Metal powders are produced by disrupting a molten metal stream with a high-pressure water or gas jets. The relative volumes of the metal stream and the impinging fluid together with the pressure of the atomising medium, amongst other variables, are critical in determining the particle size distribution of the atomised powder.
Finer powders, of say 20 μm diameter, are produced by using higher gas or water pressures. These are more expensive, due to the lower yields, the large volumes of gas used (usually argon) and the cost of the high pressure pumping equipment.
Water atomised particles are usually irregular in shape, whereas gas atomised particles tend to be spherical.
Metallic alloys can also be atomised to give particles, each of which has the mean composition of the original melt.
Recent developments in the powder production process lead to rapid particle cooling rates, which lead to the retention in solid solution, of phases or elements that would normally precipitate within the structure of the particle as it cools. These metastable levels can vary significantly from the equilibrium concentrations that occur during normal cooling. When the powders are consolidated and heat-treated, very high strength materials may be obtained.