SGER: Developing a New Experimental Technique for Quantitative Nanotwin Microstructure Characterization by Using In-Situ Diffraction

技术：该SGER项目将开发一种新的实验技术，使用原位x射线和中子衍射来定量表征纳米孪晶微观结构及其在外加应力、电场和/或磁场下的实时演变。这是一项高风险、高回报的研究。高风险在于从衍射图中提取纳米孪晶微观结构的定量信息（即优势厚度和不同体积分数，以及它们的统计变化）的想法未经检验和新颖。这种纳米孪晶结构是一种高度非均质系统，产生了传统的粗畴衍射理论无法解释的异常衍射模式。这一想法的灵感来自于一个新发现的、以前未被探索的纳米孪晶衍射现象，该现象最近被PI的初步纳米孪晶衍射理论所揭示，该理论表明，超晶格反射峰的异常位置、形状、宽度和强度包含了纳米孪晶微观结构的定量信息，并且可以被分析，从而为开发新的纳米孪晶衍射分析技术的探索性研究创造了一个非常有希望的机会。该SGER项目将以铁磁形状记忆合金Ni-Mn-Ga中不同周期（通常称为多个长周期层状马氏体相）的纳米孪晶为模型系统，并进行小尺度的关键实验和理论/计算任务，即高分辨率透射电子显微镜（HRTEM）， x射线和中子衍射，纳米孪晶衍射理论和计算，对新的实验技术进行基准测试。非技术：如果成功，回报是高的：它将发展一种革命性的实验技术，通过简单的原位衍射来定量表征纳米孪晶的微观结构，为“既定”的衍射研究开辟一个新的方向，并催化纳米畴材料的实验研究取得快速进展。特别是，新技术将使用更容易的原位衍射至少部分取代HRTEM， HRTEM是目前唯一能够进行纳米畴表征的工具，但对于分析许多样品来说是艰苦，昂贵且耗时的。新的实验技术将为纳米畴材料的表征提供一种新的、强大的、方便的实验工具，从而加快我们对许多重要功能材料中纳米畴现象的理解。该项目将为参与者提供从事最先进的探索性研究的机会，从而促进人力资源开发。

TECHNICAL: This SGER project will develop a new experimental technique to use in-situ x-ray and neutron diffractions to quantitatively characterize nanotwin microstructures and their real-time evolutions under applied stress, electric and/or magnetic fields. This is a high-risk and high-payoff research. The high risk lies in the untested and novel idea of extracting quantitative information of nanotwin microstructures (i.e., dominant thicknesses and variant volume fractions, and their statistical variations) from the diffraction patterns. Such a nanotwin microstructure is a highly heterogeneous system producing extraordinary diffraction patterns that cannot be explained by the conventional diffraction theory of coarse domains. The idea is motivated by a newly discovered, previously unexplored nanotwin diffraction phenomenon as recently revealed by the PI's preliminary nanotwin diffraction theory, which shows that the unusual position, shape, width and intensity of the superlattice reflection peaks contain the quantitative information about nanotwin microstructures and could be analyzed, thus creating a highly promising opportunity for the exploratory research to develop new nanotwin diffraction analysis technique. This SGER project will use the nanotwins of various periods (conventionally known as multiple long-period layered martensitic phases) in ferromagnetic shape memory alloy Ni-Mn-Ga as model system and perform small-scale critical experimental and theoretical/computational tasks, namely, high-resolution transmission electron microscopy (HRTEM), x-ray and neutron diffraction, nanotwin diffraction theory and computation, to benchmark the new experimental technique. NON-TECHNICAL: If successful, the payoff is high: it will develop a transformative experimental technique for quantitative nanotwin microstructure characterization by using simple in-situ diffraction, open a new direction for the "established" diffraction research, and catalyze rapid advances in experimental investigation of nanodomained materials. In particular, the new technique will use the much easier in-situ diffraction to at least partially replace HRTEM, which is currently the only tool capable of nanodomain characterization, but is painstaking, costly and time-consuming impractical for analyzing many samples. The new experimental technique will provide a new, powerful and convenient experimental tool for nanodomained materials characterization, which will, in turn, expedite our understanding of nanodomain phenomena in many important functional materials. The project will contribute to human resource development by providing opportunity for participants to work on state-of-the-art exploratory research.