Regularities of functional properties in stress-induced martensite aged single crystals of Ni₅₁Fe₁₈Ga₂₇Co₄ ferromagnetic alloy

In the present work, the effect of plastic deformation during the preliminary superelasticity cycle and/or during the stress-induced martensite aging (SIM-aging) process on the two-way shape memory effect (TWSME) and rubber-like behavior (RLB) in β- and (β+γ)-single crystals of Ni₅₁Fe₁₈Ga₂₇Co₄ alloy with thermoelastic L 2₁( B 2)-10M/14M- L 1₀ martensitic transformations was studied. It was experimentally shown that the SIM-aging along the [110]_B2-orientation at T = 423 K for 1 hour under a compressive stress 430 MPa (for β-crystals) and 400 MPa (for (β+γ)-crystals) induces the large reversible strains along the perpendicular [001] _B2-orientation at stress-free cooling/heating cycles (TWSME) and loading/unloading at T < A _s (RLB). The chemical stabilization of L 1₀-martensite in SIM-aged β-crystals leads to the appearance of TWSME with reversible strain ε_TWSME1 = +8.1% due to the oriented growth of martensite in thermal cycles and RLB with reversible strain ε_RLB1 = -14.2% caused by reorienting martensitic variants by moving twin boundaries in compression. The presence of plastic deformation contribution in the preliminary superelasticity cycle and/or in the SIM-aging process in (β+γ)-crystals leads to a combination of chemical and mechanical stabilization of L 1₀-martensite. As a result, in the SIM-aged (β+γ)-crystals, firstly, the TWSME strain (ε_TWSME2 = +4.5%) is 1.8 times less than in β-crystals. Secondly, loading/unloading cycles of RLB with a reversible strain of ε_RLB2 = -13.2% are accompanied by high values of the critical stresses for reorientation of martensitic variants σ_cr2 = 55 MPa and dissipation energy ΔG_irr2 = 924 J/m³, in contrast to β-crystals for which σ_cr1 = 12 MPa and Δ G _irr1 = 456 J/m³. This is due to the contribution of mechanical stabilization of L 1₀-martensite and the pinning of interphase and twin boundaries by dislocations in SIM-aged (β+γ)-crystals.

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