Microstructure Evolution in Solids with External Constraints and Defects

具有外部约束和缺陷的固体微观结构演化

• 批准号: 0122638
• 负责人: Long-Qing Chen
• 金额: $ 27万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-11-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0122638&HistoricalAwards=false
• 关键词: Microstructure; Evolution; Solids; External; Constraints

This award supports theoretical and computational research and education to study the evolution of microsctructure in solids. The main scientific objective of this proposal is to understand the effect of external constraints on phase transformations and microstructure evolution, and the mutual interactions between phase and defect microstructures. The PI will investigate two specific problems using the phase-field approach in combination with mesoscale elasticity theory. The first problem is concerned with phase transformations and domain structure evolution in ferroelectric thin films constrained by a substrate. A phase-field model will be developed for ferroelectric domain evolution in single-crystal films. The model will include long-range elastic and electric dipole-dipole interactions, and the appropriate mechanical and electrical boundary conditions. The initial focus will be on a number of important oxides, PbTiO3, BaTiO3, PbZrxTi1-xO3, for which there have been extensive experimental measurements and theoretical thermodynamic analyses. The PI will systematically investigate the effect of substrate constraints and film thickness on transformation temperatures, volume fractions, and the size of each orientation domain. The focus will be on the temporal evolution of ferroelectric domain structures during nucleation, growth and coarsening, as well as during the domain-wall motion and polarization switching under an electric field. The effect of internal defects, both immobile and diffusive, on domain-wall mobility and ferroelectric/dielectric responses will be studied. The second problem involves the mutual interactions between phase and dislocation microstructures in advanced alloys. Based on recent advances in phase-field modeling of dislocations, a comprehensive model for the simultaneous temporal evolution of phase and dislocation microstructures will be developed, incorporating both elastic anisotropy and elastic inhomogeneity. The PI will study the local phase equilibria, solute segregation kinetics, and nucleation and growth processes around both static and moving dislocations, by varying the solute-solvent size mismatch, elastic inhomogeneity, and the relative solute diffusivity and dislocation mobility. A major effort will be devoted to modeling the influence of solute segregation and second-phase precipitates on the dynamics of both isolated and an ensemble of dislocations under applied stresses. In particular, for a given strain rate, the effect of solute concentration, solute diffusivity, precipitate size and shape, precipitate-precipitate spacing, lattice mismatch, and elastic inhomogeneity, on the critical yield stress of an alloy will be systematically studied. Financial support for two graduate students is requested. The PI will interact closely with experimentalists for validation of theoretical predictions. He also plans collaborations with other theorists to link electronic structure calculations and mesoscale phase-field simulations for modeling phase transformations and microstructure evolution.The proposed research will impact graduate education in materials, as phase-field simulations of phase transformations and microstructure evolution are being incorporated into a graduate course as part of an educational program on thermodynamics and kinetics. User-friendly software with graphical interfaces will be developed and distributed to other institutions for educational purposes. The proposed project will also result in new computational tools that can potentially be applied to industrially important materials problems as evidenced by the existing collaborations between the PI and industry.%%%This award supports theoretical and computational research and education to study the structure of materials on length scales between the atomic and the macroscopic, the microstructure, its role in phase transformations, and its evolution in the presence of external constraints and internal defects. This is a difficult fundamental problem which directly impacts materials processing. The PI will use phase field methods and focus on evolution of domains in ferroelectric materials and the mutual interactions between phase and dislocation microstructures in advanced alloys. Dislocations play an important role in diffusion processes and phase transformations of solids. Ferroelectric materials have applications in sensors and optical components***

该奖项支持理论和计算研究以及教育，以研究固体微观结构的演化。该提案的主要科学目标是了解外部约束对相变和微观结构演化的影响，以及相和缺陷微观结构之间的相互作用。 PI 将使用相场方法结合介观弹性理论来研究两个具体问题。第一个问题涉及受衬底约束的铁电薄膜中的相变和域结构演化。 将开发用于单晶薄膜中铁电域演化的相场模型。该模型将包括远程弹性和电偶极子相互作用，以及适当的机械和电气边界条件。最初的重点将是一些重要的氧化物，PbTiO3、BaTiO3、PbZrxTi1-xO3，对此进行了大量的实验测量和理论热力学分析。 PI 将系统地研究基底约束和薄膜厚度对转变温度、体积分数和每个取向域尺寸的影响。重点将放在铁电畴结构在成核、生长和粗化过程中以及在电场下的畴壁运动和极化切换过程中的时间演化。将研究内部缺陷（固定缺陷和扩散缺陷）对畴壁迁移率和铁电/介电响应的影响。第二个问题涉及先进合金中相和位错微观结构之间的相互作用。基于位错相场建模的最新进展，将开发一个结合弹性各向异性和弹性不均匀性的相和位错微观结构同时时间演化的综合模型。 PI 将通过改变溶质-溶剂尺寸失配、弹性不均匀性以及相对溶质扩散率和位错迁移率来研究静态和移动位错周围的局部相平衡、溶质偏析动力学以及成核和生长过程。主要工作将致力于模拟溶质偏析和第二相析出物对施加应力下的孤立位错和整体位错动力学的影响。特别是，对于给定的应变率，将系统地研究溶质浓度、溶质扩散率、析出物尺寸和形状、析出物-析出物间距、晶格失配和弹性不均匀性对合金临界屈服应力的影响。请求为两名研究生提供经济支持。 PI 将与实验人员密切互动，以验证理论预测。他还计划与其他理论家合作，将电子结构计算和介观相场模拟联系起来，以建模相变和微观结构演化。拟议的研究将影响材料的研究生教育，因为相变和微观结构演化的相场模拟正在被纳入其中作为热力学和动力学教育计划的一部分进入研究生课程。将开发具有图形界面的用户友好软件并将其分发给其他机构用于教育目的。拟议的项目还将产生新的计算工具，这些工具有可能应用于工业上重要的材料问题，正如 PI 和工业界之间的现有合作所证明的那样。%%%该奖项支持理论和计算研究以及研究材料结构的教育在原子和宏观之间的长度尺度上，微观结构、其在相变中的作用以及在存在外部约束和内部缺陷的情况下的演化。 这是直接影响材料加工的难题。 PI将使用相场方法，重点研究铁电材料中磁畴的演化以及先进合金中相和位错微观结构之间的相互作用。位错在固体的扩散过程和相变中起着重要作用。铁电材料在传感器和光学元件中具有应用***