Modelling Phase Ordering Kinetics in Alloys

9520923 Chakraborty合金中有序化的动力学将使用基于金属合金电子结构描述的模型进行研究。 通过预测微观结构和生长规律，这些研究将提供在理论和实验之间进行定量比较的机会。 建模的类型也将弥合实验和理论结果之间的差距使用动力学伊辛模型和它们的连续版本，时间依赖的金兹伯格-朗道模型。 合金的微观模型有两个特点，使生长动力学的研究相关和有趣的。 该模型包括弹性应变和化学序之间的耦合的描述，它们包括典型的金属相互作用，如Osize-effectO项和费米表面效应引起的长程相互作用。 在目前的工作中将考虑两种类型的模型。 一个是嵌入原子方法的一个特殊版本，它提供了一个非常好的描述非过渡金属合金，另一个是一个模型的基础上直接对相关函数的合金，可以计算从相干势近似无序合金。 后一种方法是已知的过渡金属合金，特别是任何费米表面相关的效果提供了一个很好的描述。 动力学的研究可以分为三个独立的部分：（1）嵌入原子哈密顿量的直接Monte Carlo模拟，包括化学和位移效应，（2）基于Ginzburg-朗道泛函的Langevin方程的模拟，从微观模型构建，和（3）广义Ising模型的研究，提供了最简单的模型，有序伴随着结构转变。 广义伊辛模型具有比合金更广泛的适用性，并且将在任何系统中提供动力学的描述，其中在结构畸变和一些有序场之间存在耦合。 对金属合金的性质进行理论研究。 特别是，将研究二元合金的组分如何混合在一起以形成各种相和结构。 了解这些相如何演变将有助于预测这些合金的性能以及各种加工路径如何影响这些性能。 ***

9520923 Chakraborty Kinetics of ordering in alloys will be investigated using models based on descriptions of the electronic structure of metallic alloys. By predicting microstructures and growth laws, these studies will provide the opportunity of making quantitative comparisons between theory and experiment. The type of modeling will also bridge the gap between experiments and theoretical results obtained using kinetic Ising models and their continuum version, the time-dependent Ginzburg-Landau model. The microscopic models of alloys have two features which make the study of growth kinetics relevant and interesting. The models include a description of the coupling between elastic strains and chemical order and they include typical metallic interactions such as Osize-effectO terms and long- range interactions arising from Fermi surface effects. Two types of models will be considered in the current work. One is a particular version of the embedded atom approach which provides a very good description of non-transition metal alloys, and the other is a model based on the direct pair- correlation function of alloys which can be calculated from the coherent potential approximation to disordered alloys. The latter approach is known to provide an excellent description of transition metal alloys and particularly of any fermi-surface realted effects. The study of kinetics can be divided into three separate parts: (1) direct Monte Carlo simulations of embedded atom Hamiltonians including chemical and displacement effects, (2) simulations of Langevin equations based on Ginzburg- Landau functionals constructed from microscopic models,and (3) studies of a generalized Ising model which provides the simplest model of ordering accompanied by a structural transition. The generalized Ising model has a wider range of applicability than alloys and will provide a description of kinetics in any system where there is a coupling between a structural distortion and some orderi ng field. %%% Theoretical research will be conducted on the properties of metallic alloys. In particular, studies will be made on how the components of a binary alloy mix together to form various phases and structures. Understanding how these phases evolve will contribute to predicting the properties of these alloys and how various processing paths affect these properties. ***