Metallic thin film fatigue dominated by interface character

薄膜由于其在微纳米尺度上所具有的独特特性而被广泛应用。例如，金属薄膜是理想的导电材料，适用于刚性和柔性电子设备和传感器、航天器表面反射镜或微机电系统（MEMS）。在大多数应用中，薄膜是循环加载的，并通过特定的疲劳机制失效。然而，亚微米薄金属薄膜的行为，因此失败，不同于块状材料。这是由于与基体和自由表面之间存在明显的界面，这强烈地影响了与体疲劳有关的位错过程。目前尚未研究的是界面类型如何控制薄膜的疲劳行为。界面可以被认为是硬的，用刚性陶瓷或金属基板创建，软的，靠近聚合物基板，或者薄膜可以没有界面并且是独立的。认为界面类型是控制金属薄膜变形机制和最终破坏的主要参数，是微观结构、屈服强度和循环应力幅值的函数。为了获得薄膜及其特定界面上的变形和破坏信息，需要进行彻底和系统的研究。计划采用先进的原位微力学测试方法，研究界面类型（硬界面、软界面或无界面）对金属薄膜损伤形成和破坏的作用。值得注意的是，使用复杂的原位膨胀测试、x射线衍射技术和透射电子显微镜进行循环力学测试，观察薄膜变形、可能的晶粒生长、挤压形成、薄膜开裂或分层。直接观察将使微观结构响应与界面诱导机制解耦。这些先进的技术和薄膜机械行为方面的专业知识是Friedrich-Alexander University erlangen - n<s:1> rnberg （Benoit Merle博士）和奥地利科学院Erich Schmid材料科学研究所（Megan Cordill博士）拟议合作的基础。各组之间独特的协同作用将使类似样品在独立和不同支撑条件下的疲劳行为的首次系统比较成为可能。有关界面特定失效机制的新知识将用于生成基于机制的薄膜失效模型，并为抗疲劳薄膜应用提供改进的设计标准。

Thin films are used in a wide variety of applications due to the unique properties which are imparted at the micro- and nanoscale. Metal films, for example, are ideal for electrical conduction in rigid and flexible electronics and sensors, reflectors for surface mirrors on spacecraft or micro-electrical-mechanical systems (MEMS). In most applications, thin films are cyclically loaded and fail through specific fatigue mechanisms. However, sub-micrometric thin metal films behave, and thus fail, differently than bulk materials. This has been attributed to the prominent presence of an interface to a substrate and to the free surface, which strongly affects the dislocation processes pertaining to bulk fatigue. What has not yet been examined is how the type of interface controls the fatigue behavior of thin films. Interfaces can be considered as hard, created with a rigid ceramic or metal substrate, soft, next to a polymer substrate, or films can have no interface and be free-standing. It is believed that the interface type is a dominant parameter that controls the deformation mechanisms and final failure of the thin metal films as a function of the microstructure, yield strength and cyclic stress amplitude.In order to obtain deformation and failure information on thin films and their specific interface, a thorough and systematic investigation is required. It is planned to use advanced in-situ micro-mechanical testing methods to examine the role of the interface type, hard, soft or no interface, on the damage formation and failure of thin metal films. Of note is the use of sophisticated in-situ bulge testing, X-ray diffraction techniques and transmission electron microscopy with cyclic mechanical testing to observe film deformation, possible grain growth, extrusion formation, film cracking or delamination. Direct observations will enable the decoupling of the microstructural response from the interface induced mechanisms. These advanced techniques and the expertise on thin film mechanical behavior is the foundation of the proposed collaboration between the Friedrich-Alexander University Erlangen-Nürnberg (Dr. Benoit Merle) and the Erich Schmid Institute of Materials Science of the Austrian Academy of Sciences (Dr. Megan Cordill). The unique synergies between the groups will notably allow the first systematic comparison of the fatigue behavior of similar samples in free-standing and in different supported conditions. The new knowledge about the interface specific failure mechanisms will be used to generate mechanism based models for thin film failure as well as provide improved design criteria for fatigue resistant thin film applications.