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 - 标准是在许多技术上重要的金属和陶瓷中发生的结构变化的产物。调制的马氏体是一种由一系列原子层组成的马氏体，通常与医用植入物和消费产品中使用的形状内存合金的异常特性有关。尽管调制马氏体具有科学和工程的重要性，但关于其结构的问题仍未解决。与大多数金属合金不同，调制的马氏体的原子结构在单晶或谷物中各不相同。原子结构还响应施加的应力，温度变化或磁场而变化很容易变化。该项目采用两种互补的实验技术来阐明模型调制的马氏体的结构。研究团队正在使用三维X射线散射来确定从数十纳米到微米的长度尺度上的平均原子结构，以及三维透射电子显微镜，以揭示各个区域内几种纳米纳米的原子结构。这两种技术的组合提供了有关原子层跨多个长度尺度的周期性的信息 - 这两种技术都无法通过任何两种技术获得。该方法适用于具有准周期调制的多种材料，它减少了艰苦的高分辨率电子显微镜的需求（目前，原子尺度表征的首选技术，但昂贵且耗时）。参与该项目的学生是学习用于开发新材料的重要实验，计算和理论工具。技术描述调制的Martensite的结构性，这些结构具有长期周期分层结构和静脉堆积序列，这是一个基本问题，是一个争议的基本问题。这项协作研究阐明了具有互补实验技术的调制马氏体：三维（3D）同步加速器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晶格调制的多个时期的空间尺度上的原子堆叠。该项目使用Ni-MN-GA作为调制马氏体的模型系统，解决了一些基本问题：它们如何形成，为什么它们是稳定的，它们是衍射模式是由于在扩展体积上平均或反映局部原子秩序以及它们如何随温度，压力，压力，磁场和影响Slabe Memory Elloys的伪弹性属性而产生的。研究的目标和范围是：（1）对Argonne National Lab的高级光子源的Ni-MN-GA单晶进行3D衍射测量； （2）分析3D散射强度数据，以确定使用原子尺度反向蒙特卡洛和纳米温微结构细化方法来确定原子尺度的晶格调制； （3）在一系列方向下，从小晶体体积进行高分辨率电子显微镜，Lorentz显微镜和纳米束电子衍射，以将晶格调制，磁性域和相互的空间图相关联； （4）开发一种通过结合确定的转化机制来描述马氏体和马氏体间转化行为的模型。