Papers by Keyword: Ni₂MnGa Alloy

Abstract: Ferromagnetic shape memory alloys can produce large strains in a magnetic field by twin boundary motion. The mobility of parent-martensite inter-phase interfaces and twin-twin inter-variant boundaries is closely related to their interfacial structures and the mechanism of migration, therefore a thorough understanding of its nature is of importance. A physical model of the structure of parent-martensite interface has been developed recently based on dislocation theories and topological arguments. On the basis of the topological model, the present work performs a theoretical study of the defect structure of the martensitic interface, and the transformation crystallography in Ni₂MnGa alloy. The habit plane, i.e., the parent-martensite interface plane was determined to be (-0.761, -0.054, -0.646)_P for the parent crystal index frame, and (-0.818, 0.067, -0.571)_M for the martensite frame. The habit plane inclination angle is 5.945° and 5.953° with respect to the terrace plane in the parent and martensite crystals, respectively.

Abstract: Transmission electron microscopy studies of the Ni2MnGa alloy showed that in the diffraction patterns there exist two additional effect apart from the spots given by the parent L21 Heusler phase and the tetragonal no modulate martensite. The first effect was the presence of sharp extra spots, lying on a direction significantly deviated from the <110>* for [001]β zone axis. These spots are connected with modulation of the parent phase. The value of the deviation angle is about 11-12°. The detailed analysis showed that the direction of the propagation vector of modulation is <641> type direction. The second effect visible in the [001]β diffraction patterns is the presence of the arcs located between the 220 type parent phase spots.. The analysis of this objects suggests that some chemical modulation exists with the period of <550>β. In this case short range ordering plays the essential role.