Self-accommodation in polycrystalline 10M Ni-Mn-Ga martensite

摘要

10M Ni-Mn-Ga polycrystals show a typical self-accommodated microstructure consisting of macro and micro twins. The macro twin lamellae separate micro twins creating a so-called "twins within twins" microstructure. Such a configuration allows the distribution of martensitic variants with no net change in shape of the sample. The arrangement of variants can occur on different length scales, from a few nanometers up to a few millimeters, not only depending on grain size but also on processing condition (e.g., extrusion, torsion). Small austenite grains do not completely transform to martensite giving rise to some residual austenite. Furthermore, characteristic branching of macro and micro twins is observed due to lowering of the elastic energy at grain and macro twin boundaries, respectively.