Microstructure and martensitic transformation behavior of Ni-Mn-Fe-Ga-B high-temperature shape memory melt-spun ribbons

The microstructure and martensitic transformation behavior of (Ni56Mn17Fe8Ga19)(99.8)B-0.2 and (Ni56Mn16Fe9Ga19)(99.8)B-0.2 high-temperature shape memory melt-spun ribbons Were studied. The results show that the rapidly melt-spun process is an effective method to refine the grain size of NiMnGa-based alloys. It is also found that the rapidly melt-spun process restrains the formation of gamma phase in the as-spun ribbons. However, when the as-spun ribbons are annealed at 600 degrees C, the gamma phase preferentially forms and distributes along the grain boundaries between martensite variants. This result is different from that of the as-quenched buttons, where the gamma phase randomly distributes within the martensite. These obtained results may provide useful information for improving the ductility and shape memory effect of NiMnGa-based alloys. Results further show that the martensitic transformation temperatures of the as-spun ribbons and the as-annealed ribbons are obviously higher than those of the as-quenched buttons due to an increase in the electron concentration of martensite and the martensite stabilization induced by the rapidly melt-spun process. (C) 2012 Elsevier B.V. All rights reserved.