Statistical Mechanics of Microstructural Evolution

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9633346 Glicksman This study is directed toward developing a firm experimental basis and deeper understanding of microstructural evolution in two-phase alloys. The focus is to integrate and test several theories that describe microstructural coarsening kinetics. Specifically, "snap-shot" calculations, based on distributions of point sources and sinks to represent diffusional interactions in dilute microstructures, are extended to higher volume fractions. Kinetic studies on binary alloys are pursued which are found to exhibit temporal exponents in ultra-dense microstructures that, curiously, decrease from the classical Ostwald ripening value of 1/3 to a value of 1/4. This is attributed to an as yet unexplained kinetic behavior from the influence of particle shape accommodation and strong spatial correlations. In summary, the research focuses both theoretical and experimental efforts on integrating and validating fundamental elements of coarsening theory to achieve progress toward a more unified kinetic description of microstructure evolution over the volume fraction range 0- 1. %%% The core subjects of this grant include determining kinetic laws for alloys processed over the full range of compositions and explaining them through basic kinetic principles. Properties of metal alloys depend on their microstructure, and the microstructural behavior depends primarily on time, temperature, and composition. Temperature controls the rate of atom diffusion, whereas, at a fixed temperature, the average chemical composition determines the volume fraction of dispersed phases, and, indirectly, establishes the microstructural length scales for diffusion and interfacial processes. ***