Collaborative Research: In-Situ Three-Dimensional Diffraction and High-Resolution Electron Microscopy Study of Modulated Martensites

合作研究：调制马氏体的原位三维衍射和高分辨率电子显微镜研究

• 批准号: 1506936
• 负责人: Yu Wang
• 金额: $ 27.35万
• 依托单位: Michigan Technological University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506936&HistoricalAwards=false
• 关键词: Collaborative; Research; Situ; Three; Dimensional

Nontechnical DescriptionMartensite is the product of a structural change that occurs in many technologically important metals and ceramics. Modulated martensite is a type of martensite composed of a sequence of atomic layers, and it is often associated with the unusual properties of shape memory alloys used in medical implants and consumer products. Despite the scientific and engineering importance of modulated martensite, there are unanswered questions about its structure. Unlike in most metallic alloys, the atomic structure of modulated martensite varies within a single crystal or grain. The atomic structure also changes rather easily in response to applied stress, temperature change, or magnetic field. This project employs two complementary experimental techniques to clarify the structure of a model modulated martensite. The research team is using three-dimensional X-ray scattering to determine the average atomic structure over length-scales ranging from tens of nanometers to micrometers, and three-dimensional transmission electron microscopy to reveal the atomic structure within regions a few nanometers across. The combination of the two techniques provides information on the periodicity of atomic layers across multiple length scales - data that cannot be obtained by either technique in isolation. The approach is applicable to many kinds of materials with quasi-periodic modulations, and it reduces the need for painstaking high-resolution electron microscopy (currently the technique of choice for atomic-scale characterization, but costly and time-consuming). Students involved in the project are learning important experimental, computational, and theoretical tools used to develop new materials.Technical DescriptionThe structural nature of modulated martensites that exhibit long-period layered structures and aperiodic stacking sequences is a fundamental issue surrounded by controversy. This collaborative research sheds light on modulated martensites with complementary experimental techniques: three-dimensional (3D) synchrotron X-ray diffraction and high-resolution electron microscopy. It clarifies atomic stacking on spatial scales ranging from a few atomic planes to multiple periods of the lattice modulations. Using Ni-Mn-Ga as a model system for modulated martensite, this project addresses some fundamental questions: how they form, why they are stable, whether their diffraction patterns arise from averaging over an extended volume or reflect local atomic order, and how they evolve with temperature, stress, magnetic field and affect pseudoelastic properties of shape memory alloys. The goals and scope of the research are to: (1) perform 3D diffraction measurements on Ni-Mn-Ga single crystals at the Advanced Photon Source of Argonne National Lab; (2) analyze the 3D scattering intensity data to determine atomic-scale lattice modulations using atomic-scale reverse Monte Carlo and nanotwin microstructure refinement methods; (3) perform high-resolution electron microscopy, Lorentz microscopy and nanobeam electron diffraction from small crystal volumes at a series of orientations to correlate lattice modulations, magnetic domains and reciprocal space maps; and (4) develop a Landau-type model to describe the martensitic and inter-martensitic transformation behaviors by incorporating the identified transformation mechanisms.

非技术描述马氏体是许多具有重要技术意义的金属和陶瓷中发生的结构变化的产物。调制马氏体是一种由一系列原子层组成的马氏体，它经常与医疗植入物和消费品中使用的形状记忆合金的特殊性能有关。尽管调制马氏体在科学和工程上具有重要意义，但关于其结构仍有一些悬而未决的问题。与大多数金属合金不同，调制马氏体的原子结构在单晶或单晶内变化。原子结构也很容易随着外加应力、温度变化或磁场的变化而变化。本项目使用两种互补的实验技术来阐明模型调制马氏体的结构。研究小组正在使用三维X射线散射来确定从几十纳米到微米的长度范围内的平均原子结构，并使用三维透射电子显微镜来揭示几纳米范围内的原子结构。这两种技术的结合提供了有关原子层在多个长度尺度上的周期性的信息--这些数据不能通过这两种技术中的任何一种单独获得。这种方法适用于许多具有准周期调制的材料，并且它减少了对费力的高分辨率电子显微镜的需要(目前原子尺度表征的技术是选择的，但昂贵且耗时)。参与该项目的学生正在学习用于开发新材料的重要的实验、计算和理论工具。技术描述调制马氏体的结构性质表现出长周期的层状结构和非周期的堆积序列，这是一个围绕着争议的基本问题。这项合作研究用互补的实验技术揭示了调制马氏体：三维(3D)同步X射线衍射和高分辨率电子显微镜。它阐明了从几个原子平面到多个晶格调制周期的空间尺度上的原子堆积。利用Ni-Mn-Ga作为调制马氏体的模型体系，解决了一些基本问题：它们是如何形成的，为什么它们是稳定的，它们的衍射图是来自扩展体积的平均还是反映了局域原子的有序，以及它们是如何随着温度、应力、磁场的演化而变化以及对形状记忆合金的伪弹性性质的影响。研究的目标和范围是：(1)在Argonne国家实验室的高级光子源对Ni-Mn-Ga单晶进行三维衍射测量；(2)利用原子尺度的逆蒙特卡罗方法和纳米孪晶微结构精化方法，分析3D散射强度数据，以确定原子尺度的晶格调制；(3)从小晶体体积的一系列取向进行高分辨率电子显微镜、洛伦兹显微镜和纳米束电子衍射，以将晶格调制、磁畴和倒易空间图关联起来；(4)通过纳入已知的相变机制，建立Landau模型来描述马氏体和马氏体间的相变行为。