Modelling Phase Ordering Kinetics in Alloys

利用基于金属合金电子结构描述的模型研究合金中有序的Chakraborty动力学。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。这种类型的建模也将弥合实验和理论结果之间的差距，这些实验和理论结果是使用动力学Ising模型及其连续版本，即依赖时间的金兹堡-朗道模型获得的。合金的微观模型有两个特点，使生长动力学的研究具有相关性和趣味性。该模型包括弹性应变与化学有序之间耦合的描述，并包括典型的金属相互作用，如尺寸效应项和由费米表面效应引起的远程相互作用。在当前的工作中，将考虑两种类型的模型。一种是嵌入原子方法的特殊版本，它能很好地描述非过渡金属合金；另一种是基于合金的直接对相关函数的模型，它可以从无序合金的相干势近似中计算出来。众所周知，后一种方法可以很好地描述过渡金属合金，特别是任何与费米表面相关的效应。动力学研究可分为三个独立的部分：(1)包含化学和位移效应的嵌入原子哈密顿量的直接蒙特卡罗模拟；(2)基于微观模型构建的Ginzburg- Landau泛函的Langevin方程模拟；(3)提供伴随结构跃迁的最简单有序模型的广义Ising模型的研究。广义Ising模型比合金具有更广泛的适用性，并且将在任何系统中提供动力学描述，其中存在结构畸变和某些有序场之间的耦合。将对金属合金的性能进行理论研究。特别是，将研究二元合金的成分如何混合在一起形成不同的相和结构。了解这些相是如何演变的将有助于预测这些合金的性能以及不同的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. ***