General Methods of Metal Powder Production

Metal powders are produced by mechanical methods or chemical methods. The commonly used methods include water and gas atomization, milling, mechanical alloying, electrolysis, and chemical methods including reduction of oxides.

Suitable methods for powder production depend on required production rates, powder properties, and the physical and chemical properties of the material. Chemical and electrolytic methods are useful for producing high-purity powders. Mechanical comminution (or milling) is the most widely used method of powder production for hard metals and oxides. Secondary milling of oxide-reduced, atomized, or electrolytic powders is also a very common and economical practice. Nonetheless, mechanical comminution can be a limited method of metal powder production due to the ductility of most metals (although hydriding is a technique that can enhance powder production by milling for some metals, see the article "Milling of Ductile and Brittle Materials" in this Section).

Atomization is perhaps the most versatile method that produces metal powders over a wide range of production rates (from 1 to 105 tons/yr) and a wide variety of powder sizes from 10 to 1000 tm (Ref 1). Typical particle sizes for atomized metal powders are summarized in Fig. 1, and more detailed coverage on the basic principles of atomization are detailed in the next article in this Section. Nonetheless, a growing number of P/M applications (Fig. 2) require submicron powder sizes that are produced by chemical or physical means. Ultrafine (i.e., submicron) powders cannot be effectively produced by grinding or conventional (gas and/or liquid) atomization. Some basic physical and chemical methods of ultrafine powder production are discussed in the article "Ultrafine and Nanophase Powders" in this Volume.

Fig. 1 Approximate ranges of useful particles size and world production of different melt-atomized alloys. Source: Ref 1

Fig. 2 Some ranges of useful particle size for different applications of metal powders. Source: Ref 2

Another article also discusses powder blending and mixing techniques, including the recently developed binder-treatment blending used for metal powders. Binder-treated premixes (Fig. 3) lead to reduced dusting and segregation of alloy additions and enhanced powder flow and die filling. This results in improvements in density uniformity, weight variation, alloy homogeneity, and dimensional control of P/M parts.

Fig. 3 Alloy distribution. (a) Regular premix. (b) Segregation-free premix with powder binder and bleeding
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