Kinetics of Phase Transformations

相变动力学

• 批准号: 9633596
• 负责人: Karl Ludwig
• 金额: $ 29.35万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-08-01 至 2001-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9633596&HistoricalAwards=false
• 关键词: Kinetics; Phase; Transformations

9633596 Ludwig While much progress has been made in understanding equilibrium phase diagrams, transformation kinetics has been more difficult to calculate or simulate with quantitative accuracy. This is particularly true when there are complicating factors such as long-period superlattice phases and coupling between strain and ordering. By combining synchrotron-based-time-resolved x-ray scattering capabilities with recently-developed binding energy calculations and supercomputer technology significant advances can be made. State-of-the-art energy calculations in Monte-Carlo simulations are used to understand, and predict, complex ordering kinetics as observed by time- resolved x-ray diffraction. The calculations allow for local relaxation of atoms off their ideal lattice sites as well as global lattice relaxation and symmetry change. The focus is on the classic CuAu alloy, which possesses ordered and modulated phases as well as a lattice symmetry change upon ordering. Other important issues to be investigated include the presence of separate ordering spinodals for modulated and ordered phases, formation kinetics of the ordered phase from the modulated phase, and the coupling between strain and order. In addition to CuAu alloys, other systems which exhibit long-period superlattice phases will be investigated, in particular Ti-Al alloys which exhibit a devil's staircase of modulated phases. %%% Ordering kinetics in many alloys is complicated by the presence of long-range superlattice phases and/or changes in lattice constant and symmetry. Understanding the changes in such systems is a major challenge to materials scientists. ***

小行星9633596 虽然在理解平衡相图方面取得了很大进展，但相变动力学更难以定量准确地计算或模拟。 当存在复杂因素如长周期超晶格相以及应变和有序之间的耦合时，这一点尤其正确。 通过将基于同步加速器的时间分辨X射线散射能力与最近开发的结合能计算和超级计算机技术相结合，可以取得重大进展。 蒙特-卡罗模拟中的最先进的能量计算用于理解和预测通过时间分辨X射线衍射观察到的复杂有序动力学。 计算允许原子的局部弛豫离开它们的理想晶格位置以及全局晶格弛豫和对称性改变。 重点是经典的CuAu合金，它具有有序和调制的相位，以及在有序的晶格对称性变化。 其他重要的问题进行调查，包括调制和有序相，从调制相的有序相的形成动力学，以及应变和顺序之间的耦合的存在下单独的订购旋节线。 除了CuAu合金，表现出长周期的超晶格相的其他系统将被调查，特别是Ti-Al合金表现出调制相的魔鬼的楼梯。 许多合金中的有序化动力学由于长程超晶格相的存在和/或晶格常数和对称性的变化而变得复杂。 了解这些系统的变化是材料科学家面临的一个重大挑战。 ***