Effect of the Stress-Induced Martensite Aging Time on the Functional Properties of Heterophase Ni49Fe18Ga27Co6 Single Crystals.

This work studies the effect of the stress-induced martensite aging at T = 423 K for 1 and 3 h under compressive stress |σ| = 520–590 MPa on the two-way shape memory effect, superelasticity, and elastocaloric effect in [001]_L21-oriented Ni₄₉Fe₁₈Ga₂₇Co₆ ferromagnetic alloy single crystals containing dispersed γ(γ′)-phase particles. Experiments showed that stress-induced martensite aging causes the two-way shape memory effect, an increase in martensite start temperatures by 64–89 K, and a decrease in strains and stress hysteresis under superelasticity conditions during compression. As the stress-induced martensite aging time increases from 1 to 3 h, the reversible strain increases from 4.1 to 5.1% with the onset of the two-way shape memory effect, and the temperature ranges of forward and reverse martensitic transformation reduce to 1–2 K. It is shown for the first time that as a result of stress-induced martensite aging for 3 h under stress |σ| = 590 MPa the critical stresses of the martensite formation σ_Ms decreases by a factor of 2.5 and stress hysteresis ∆σ decreases by a factor of 1.4 under superelasticity conditions compared to the initial crystals. This contributes to a higher efficiency and cyclic stability of the elastocaloric effect with adiabatic cooling ∆T_ad = 5.0 ± 0.5 K in [001]_L21-oriented Ni₄₉Fe₁₈Ga₂₇Co₆ single crystals after stress-induced martensite aging for 3 h. [ABSTRACT FROM AUTHOR]