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

技术支持：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。高风险在于提取纳米孪晶微结构的定量信息的未经测试的新颖想法（即，主要厚度和变化的体积分数，以及它们的统计变化）。这种纳米孪晶微结构是一种高度异质的系统，产生不寻常的衍射图案，不能用传统的粗畴衍射理论来解释。这个想法的动机是一个新发现的，以前未探索的纳米孪晶衍射现象，最近由PI的初步纳米孪晶衍射理论揭示，这表明超晶格反射峰的异常位置，形状，宽度和强度包含有关纳米孪晶微观结构的定量信息，并可以进行分析，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极有希望的机会。该SGER项目将使用铁磁形状记忆合金Ni-Mn-Ga中不同周期的纳米孪晶（通常称为多个长周期层状马氏体相）作为模型系统，并执行小规模临界实验和理论/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，以基准新的实验技术。非技术性：如果成功，回报是高的：它将开发一种变革性的实验技术，通过使用简单的原位衍射进行定量纳米孪晶微结构表征，为“既定”衍射研究开辟新的方向，并催化纳米材料实验研究的快速进展。特别是，这项新技术将使用更容易的原位衍射来至少部分取代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，这是艰苦的，昂贵的和耗时的。这一新的实验技术将为纳米材料的表征提供一种新的、强有力的、方便的实验工具，从而促进我们对许多重要功能材料中纳米畴现象的理解。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，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.