Martensitic transformation in melt-spun Ni-Mn-Ga ribbons

Off-stoichiometric Ni-Mn-Ga alloys, with various chemical compositions, were produced by melt-spinning technique. Transformation behavior was studied by means of differential scanning calorimetery (DSC). Ribbons and bulks reveal reversible martensitic transformation which occurs, dependently on chemical composition, in the range of temperatures: between 100 degrees C and -150 degrees C. Transmission electron microscope and X-ray diffractometer were used for structure examination. Dependently on chemical composition five-layered (10 M) or seven-layered (14 M) martensite was observed, whereas the parent phase shows the B2 structure. Due to high cooling rate realized in melt-spinning technique some amount of amorphous phase was found. For all ribbons magnetization was measured versus change of temperature as well as magnetic field. Due to relatively high density of dislocations lower value of magnetization were obtained.