgy powder production technologies, such as two-fluid atomization, gas atomization, high-pressure water atomization, centrifugal atomization, and vacuum atomization. In two-fluid atomization, after the atomization medium and the molten metal stream are ejected through a nozzle, the two streams collide with each other, thereby breaking up the molten stream into fine particles and producing powdered material.

　　In gas atomization, the gas pressure typically needs to reach between 2 and 8 MPa; only under these conditions can smooth-surfaced powder particles be produced for use in powder metallurgy. In contrast, water atomization, which employs water—a medium with a higher density—as the atomizing agent, achieves a condensation rate that is several orders of magnitude faster than that of conventional gas atomization. Consequently, the resulting powder particles generally have irregular shapes.

　　Mechanical alloying is a powder-milling technique used to produce alloy powders or composite powders from elemental powders. This process is carried out in a high-energy ball mill, where prolonged grinding between powder particles and between powder particles and milling balls is required for the powders to be broken and fractured. Due to their small particle size, ultrafine powders prepared by this method in powder metallurgy exhibit markedly different physical, chemical, and mechanical properties compared to conventional powders.

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