ATOMIZATION OF ALLOY POWDERS

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Abstract
The critical need to enhance the performance of currently available structural materials has prompted the development of a multitude of novel synthesis techniques. Among these, atomization has received considerable attention as a result of the large degree of microstructural control that is achievable with this technique. The large body of scientific literature reviewed in this article provides some examples of the successful application of a wide variety of atomization techniques for the production of metallic powders with unique combinations of physical and mechanical properties. The energy required for disintegration of the molten metal during atomization may be imparted in several ways. The most commonly used atomization techniques are (1) fluid atomization, (2) centrifugal atomization, (3) subsonic gas atomization, and (4) supersonic and other high-energy methods. Gas atomization, however, remains the most popular approach for the efficient manufacture of a wide variety of alloy compositions, as a result of the highly nonequilibrium transfer of thermal energy associated with this technique. The scientific literature reviewed in the present work also reveals that a large proportion of the research effort has been aimed at developing equations that can be utilized to predict the resultant powder characteristics from relevant processing parameters and physical properties in an effort to (1) enhance our understanding of the fundamental mechanisms governing atomization and (2) increase the effectiveness of this technique for the manufacture of alloy powders. The research work reviewed in the present article demonstrates that most of these investigations were conducted with water, wax/polyethylene mixtures, oils, and molten waxes. Only two exceptions to this general trend were uncovered: a study involving the nitrogen atomization of cast iron (J. A. Tallmadge, 1978), and the development of a correlation to predict powder sizes during gas atomization of molten metals (H. Lubanska, 1970). The lack of experimental atomization data for metals and alloys was attributed to the extreme reactivity associated with molten metals, which renders these experiments difficult to control and interpret.

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