Compressive shape memory actuation response of stress-induced martensite aged Ni51Fe18Ga27Co4 single crystals

In the present study, the effects of stress-induced martensite aging (SIM-aging) in twinned L1(0)-martensite on the functional properties of [001](A)-oriented Ni51Fe18Ga27Co4 (at%) single crystals were systematically investigated. SIM-aging of as-grown single crystals with gamma-phase precipitates at T-SIM = 448 K for 1 h, under a compressive stress sigma(SIM) of 700 MPa along the [001](A)parallel to[110](M)-direction, leads to an increase in the martensitic transformation temperatures M-s and A(f) by 60(+/- 3) K and induces a two-way shape memory effect with a reversible strain up to -3.4(+/- 0.3)%. Moreover, the SIM-aged crystals demonstrate a 1.5- to 2-fold decrease in the thermal and stress hysteresis as compared to the as-grown crystals. The SIM-aged crystals feature a narrow stress hysteresis and the high cyclic stability of superelasticity at elevated temperature up to 420 K. Thus, these materials are attractive for use as efficient high-temperature actuators. The physical reasons for martensite stabilization in the Ni51Fe18Ga27Co4 single crystals, such as the symmetry-conforming adaptation of the short-range order, the pinning of moving interfaces by defects, and the plastic deformation of gamma-phase precipitates during SIM-aging, are discussed.