The physics of mechanical alloying: A first report
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I.
INTRODUCTION
M E C H A N I C A L alloying (MA) is a process used for producing powders having a fine microstructural scale and/or as a technique for alloying difficult or normally incompatible materials. Mechanical alloying has found its greatest applications in the production of precursor powders for Al-, Ni-, and Fe-base superalloys but has also been used to produce powders for nonstrnctural applications such as protective coatings and reactive metals.t~-~sl The capability of the MA process to produce powders with unique microstructures has been clearly established. The process is also inherently flexible. As such, it is reasonable to expect it to grow in importance. However, there are considerable gaps in the fundamental knowledge base relative to MA, as there has been little attempt to analyze it in a manner that would establish predictive capabilities for it. Indeed, previous work has only provided a minimal quantification of the process.* Un*Since this paper was first submitted, Davis e t al. U91have reported on experimental and modeling studies of M A , which have an intent much like this paper. We shall compare results c o m m o n to the two papers in appropriate sections,
doubtedly, this is a result, in part, of the difficulties attendant to describing such a complex process in other than a qualitative way. A quantitative description of MA would be most valuable for providing further understanding of it. Since the process is so complex, complete success in such an undertaking is probably not possible in a first effort. However, such an attempt might serve to identify critical process variables and, in so doing, delineate optimum processing paths. In short, clarification of the basic mechanics and physics of the process would remove much of the empiricism which currently characterizes production of MA powders and would provide for a better assessment of process capabilities and limitations. Modeling of the MA process is the purpose of this paper. We have done this in a simplified manner, befitting such a first effort. However, and as described in detail in later sections, our approach does define the geD.R. M A U R I C E , Graduate Student, and T.H. C O U R T N E Y , Professor and Chairman, are with the Department of Materials Science, University of Virginia, Charlottesville, VA 22901. Manuscript submitted December 9, 1988.
METALLURGICAL TRANSACTIONS A
ometry and basic mechanics of the powder-workpiece interaction for several common devices used for MA. This information allows pertinent parameters of the process (e.g., impact velocities, powder material volume impacted, times between impacts, etc.) to be identified in terms of machine characteristics and process operating parameters. We realize our description will be subject to correction and refinement as the appropriate empirical correlations are made and the analysis further developed, but we believe it is worthwhile to report on it now in order to establish appropriate directions for further work. II.
OVERVIEW OF THE PROCESS
A brief overview
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