Microstructural Engineering of Shape Memory Thin Films and Nanowires

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。记得吗它们加热时的原始形状，可以用作致动器。这些材料经历从一种晶体结构到另一种晶体结构的马氏体相变，并提供大的致动力。尽管有这些有趣的特性，形状记忆合金在微机电系统（MEMS）中的集成是有限的，因为激活形状变化的相变的细节对微观结构细节非常敏感。例如，晶粒尺寸的小的增加显著地改变致动力和转变温度。此外，薄膜形式的NiTi的机械行为不同于块体，并且是一个很大程度上未探索的研究课题。该计划的目标是评估晶粒结构，晶粒尺寸和晶粒尺寸分布对相变温度，滞后行为，致动性能和机械性能的影响。因此，我们将探讨NiTi薄膜和纳米结构的结晶行为，并通过检查表现出弹性非线性的材料来拓宽对薄膜机械性能的理解。将通过使用原位透射电子显微镜观察微观结构的发展来研究结构-性能关系。演变和晶粒结构将使用约翰逊？梅尔？阿夫拉米Kolmogorov理论工程微结构的致动特性将与晶片曲率方法和基于MEMS的悬臂梁进行研究;转变温度的变化将与差示扫描量热法进行研究。机械性能对微观结构的依赖性将与纳米压痕检查。这项研究将提供新的观察薄膜形状记忆材料的行为，并提供指导，为他们通过到MEMS.非技术摘要：知识之间的联系相变，微观结构和机械性能将在薄膜中进行研究，通过观察一类新的材料进行马氏体（即位移）转变。通过这项工作，我们将提高对薄膜形状记忆合金的基本理解，并学习如何以可预测的方式控制其性能，从而阐明微观结构对马氏体相变热力学的作用。这种控制性能的能力将使MEMS社区受益，并使未来的设备成为可能。此外，这些材料提供了一个模型来磨练定制微结构的能力，并将有利于非晶硅，无定形碳和金属玻璃的其他研究追求。这个项目？的更广泛的影响包括激发对科学的兴趣，从研究生的培训到学生的鼓励，一系列的个人。经过改进的材料科学入门课程，包括动手演示和现实世界的例子，将培养具有强大材料背景的工程师。在网上传播的课堂演示汇编将为更广泛的学习社区服务。这个教育计划还提供了非正式的机会，通过一系列讲座，展示不同的科学家，并提出愉快的科学活动，改变科学的看法。其目的是鼓励所有学生，特别是有色人种和女孩的学生，把科学作为一种职业。它为学生、教师和家长提供了更丰富的科学联系，是一个简单的模式，可以在大学内部和大学之间推广。通过利用与NISE网络的伙伴关系，该计划将拥有庞大的传播渠道。没有学生落后，这个计划旨在捕捉非科学专业的学生在文科环境中的注意力，利用他们作为示范，以令人信服的方式教科学。

This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARY:Materials like NiTi, which have the unique ability of ?remembering? their original shape when heated, can be used as actuators. These materials undergo a martensitic phase transformation from one crystallographic structure to another and provide large actuation forces. Despite these interesting properties the integration of shape memory alloys in microelectromechanical systems (MEMS) is limited because the details of the phase transformation that activates the shape changes is very sensitive to microstructural details. For example a small increase in grain size significantly changes the actuation force and the transformation temperature. In addition, the mechanical behavior of NiTi in thin-film form differs from the bulk and is a largely unexplored research topic. Objectives of this program are to evaluate the effects of grain structure, grain size and grain-size distributions on phase transformation temperatures, hysteresis behavior, actuation properties, and mechanical properties. Accordingly, we will explore the crystallization behavior of NiTi thin films and nanostructures; and broaden the understanding of thin film mechanical properties by examining materials that exhibit elastic nonlinearities. Structure-property relationships will be studied by observing microstructural development using in situ transmission electron microscopy. Evolution of the and grain structure will be evaluated using the Johnson?Mehl?Avrami?Kolmogorov theory. The resulting actuation properties of the engineered microstructures will be studied with wafer curvature methods and MEMS-based cantilevers; and the transformation temperature changes will be investigated with differential scanning calorimetry. The dependence of mechanical properties on microstructure will be examined with nanoindentation. This study will provide novel observations of the behavior of thin film shape memory materials, and provide guidance for their adoption into MEMS.NON-TECHNICAL SUMMARY:Knowledge of the link between phase transformations, microstructure, and mechanical properties will be studied in thin films by observing a new class of materials that undergo a martensitic (i.e. displacive) transformation. From this work, we will improve the fundamental understanding of thin-film shape memory alloys and learn how to control their properties in a predictable way, thereby illuminating the role of microstructure on the thermodynamics of martensitic transformations. This ability to control properties will benefit the MEMS community and enable future devices. Additionally, these materials provide a model to hone the ability to tailor microstructures and will benefit other research pursuits in amorphous silicon, amorphous carbon, and metallic glasses. This program?s broader impact consists of stimulating the interest in science for a range of individuals from the training of graduate students to the encouragement of school children. A revamped introductory materials science class that includes hands-on demonstrations and real-world examples will cultivate engineers with strong materials backgrounds. A compilation of classroom demonstrations disseminated on the web will serve a wider learning community. This educational program also provides informal opportunities to change the perception of science via a lecture series that showcases diverse scientists and presents enjoyable science events. The aim is to encourage all students, particularly students of color and girls, to consider science as a career. It furnishes richer connections to science for school children, their teachers, and their parents and is a simple model that can be extended within and between universities. By leveraging a partnership with the NISE network, this program will have large dissemination channels. Leaving no student behind, this program seeks to capture the attention of non-science majors in a liberal-arts environment by using them as demonstrators to teach science in a compelling way.