In the present study, the effect of γ′-phase dispersed particles on both the L2₁(B2)-10M/14M-L1₀ martensitic transformations and the elastocaloric effect in aged Ni₅₄Fe₁₉Ga₂₇ single crystals oriented along the [001]-direction was investigated. It was experimentally shown that aging strongly affects the elastocaloric properties of these crystals. The precipitation of semi-coherent γ′-phase particles up to 500 nm in size in the crystals aged at 773 K for 1 h leads to a 1.4 times increase in the operating temperature range of the elastocaloric effect up to ΔT_SE = 270 K as compared with the initial as-grown crystals (ΔT_SE = 197 K). The adiabatic cooling values ΔT_ad are similar for the as-grown crystals ΔT_ad = 10.9 (±0.5) K and crystals aged at 773 K ΔT_ad = 11.1 (±0.5) K. The crystals containing incoherent γ′-phase particles sized 5–35 μm (after aging at 1373 K for 0.5 h) possess an operating temperature range of ΔT_SE = 255 K with slightly smaller adiabatic cooling ΔT_ad below 9.7 (±0.5) K. The aged [001]-oriented Ni₅₄Fe₁₉Ga₂₇ single crystals demonstrate high cyclic stability: the number of cycles does not influence the adiabatic cooling values and parameters of loading/unloading curves regardless of the particle size. The ways to improve the elastocaloric cooling parameters and stability of the elastocaloric effect by means of dispersed particles in the NiFeGa ferromagnetic shape memory alloy were discussed.

The present study investigates the high-temperature shape memory effect (SME) in heterophase Ni _50.3 Ti _32.2 Hf _17.5 polycrystals with nanosized H -phase particles after stress-induced martensite (SIM) aging in tension and compression. SIM aging created the conditions for fully reversible two-way SME with a strain of up to 50% of the one-way shape memory strain. SIM aging altered the viscoelastic properties of material, in particular, the elastic moduli of austenite and martensite increased, as did internal friction. Increased interface mobility is suggested as the reason for internal friction growth.