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

本研究的目的是提高我们的基本知识，这些因素控制裂纹的成核，断裂，和循环载荷下的磁性形状记忆合金（MSMA）的可靠性。在检查中的微观结构特征，在周期性的磁力致动过程中产生的损害，在周期性的磁力致动的目标是优化的微结构的长寿命。为了达到这一目标，机械响应评估不同的微观结构，暴露于旋转磁场的Ni-Mn-Ga晶体。使用一组定义的热-磁-机械处理系统地修改微观结构。然后，使用各种方法，包括高分辨率透射电子显微镜，磁力显微镜和X射线衍射的原子，介观和宏观尺度上的微观结构的特征。使用专用的测试机的动态磁机械性能的MSMA进行了系统的研究。基于这些结果，将开发一个定量的、基于缺陷的微观力学模型，该模型预测循环磁加载过程中裂纹的形成。智力的优点是扩大我们的基本知识的机制和微观结构的特点，控制性能和可靠性的磁性形状记忆合金执行器。控制其性能和可靠性对于将这些材料应用于工业应用至关重要。实现这一目标需要对磁塑性的微观力学理解，微观结构形成的控制，以及合适的表征方法来量化MSMA对磁场的机械响应。这项研究将链接在原子尺度上的缺陷描述，在介观尺度上的微观结构，在宏观尺度上的磁机械性能，导致磁性形状记忆合金的基本理解。更广泛的影响包括对博伊西州立大学最近成立的材料系的创新材料研究计划的支持。该计划强调经典材料科学原理在新兴材料类调查中的应用。这一努力将促进以研究为基础的教育，并将提供国际合作的工作经验。从事该项目的本科生和研究生将访问瑞士联邦理工学院，苏黎世。学生将参加由PI共同组织的国际研讨会。预期的研究结果将有助于开发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.