Statistical Mechanics of Microstructural Evolution

9633346本研究旨在为两相合金的微观结构演变奠定坚实的实验基础并加深对其的理解。重点是整合和检验描述微观组织粗化动力学的几种理论。具体地说，基于点源和汇的分布来表示稀释微结构中的扩散相互作用的“快照”计算被扩展到更高的体积分数。对二元合金进行了动力学研究，发现超致密微结构中的时间指数奇怪地从经典的Ostwald熟化值1/3下降到1/4。这归因于粒子形状调节和强空间相关性的影响，这是一种尚未解释的动力学行为。总之，这项研究集中于理论和实验两方面的努力，整合和验证粗化理论的基本要素，以实现对体积分数0-1范围内微观组织演变的更统一的动力学描述。%这项资助的核心课题包括确定在整个成分范围内加工的合金的动力学规律，并用基本动力学原理解释它们。金属合金的性能取决于其微观组织，而微观组织行为主要取决于时间、温度和成分。温度控制着原子扩散的速度，而在固定温度下，平均化学成分决定了分散相的体积分数，并间接地建立了扩散和界面过程的微观结构长度尺度。***

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. ***