Shape memory behavior of Ni-Fe-Ga and Ni-Mn-Sn ribbons

Abstract

Abstract. Magnetic Shape Memory Alloys exhibit multifunctional properties due the martensitic transformation (MT) and accompanying changes in the magnetic subsystem. In this work, melt spun ribbons of nominal composition Ni55Fe16Ga29 (R1) and Ni50Mn40Sn10 (R2) have been produced and characterized by the calorimetric, thermomechanical, mechanical, microscopic and X-ray measurements. The effect of short annealing on MT and thermo-mechanical properties is rather modest and in the case of R2 enhances its brittleness. R1 and R2 as-spun ribbons show MT at TM ~ 340 K and ~ 420 K, respectively. The strain-stress curves for Ni-Fe-Ga in austenitic phase indicate good visco-elastic properties, although the superelastic effect was not well pronounced. Ni-Fe-Ga as-cast and annealed samples, as well as the as-cast Ni-Mn-Sn ribbons, present a shape memory effect with an anomalous contraction and elongation at low external stresses in the course of the forward and reverse MT, consequence of the compressive internal stresses.

Temperature Dependent Stress–Strain Behavior and Martensite Stabilization in Magnetic Shape Memory Ni51.1Fe16.4Ga26.3Co6.2 Single Crystal

“…Figure 2a displays the twinning stress required for the variant reorientation in the martensitic phase at T < A s (open squares) and the critical stress of the stress-induced MT at T > A f (solid circles). It is seen that, while the twinning stress is slightly decreasing with the temperature, the critical stress for stress-induced MT linearly increases as a function of the temperature with a slope of 3.6 MPa/ • C. This value is in line with those found in other Ni-Fe-Ga-based FSMAs [33,40]. It is easy to find that the extrapolated temperature value at zero stress, which gives the transformation temperature from the thermally induced martensite to the austenite, is in a good agreement with the DSC results (69 • C) (see Table 1).…”