Strength Design Maps for Nanoscale Metallic Multilayer Thin Films

技术：纳米多层薄膜是研究结构-力学性能关系的非凡体系。首先，这些体系显示出显著的强度，远远超过具有相当晶粒尺寸的单相体系的强度。其次，合成方法允许对成分和微观结构进行前所未有的控制，因此它们已成为研究结构，化学，界面和物理性质（如强度）之间相关性的试验台。对于金属系统，这种强度取决于将滑移限制在小体积内的能力。目前，还没有系统的方法来预测这类系统的屈服强度，也没有相应的系统验证方法。因此，在涉及MEMS、硬涂层、折射光学元件、半导体带隙以及磁弹性和磁光学薄膜的应用中，多层薄膜界缺乏广泛的设计策略来优化屈服强度。该计划的总体目标是开发和验证A/B金属多层薄膜的屈服强度设计图。这些图将包括作为输入的单个相位特性、双层周期、体积分数、外延关系和外部负载的方向/符号。该方法是通过先进的基于三维位错的模拟技术、位错理论和新颖的实验验证方法的组合程序来推进当前的预测方法。其中包括通过x射线衍射测量验证内应力图；透射电镜研究界面位错含量图的验证并通过新型微柱测试和薄膜/基材弯曲测试验证屈服强度设计图。屈服强度设计图体现了对体积、面积和线能如何驱动界面结构和内应力状态的基本理解，以及这些特征如何将晶体滑移限制在小体积内。模型和实验结果的比较将提供目前无法获得的位错线能、内应力大小和界面势垒强度的值。几个科学前提将被检查，包括屈服强度优化的具体策略。非技术：所提出的工作将推动纳米层薄膜材料领域的发展。它还将加强教学、培训和学习的使命，促进代表性不足群体的参与和专业发展。

Technical: Nanoscale multilayer thin films are extraordinary systems with which to study structure-mechanical property relations. First, these systems display remarkable strength, far surpassing the strength of single-phase systems with comparable grain size. Second, the methods of synthesis allow for unprecedented control of composition and microstructure, so that they have become a test bed to study correlations between structure, chemistry, interfaces, and physical properties such as strength. For metallic systems, that strength hinges on the ability to confine slip to small volumes. Currently, there exists no systematic means by which to predict yield strength in such systems, nor does a corresponding approach for systematic validation exist. Consequently, the multilayer thin film community lacks a broad design strategy to optimize yield strength in applications involving MEMS, hard coatings, refractive optical elements, band gaps for semiconductors, and magneto-elastic and magneto-optical films. The overall aim of the proposed program is to develop and validate yield strength design maps for A/B metallic multilayer thin films. These maps will include as input the individual phase properties, bilayer period, volume fractions, epitaxial relationships, and direction/sign of external loading. The approach is to advance current predictive methods through a combined program of advanced 3D dislocation-based simulation techniques, dislocation theory, and novel experimental verification methods. These include verification of internal stress maps via x-ray diffraction measurements; verification of interfacial dislocation content maps via transmission electron microscope studies; and verification of yield strength design maps via novel micropillar testing and film/substrate bend testing. Yield strength design maps embody a fundamental understanding of how bulk, area, and line energies drive interfacial structure and internal stress state and further, how these features confine crystallographic slip to small volumes. The comparison of modeling and experimental results will provide values of dislocation line energies, internal stress magnitudes, and interfacial barrier strengths that are not currently available. Several scientific premises will be examined, including specific strategies for yield strength optimization.Non-technical: The proposed work will advance the field of nanolayered thin-film materials. It will also strengthen the mission of teaching, training, and learning and promote the participation and professional development of underrepresented groups.