NSF-Europe Materials Collaboration: Micromechanics of Magnetic Shape-Memory Alloys

这项研究的目的是提高我们对控制裂纹形核、断裂和在循环载荷下磁性形状记忆合金(MSMA)可靠性的基本知识。正在研究的是在循环磁机械驱动过程中导致损伤的微观结构特征，目的是在循环磁机械驱动中优化长寿命的微结构。为了达到这一目标，对不同微结构的Ni-Mn-Ga晶体在旋转磁场中的力学响应进行了评估。使用一套定义的热-磁-机械处理来系统地修改微结构。然后使用各种方法，包括高分辨率电子显微镜、磁力显微镜和X射线衍射，在原子、介观和宏观尺度上对微观结构进行表征。利用专用试验机对MSMA的动态磁力学性能进行了系统的研究。在此基础上，建立了一个定量的、基于缺陷的细观力学模型，用于预测循环磁加载过程中裂纹的形成。智能的优点是扩展了我们对控制磁性形状记忆合金执行器的性能和可靠性的机制和微结构特征的基本知识。控制它们的性能和可靠性是将这些材料应用于工业应用的关键。要实现这一目标，需要从微观上理解磁塑性，控制微结构的形成，以及适当的表征方法来量化MSMA对磁场的机械响应。这项研究将把原子尺度上的缺陷描述、介观尺度上的微观结构和宏观尺度上的磁力学性能联系起来，从而对磁性形状记忆合金有一个基本的了解。更广泛的影响包括支持博伊西州立大学最近成立的材料系的一个创新材料研究项目。该课程强调将经典材料科学原理应用于一类新兴材料的研究。这一努力将促进以研究为基础的教育，并将提供一种国际化的、协作的工作体验。参与该项目的本科生和研究生将访问国外，并在苏黎世联邦理工学院工作。学生们将参加由国际和平协会联合举办的国际研讨会。预期的研究成果将有助于开发MSMA在医学、交通、国防和环境保护方面的应用。

The goal of this study to improve our basic knowledge of those factors that control crack nucleation, fracture, and reliability under cyclic loading of magnetic shape-memory alloys (MSMA). Under examination are the microstructural features that incur damage during cyclic magnetomechanical actuation with the goal of optimizing the microstructure for long lifetime in cyclic magneto-mechanical actuation. To reach this goal, mechanical response is evaluated for Ni-Mn-Ga crystals of differing microstructures that are exposed to rotating magnetic fields. The microstructure is systematically modified using a set of defined thermo-magneto-mechanical treatments. The microstructure is then characterized on an atomistic, mesoscopic and macroscopic scale using a variety of methods, including high-resolution transmission electron microscopy, magnetic force microscopy, and X-ray diffraction. A systematic study of the dynamical magneto-mechanical properties of MSMA is performed using a dedicated testing machine. Based on the results, a quantitative, defect-based, micromechanistic model will be developed that predicts the formation of cracks during cyclic magnetic loading. The intellectual merit is to expand our basic knowledge of the mechanisms and microstructural characteristics that control the performance and reliability of magnetic shape memory alloy actuators. Controlling their performance and reliability is critical for applying these materials to industrial applications. Achieving this goal requires a micromechanistic understanding of magnetoplasticity, control of microstructure formation, and suitable characterization methods to quantify the resulting mechanical response of MSMA to magnetic fields. This research will link defect description at the atomistic scale, microstructures at the mesoscopic scale, and magneto-mechanical properties at the macroscale, leading to a fundamental understanding of magnetic shape-memory alloys. The broader impact includes the support of an innovative materials research program in the recently established Materials Department at Boise State University. The program emphasizes the application of classical materials science principles in the investigation of an emerging class of materials. This effort will foster research-based education and will provide an international, collaborative work experience. Undergraduate and graduate students working on the project will visit and work abroad at the Swiss Federal Institute of Technology, ETH Zurich. Students will participate in an international workshop co-organized by the PI. The anticipated research results will be instrumental in developing MSMA applications in medicine, transportation, defense, and environmental protection.