Modeling Non-Equilibrium Microstructure Formation

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该奖项支持理论和计算研究和教育，以进一步发展原子长度尺度和扩散时间尺度的相场建模方法，并实现多组分合金的模拟。通过使用“相场”建模方法，增强了对许多非平衡过程的理解。这些方法已被证明在模拟凝固现象的许多方面非常成功，现在已被纳入商业软件包。最近，PI和合作者引入了第二代相场模型，该模型描述了原子长度和扩散时间尺度上的现象。这种“相场晶体”方法除了传统的凝固和相分离模型的所有物理特性外，还自然地结合了弹性、塑性、各向异性和多晶取向。而针对单原子和二元合金开发的相场晶体模型可以描述许多物理现象，包括晶粒生长、外延生长、共晶凝固、多晶材料的屈服强度、爬升和滑移，和晶界熔化，有许多重要的现象，目前的模型无法描述。例如，二元模型不能描述多组分合金中的亚晶格有序。这是一个关键问题，因为亚晶格排序是非常常见的，影响结构特性。当前相场晶体模型的另一个限制是它们描述了球对称粒子，因此不能描述与额外自由度（例如旋转）相关的物理学。利用这些自由度的一个重要的技术例子是弹性体;细长交联聚合物的旋转允许几乎零能量成本的剪切应变。这个项目的目标是大大扩展相场晶体建模的适用性，将亚晶格有序和各向异性粒子。PI还计划将Goldenfeld及其合作者开发的单原子相位场晶体的振幅扩展到二元系统。振幅法结合了许多基本的弹性和塑性行为，更适合于分析和数值计算。由此产生的模型将被用来研究的离散性质的晶格和组成的均匀性的影响，在应变epitaxial films.The PI的形态不稳定性与威利出版合同写一本书在材料科学相场建模。大部分的文字将致力于相位场晶体配方在这个建议和过期的NSF赠款。文本将被写为工程和物理学的学生谁希望学习相场建模的基础知识和技术细节的教学指南。PI将雇用和培训尖端计算材料物理学的本科生。这项工作也将对许多研究领域产生影响，因为所开发的方法适用于广泛的现象，如多组分合金的结构特性，弹性体的奇异弹性特性和应变外延生长中量子点的形成。该奖项支持理论和计算研究和教育，以进一步开发潜在的强大计算机模拟方法由PI和合作者开发的材料。 这项研究涉及一种称为相场建模的建模技术的扩展，这种技术计算速度快，但对许多原子的长度尺度很有用。该扩展使计算机模拟能够访问更短长度尺度、原子长度尺度和更长时间的信息。材料加工和相关材料现象的模拟跨越从单个原子到微米的许多长度尺度是新方法的有前途的应用。PI还将写一本关于相场建模及其在建模材料和材料相关现象中的应用的书。本科生将参与与本项目直接相关的研究活动。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Technical SummaryThis award supports theoretical and computational research and education to further develop methods of phase field modeling to the atomic length scale and diffusive time scales and enable the simulation of multi-component alloys.The understanding of many non-equilibrium processes has been enhanced by the use of "phase-field" modeling methods. These methods have proven very successful in modeling many aspects of solidification phenomena and are now incorporated in commercially available software packages. More recently the PI and collaborators have introduced a second generation of phase field models that describe phenomena on atomic length and diffusive time scales. This "phase field crystal" method naturally incorporates elasticity, plasticity, anisotropy and multiple crystal orientations in addition to all the physics of traditional models of solidification and phase segregation.While the phase field crystal models developed for monatomic and binary alloys can describe many physical phenomena, including grain growth, epitaxial growth, eutectic solidification, the yield strength of polycrystalline materials, climb and glide, and grain boundary melting, there are many important phenomena that are beyond description by the current models. For example, the binary model cannot describe sublattice ordering in multi-component alloys. This is a key issue since sublattice ordering is extremely common and influences structural properties. Another limitation of current phase field crystal models is that they describe spherically symmetric particles and thus cannot describe the physics associated with extra degrees of freedom, such as rotation. A technologically important example which exploits these freedoms is elastomers; the rotation of elongated cross-linked polymers allows shear strains at almost zero energy cost. The goal of this project is to greatly extend the applicability of phase field crystal modeling to incorporate sublattice ordering and anisotropic particles. The PI also plans to extend the amplitude expansion of the monatomic phase field crystal developed by Goldenfeld and collaborators to binary systems. The amplitude approach incorporates much of the essential elastic and plastic behavior and is more amenable to analytic and numerical calculations. The resulting model will be used to examine the influence of the discrete nature of the crystalline lattice and compositional in homogeneities on morphological instabilities in strained epitaxial films.The PI has a contract with Wiley publishing to write a book on phase field modeling in materials science. Much of the text will be devoted to the phase field crystal formulations developed in this proposal and in the expired NSF grant. The text will be written as an instructional guide for engineering and physics students who wish to learn the fundamentals and technical details of phase field modeling. The PI will hire and train undergraduate students in cutting edge computational materials physics. The work will also have an impact on many areas of research since the methods developed are applicable to a wide range of phenomena such as the structural properties of multi-component alloys, the exotic elastic properties of elastomers and the formation of quantum dots in strained epitaxial growth.Non-Technical SummaryThis award supports theoretical and computational research and education to further develop a potentially powerful method for computer simulation of materials that was developed by the PI and collaborators. The research involves the extension of a modeling technique, called phase field modeling, that is computationally fast but useful on length scales of many atoms. The extension enables computer simulations to access information on much shorter length scales, atomic length scales, and longer times. Simulations of materials processing and related materials phenomena that span many length scales from single atoms to microns are promising applications of the new method.The PI will also write a book on phase field modeling and its application to modeling materials and materials related phenomena. Undergraduate students will be involved in research activities directly related to this project.