Milling dynamics: Part I. Attritor dynamics: Results of a cinematographic study
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I.
INTRODUCTION
M E C H A N I C A L alloying (MA) is a technique for producing powders manifesting intriguing properties. Originally developed by Benjamin and co-workers Lq some 20 years ago, MA may be described as the repeated deformation, fracture, and welding of powder by a highly energetic ball charge. [2.3] Initial applications of MA focused on the production of oxide dispersion-strengthened superalloys, t4"51 now commercially available. More recently, Al-based powders having structural uses have been developed, tr'Tl Within the last decade or so, the use of MA has been extended, at least on a laboratory scale, to the production of other kinds of materials. Intermetallics, tSm inorganic nonmetallics, t~~ nonequilibrium phases and structures, I~2,13] n a n o c r y s t a ] s , D4,15] and amorphous materials t~6,17]can all be synthesized by MA. Mechanical alloying can be conducted in a variety of devices. Commercial production is carried out in large ball or rod mills (approximately 2 m in diameter) having significant capacities. As a result of the low-energy densities of these mills, production times are long, on the order of a week. Higher energy mills require less time to "alloy" but also have lesser capacities. For example, an attritor is a common laboratory device used for MA; larger sized attritors are also feasible for small-scale commercial production. Times required to "alloy" in an attritor are typically much less than they are with large commercial mills. Still higher energy mills, such as the shaker mill (exemplified by a SPEX mill) and the planetary mill, require even lesser times for process completion. Higher energy mills are the ones usually used to produce nonequilibrium manifestations (e.g., amorphous materials) of MA. Some aspects of what occurs during MA have been known qualitatively for some time. t2,31But description of the MA process is complex and multifaceted, as it involves concepts of mechanics, mechanical behavior, heat R.W. RYDIN, Graduate Student, is with the Materials Science Program, University of Delaware, Newark, DE 19716. D. MAURICE is formerly a Graduate Student, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903. T.H. COURTNEY, Professor and Chair, is with the Department of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931. Manuscript submitted July 20, 1992. METALLURGICAL TRANSACTIONS A
flow, thermodynamics, and kinetics. In spite of (perhaps because of) this, modeling of MA has been an avenue of recent interest.~18-25] Modeling approaches can be classified into two types, local and global. Local modeling describes the various effects (thermal and mechanical) and events (deformation, fracture, and welding) that transpire when powder particles are entrapped between two colliding or sliding surfaces. ~Ls-2~ Thus, local modeling is generic in the sense that parameters (relative impact velocity, angle of impact between colliding workpieces, charge ratio, etc.) affecting the various eve
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