Magnetic shape memory alloys change shape when exposed to a variable magnetic field through the movement of twin boundaries. To exhibit these behaviors, the material must be grown as a single crystal. The growth process is performed with a furnace at very particular temperatures and cooling rates. Deviation from ideal process parameters causes the formation of defects such as small angle grain boundaries. Such defects reduce the actuation performance of magnetic shape memory alloys. For example, they reduce the actuation strain, nucleate cracks, and shorten the operation life time. Minimizing or eliminating the formation of small angle grain boundaries would produce true single crystals, which would perform much better as magnetic shape memory alloy samples. Here, we analyze some of the various causes of small angle grain boundary formation, the impact of small angle grain boundaries on the properties and performance of Ni-Mn-Ga samples, and strategies to avoid their formation.
Freilich, Justina, "Development of Small Angle Grain Boundaries During Single Crystal Growth Process of Ni-Mn-Ga" (2016). 2016 Undergraduate Research and Scholarship Conference. Paper 10.