Quantitative Study of Nonequilibrium Phase Formation by Mechanical Attrition

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9902435AtzmonThis is an experimental and modeling research program on nonequilibrium phase formation and stability in ball-milled metal powders. Recent experiments demonstrate the complex behavior that results from a coupling between the evolution of phases and effects of mechanical behavior. In order to gain greater understanding of this subject the influence of sample hardness and milling parameters on the effective thermodynamics of metastable alloys is investigated quantitatively. The main alloy selected for this study is nickel-silver. Characterization methods include x-ray diffraction, calorimetry, nanoindentation hardness measurements, and transmission electron microscopy. Nanoscale composition variations are investigated by a combination of analytical and high-resolution electron microscopy, taking advantage of state-of-the-art facilities. The experimental results are compared with predictions based on (1) models of effective thermodynamics and diffusion enhancement by plastic strain, and (2) quantitative data on grain size evolution during ball milling of elemental iron. %%%This research contributes to basic knowledge in the broad field of externally forced systems, overlapping with materials science, physics, chemistry and other disciplines. Significant progress is anticipated in understanding the atomistic aspects of phase formation by ball milling. Although the complexity of the ball milling process makes this fundamental study difficult, the knowledge derived on phase and microstructure design should result in significant practical benefit.***