Stress-induced martensite aging accompanied ω-phase precipitation in NiFeGaCo single crystals

The effect of ω-phase particles precipitated prior to or during stress-induced martensite aging (SIM-aging) on the two-way shape memory effect (TWSME), reversible strain, thermal hysteresis and martensite formation temperature has been established in Ni_47.5Fe₁₅Ga_27.5Co₁₀ single crystals. The experiment was conducted on single-phase quenched single crystals. In contrast, SIM-aging was accompanied by the precipitation of ω-phase particles in oriented L1₀-martensite, and on heterophase single crystals, where ω-phase was previously precipitated in unloaded L2₁-austenite, whereas SIM-aging was not accompanied by particle precipitation. The TWSME characterized by optimal parameters: a high reversible strain of up to 4%, narrow thermal hysteresis (15−30 K), and high temperatures (up to 417 K) obtained in heterophase Ni_47.5Fe₁₅Ga_27.5Co₁₀ single crystals, in which ω-phase particles precipitated before SIM-aging in the austenitic L2₁-phase, compared with quenched single crystals, where nanoscale ω-phase particles precipitated in the oriented L1₀-martensite during SIM-aging.