Ab Initio Approaches to Martensitic Transformations in Metallic Alloys

该奖项支持理论和计算研究，重点是开发和使用第一性原理方法来计算各种马氏体相变竞争机制的自由能。这些无扩散位移变换发生在各种各样的金属、半导体和陶瓷中，在材料科学中起着特殊的作用。它们构成了钢的基本强化机制，是形状记忆合金中形状记忆效应和超弹性的直接原因。PI将开发和实施基于密度泛函理论的有效从头算方法，该方法将允许精确计算电子、振动和磁熵对各种马氏体转变路径自由能的贡献。具体来说，主要目标是：(1)计算亚稳相和实验不稳定相的自由能和熵，这将为多组分合金的相图计算提供有价值的数据库；(2)计算铁中高温马氏体相变路径的热力学，同时包括振动和自旋无序熵；(3)建立了计算高温形状记忆合金中常见马氏体转变路径的自由能势垒和第一原理导出的landau型自由能泛函的有效方法；(4)建立了处理马氏体转变热力学中成分效应的新方法。本课题的成功完成将有助于更好地理解马氏体相变的热力学驱动力和微观组织机制，从而为合理设计新型高温形状记忆合金体系提供基础依据。该奖项还支持研究生的教育和向本科生介绍现代计算方法。PI将与加州纳米系统研究所和X中心合作，利用他们正在进行的努力，增加少数民族学生和未被充分代表的群体成员在工程、科学和技术领域的参与。该研究还将通过开发高通量分子动力学模拟来帮助改进计算科学教学辅助工具，这是一个旨在简化执行分子动力学模拟过程的软件平台。将要开发的软件将通过PI的集团网站免费发布。该奖项支持理论和计算研究，这些研究的重点是开发和使用无参数方法来阐明在某些类型的固体中发生的一类特殊转换的基本机制，称为“马氏体”。在马氏体相变中，排列在特定初始顺序的原子相对于它们的原子间距离扩散相对较少，以合作和均匀的运动，导致具有不同形状或对称的新原子排列。这些转变在科学上和技术上都很重要，因为它们构成了钢的基本强化机制，并且它们直接负责形状记忆效应，其中变形的合金“记住”其原始的冷锻形状，并在加热时恢复到它。PI将开发和实施有效的计算方法，以计算稳定马氏体转变路径上原子排列的各种贡献。本课题的成功完成将有助于更好地理解马氏体相变的热力学驱动力和原子机制，从而为新型高温形状记忆合金体系的合理设计提供基础依据。该奖项的教育部分包括研究生的教育和向本科生介绍现代计算方法。PI将与加州纳米系统研究所和X中心合作，利用他们正在进行的努力，增加少数民族学生和未被充分代表的群体成员在工程、科学和技术领域的参与。该研究还将通过开发高通量分子动力学模拟来帮助改进计算科学教学辅助工具，这是一个旨在简化原子或分子相互作用的物理运动的计算机模拟过程的软件平台。将要开发的软件将通过PI的集团网站免费发布。

TECHNICAL SUMMARYThis award supports theoretical and computational research that is focused on developing and using first principles methods to compute free energies for various competing mechanisms of martensitic transformations. These diffusionless displacive transformations which occur in a wide variety of metals, semiconductors, and ceramics, play a special role in materials science. They constitute the fundamental strengthening mechanism of steels and are directly responsible for the shape memory effect and superelasticity in shape memory alloys. The PI will develop and implement efficient ab initio methods based on density functional theory that will allow for accurate calculations of electronic, vibrational, and magnetic entropy contributions to the free energies of various martensitic transformation paths. Specifically, the main objectives are:(1) Calculation of free energies and entropies of metastable and experimentally unstable phases, which will provide a valuable database for phase diagram calculations of multi-component alloys, (2) Calculation of thermodynamics of high-temperature martensitic transformation paths in iron, which will simultaneously include vibrational and spin disorder entropies, (3) Development of efficient methods for calculating free energy barriers and first-principles derived Landau-type free energy functionals for common martensitic transformation paths in high-temperature shape memory alloys, and (4) Development of new methods for treating composition effects on thermodynamics of martensitic transformations.Successful completion of the proposed research program will lead to better understanding of the thermodynamic driving forces and microstructural mechanisms of martensitic transformations, hence providing fundamental basis for rational design of new high-temperature shape memory alloy systems.This award also supports the education of graduate students and the introduction of undergraduate students to modern computational methods. The PI will partner with the California NanoSystems Institute and the Center X to leverage their ongoing efforts to increase participation of minority students and members of underrepresented groups in engineering, science, and technology. The research will also aid in the improvement of computational science instruction aids via the development of high-throughput molecular dynamics simulations, which is a software platform that aims to streamline the process of performing molecular dynamics simulations. The software to be developed will be disseminated freely through the PI's group website.NON-TECHNICAL SUMMARY This award supports theoretical and computational research that is focused on developing and using parameter-free methods for elucidating the fundamental mechanisms of a special class of transformations, called "martensitic", that occur in some types of solids. In martensitic transformations, atoms arranged in a particular initial order diffuse by relatively small amounts compared to their interatomic distance, in a cooperative and homogeneous movement, resulting in a new atomic arrangement with a different shape or symmetry. These transformations are both scientifically and technologically important, as they constitute the fundamental strengthening mechanism of steels, and they are directly responsible for the shape memory effect, wherein a deformed alloy "remembers" its original, cold-forged shape and returns to it when heated. The PI will develop and implement efficient computational methods that will allow for calculating various contributions that stabilize atomic arrangements along martensitic transformation paths. Successful completion of the proposed research program will lead to better understanding of the thermodynamic driving forces and atomistic mechanisms of martensitic transformations, hence providing fundamental basis for the rational design of new high-temperature shape memory alloy systems.The educational component of this award involves the education of graduate students and the introduction of undergraduate students to modern computational methods. The PI will partner with the California NanoSystems Institute and the Center X to leverage their ongoing efforts to increase participation of minority students and members of underrepresented groups in engineering, science, and technology. The research will also aid in the improvement of computational science instruction aids via the development of high-throughput molecular dynamics simulations, which is a software platform that aims to streamline the process of performing computer simulations of physical movements of atoms or molecules interacting with each other. The software to be developed will be disseminated freely through the PI's group website.