Analysis Method of Twin Boundary Motion in Ni-Mn-Ga Micropump

Shape memory alloys undergo reversible plastic deformation through twin boundary motion under a stress. Magnetic shape memory (MSM) alloys such as Ni-Mn-Ga can be actuated mechanically and magnetically. Researchers at Boise State University’s Magnetic Materials Laboratory developed a motionless micropump based on MSM actuation principles. To optimize the MSM micropump and gain a better understanding of the nature of twin boundary motion, videos were taken of the actuating member under a microscope while a varying magnetic field swept the MSM actuation member. In order to sweep and track the angle of the magnetic field a fixture was built. This allowed for an accurate study of the actuating member under pump like conditions. Due to the visual nature of this microscopy technique, the high reflectivity of the metal surface and the speed of the twin boundaries hamper the characterization of twin boundary motion. We quantified twin boundary velocity with a frame-by-frame analysis of the position of twin boundaries. This is an ongoing project that is anticipated to produce both qualitative and quantitative results on twin boundary motion. The results will inform the design optimization of the MSM micropump. Preliminary results show a dynamic widening and narrowing of twins as the magnetic field is swept through the MSM element