Modeling of mechanical alloying: Part III. Applications of computational programs
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I.
INTRODUCTION
IN the first two parts of this series, tl,2] we established a protocol for specifying the occurrences of deformation, coalescence, and fragmentation events endemic to mechanical alloying (MA) and mechanical milling (MM), and we outlined development of a computational algorithm which simulates the temporal evolution of powder during these processes. In this, the final installment of the series, we examine the capabilities of our model by comparing predictions of it to published studies. The predictions use "first guess" data with regard to input of material properties and process variables. While we find the resulting predictions are not as accurate as they might be (typically, they are within a factor of 2 or so with respect to experimentally observed processing times, particle sizes, etc.), they do indicate the usefulness of the model documented in this seties. We also investigate the effect that uncertainties in powder property data have on model predictions. This is important for, among other reasons, property data are usually derived from bulk material and not from the powder being used during MA and MM.
II.
Fig. 1--The five stages of powder evolution during MA.Pl Particle flattening (the first stage) results from plastic deformation. This is followed by a welding dominance stage during which the average particle size increases. During the third stage (equiaxed particle formation), welding and fracturing are rather much in balance and phase lamellae within individual particles are more-or-less parallel. Random welding orientation is the fourth stage. Fracture and welding tendencies are still in balance, but a number of lamellar colonies exist within each particle. Steady-state processing, during which microstructural refinement continues, constitutes the final stage.
APPLICATIONS
A. Mechanical Alloying of Iron-Chromium in a SPEX Mill
Benjamin and Volint3] observed five stages of powder evolution during MA of two-phase Fe-Cr alloys in a SPEX (SPEX Industries, Edison, NJ) mill (Figure 1). The first-particle flattening--results from plastic deformation. Particle welding, with the average particle size increasing, follows. A subsequent stage is referred to as "equiaxed particle formation;" welding and fracture events take place
D. MAURICE, formerly Graduate Student, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903, is NRC Research Associate, Albany Research Center, U.S. Bureau of Mines, Albany, OR 97321. T.H. COURTNEY, formerly Professor, Department of Materials Science and Engineering, University of Virginia, is Professor and Chair, Department of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931. Manuscript submitted June 17, 1994. METALLURGICALAND MATERIALSTRANSACTIONSA
at approximately the same rate during this stage, and phase lamellae within individual particles remain more or less parallel to each other. The fourth stage is called random welding orientation; fracture and welding frequencies
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