The paper presents studies of the elastocaloric effect during the stress-induced B2–(R)–B19′ martensitic transformation depending on the microstructure and test temperature in Ni50.6Ti49.4 and Ni50.8Ti49.2 (at.) single crystals oriented along the 001B2 direction. The aging of TiNi single crystals at 573 and 823 K for 1–1.5 h improves the characteristics of superelasticity and elastocaloric effect. Precipitating large Ti3Ni4 particles with the size of ~ 400 nm aged at 823 K leads to an increase in the temperature range of elastocaloric effect and in the maximum adiabatic cooling ΔTad up to 24.2–25.3 K compared with quenched single crystals (ΔTad = 14.3 K). TiNi single crystals containing nanosized Ti3Ni4 particles smaller than 10 nm (aging at 573 K) have a distinguishing feature: two-stage reverse B19′–R–B2 martensitic transformation leads to staging on the elastocaloric effect temperature dependence. The maximum ΔTad in these single crystals is lower compared with single crystals aged at 823 K. It is equal to 16.8 K and 21.3 K in Ni50.6Ti49.4 and Ni50.8Ti49.2 alloys, respectively. However they demonstrate record coefficient of performance up to 27.8 in the Ni50.6Ti49.4, which characterizes them as promising for further use in solid-state cooling devices.
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