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 (Ni ₅₆Mn₁₇Fe₈Ga₁₉)_99.8B _0.2 and (Ni₅₆Mn₁₆Fe₉Ga ₁₉)_99.8B_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 γ phase in the as-spun ribbons. However, when the as-spun ribbons are annealed at 600 °C, the γ 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 γ 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.