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，利用原位X射线和中子衍射来定量表征纳米孪晶微结构及其在外加应力、电场和/或磁场下的实时演化。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结构的定量信息(即主要厚度和不同体积分数，以及它们的统计变化)这一未经检验的新颖想法。这种纳米孪晶微结构是一个高度不均匀的系统，产生了无法用传统的粗晶区衍射理论解释的特殊衍射图案。这一想法是由最近PI的初步纳米孪晶衍射理论揭示的一种新发现的、以前未被探索的纳米孪晶衍射现象所激发的，该现象表明，超晶格反射峰的异常位置、形状、宽度和强度包含了关于纳米孪晶微结构的定量信息，可以进行分析，从而为探索性研究开发新的纳米孪晶衍射分析技术创造了一个非常有希望的机会。这项SGER计划将使用铁磁形状记忆合金Ni-Mn-Ga中不同周期的纳米孪晶(传统上称为多个长周期层状马氏体相)作为模型系统，并执行小规模的关键实验和理论/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，以对新的实验技术进行基准测试。非技术性：如果成功，回报是高的：它将开发一种通过简单的原位衍射来定量表征纳米孪晶微结构的变革性实验技术，为已经建立的衍射研究开辟一个新的方向，并促进纳米材料实验研究的快速发展。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是目前唯一能够表征纳米结构域的工具，但对于分析许多样品来说，这是费力、昂贵和耗时的。这项新的实验技术将为纳米域材料的表征提供一种新的、强大的、方便的实验工具，进而将加速我们对许多重要功能材料中的纳米域现象的理解。该项目将通过为参与者提供从事最先进的探索性研究的机会，为人力资源开发做出贡献。

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.