On the high cyclic stability of the tensile two-way shape memory effect in stress-induced martensite aged Co35Ni35Al30 single crystals

Highlights: • Stress-induced martensite ageing results in cyclically stable two-way shape memory. • Stress-free thermal cycling does not affect the two-way shape memory characteristics. • Applied of opposing stress above ageing temperature leads to property degradation. A stable tensile two-way shape memory effect with a strain of (+7.0 ± 0.3) % along the [001]_B2-direction upon stress-induced martensite ageing was obtained for single crystals of an Co₃₅Ni₃₅Al₃₀ ferromagnetic alloy. Stress-induced martensite ageing at 398 K for 1.0 h under a compressive stress of 500 MPa along the [110]_B2-direction led to the stabilization of L1₀-martensite variant, which contributes to sample elongation along the [001]_B2-direction during stress-free cooling and reversible recovery upon subsequent heating. The tensile two-way shape memory effect was observed to be stable during stress-free thermal cycling through the phase transformation range. The characteristics of the two-way shape memory effect (reversible strain, martensitic transformation temperatures, and thermal hysteresis) did not change during 100 thermal cycles. The characteristics of the tensile two-way shape memory effect remain unchanged even after superelasticity cycling under a compressive stress of 1025 MPa applied along the [001]_B2-direction at a temperature of 423 K, which is close to the stress-induced martensite ageing temperature.