Thermodynamics and Kinetics of Structural Transformations in Metal and Ceramic Systems

该奖项支持在扩散和非扩散转换中形成的应变生成复杂结构的三维演化以及在塑性变形和断裂中形成的缺陷（例如位错和裂纹）的演化方面的理论和计算研究和教育。尽管这些问题有明显的多样性，但它们之间有一个深刻的共性：它们呈现了具有长程应变诱导的各向异性相互作用的多模复杂系统的自组织问题的不同方面。PI开发的相场微弹性模型将与三维计算机模拟一起用于研究复杂的微观结构，以阐明在技术重要系统中控制其演变的机制。研究热力学、晶体对称、微弹性和动力学在微观结构演变中的相对作用，以深入了解微观结构的热稳定性机制，预测微观结构和演化速率，并帮助建立最佳的加工参数，以产生具有最佳力学性能的微观结构。本课程将讨论三组与先进材料相关的科学与工程问题。第一组，与控制有序金属间化合物的几种结构变体的立方体系中相干分解的机制有关，包括研究通过从瞬态一致有序相中析出多种有序金属间化合物，形成具有非常复杂形貌的相干两相微观结构（例如，Co-Pt和其他合金中的棋盘结构）；并研究涉及两相以上的多相相干微观结构的形成。第二组问题涉及在晶体学和弹性不均匀体系中马氏体对外加应力的响应。这一组包括马氏体相变涉及位错塑性的研究。应力适应位错对马氏体晶体的形貌有显著影响；它们会导致不可逆的塑性变形，这不利于形状记忆效应。对相变夹杂中推进裂纹产生的应力诱导马氏体相变的研究也包括在这一组中。特别令人感兴趣的是马氏体的非均匀形核，随后是裂纹尖端区域的重排，以及这种重排对裂纹系统发展的影响。模拟相应的应力-应变曲线。第三组问题涉及自由表面附近的相干扩散相变和马氏体相变。这些现象的研究之所以成为可能，是因为在美国国家科学基金会的支持下，有了一种新的理论方法。将开发有效的软件，使复杂材料系统中同时发生的多个过程的逼真模拟成为可能。该代码将分发给该领域的研究人员。馆内的虚拟实验、模拟动画和电影将被收集起来，用于材料科学和工程的公共教育。这项活动也将使更多的学生参与到先进的跨学科研究中来。对本科生和研究生的教育还有更广泛的影响。该奖项支持在扩散和非扩散变形中形成的产生应变的复杂结构的演变，以及在塑性变形和断裂中形成的缺陷（例如位错和裂纹）的演变方面的理论和计算研究和教育。PI开发的相场微弹性模型将与三维计算机模拟一起用于研究复杂的微观结构，以阐明在技术重要系统中控制其演变的机制。微观组织在材料的力学性能和加工过程中起着重要的作用。研究主要集中在三个问题领域：第一是关于控制有序金属间化合物的几种结构变体的立方体系的相干分解机制；二是与马氏体在晶体学和弹性不均匀体系中对外加应力的响应有关；第三种涉及自由表面附近的相干扩散相变和马氏体相变。将开发有效的软件，使复杂材料系统中同时发生的多个过程的逼真模拟成为可能。该代码将分发给该领域的研究人员。馆内的虚拟实验、模拟动画和电影将被收集起来，用于材料科学和工程的公共教育。这项活动也将使更多的学生参与到先进的跨学科研究中来。对本科生和研究生的教育还有更广泛的影响

This award supports theoretical and computational research and education on the 3-dimensional evolution of strain-generating complex structures formed in diffusional and diffusionless transformations as well as of the evolution of defects, e.g. dislocations and cracks, formed in plastic deformation and fracture. In spite of an apparent diversity of these problems, there is a profound commonality among them: they present different aspects of the problem of self-organization of a multi-mode complex system with a long-range strain-induced anisotropic interaction. The Phase Field Microelasticity model developed by the PI together with 3-dimensional computer simulations will be used to investigate complex microstructures to elucidate the mechanisms controlling their evolution in technologically important systems. The relative role played by thermodynamics, crystallographic symmetry, microelasticity, and kinetics in microstructure evolution will be investigated to provide insight into mechanisms of thermal stability of microstructure, to predict the morphology and evolution rate, and to help establish the optimal processing parameters to yield microstructures that provide the best mechanical properties. Three groups of problems of scientific and engineering interest for advanced materials will be addressed. The first group, related to mechanisms controlling coherent decomposition in cubic systems with several structural variants of ordered intermetallics, includes investigating the formation of coherent two-phase microstructures with a very complex morphology (e.g., the chessboard microstructure in Co-Pt and other alloys) via precipitation of multi-variant ordered intermetallics from a transient congruently ordered phase, and investigating the formation of a multi-phase coherent microstructure involving more than two phases. The second group of problems involves the response of the martensite to applied stress in crystallographically and elastically inhomogeneous systems. This group includes the study of martensitic transformations involving dislocation plasticity. Stress-accommodating dislocations drastically affect the morphology of martensitic crystals; they are responsible for irreversible plastic deformation, which are detrimental to the Shape Memory Effect. The study of stress-induced martensitic transformation generated by advancing cracks in transforming inclusions is also included in this group. Of particular interest is the heterogeneous nucleation of the martensite followed by the rearrangement of its domains in the crack tip zones as well as the effect of this rearrangement on the development of the crack system. The corresponding stress-strain curve will be simulated. The third group of problems involves coherent diffusional and martensitic phase transformations near free surfaces. The study of these phenomena becomes possible because of the availability of a new theoretical approach developed with NSF support. Effective software that will enable realistic simulations of multiple processes simultaneously occurring in complex materials systems will be developed. The code will be distributed to researchers in the field. The galleries of virtual experiments, simulation animations and movies will be collected for public education in materials science and engineering. This activity will also enable more students to participate in advanced interdisciplinary research. There are additional broader impacts in the education of undergraduate and graduate students.%%%This award supports theoretical and computational research and education on the evolution of strain-generating complex structures formed in diffusional and diffusionless transformations as well as of the evolution of defects, e.g. dislocations and cracks, formed in plastic deformation and fracture. The Phase Field Microelasticity model developed by the PI together with 3-dimensional computer simulations will be used to investigate complex microstructures to elucidate the mechanisms controlling their evolution in technologically important systems. Microstructure plays an important role in determining mechanical properties of materials and in materials processing. Research focuses on three problem areas: The first is related to mechanisms controlling coherent decomposition in cubic systems with several structural variants of ordered intermetallics; The second is related to the response of martensite to applied stress in crystallographically and elastically inhomogeneous systems; The third involves coherent diffusional and martensitic phase transformations near free surfaces. Effective software that will enable realistic simulations of multiple processes simultaneously occurring in complex materials systems will be developed. The code will be distributed to researchers in the field. The galleries of virtual experiments, simulation animations and movies will be collected for public education in materials science and engineering. This activity will also enable more students to participate in advanced interdisciplinary research. There are additional broader impacts in the education of undergraduate and graduate students.***