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.
