Elastocaloric Effect in Heterophase TiNi Single Crystals

• Published in: Shape memory and superelasticity : advances in science and technology 2022-09, Vol.8 (3), p.226-234
• Main Authors: Surikov, N. Yu, Panchenko, E. Yu, Chumlyakov, Yu. I.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Cooling; Crystal structure; Intermetallic compounds; Martensitic transformations; Materials Science; Nickel base alloys; Nickel compounds; Shape memory alloys; Single crystals; Superelasticity; Technical Article; Temperature dependence; Titanium compounds
• ISSN: 2199-384X; 2199-3858
• DOI: 10.1007/s40830-022-00388-9

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 Ni 50.6 Ti 49.4 and Ni 50.8 Ti 49.2 (at.%) single crystals oriented along the [001] B2 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 Ti 3 Ni 4 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 Δ T ad up to 24.2–25.3 K compared with quenched single crystals (Δ T ad  = 14.3 K). TiNi single crystals containing nanosized Ti 3 Ni 4 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 Δ T ad 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 Ni 50.6 Ti 49.4 and Ni 50.8 Ti 49.2 alloys, respectively. However they demonstrate record coefficient of performance up to 27.8 in the Ni 50.6 Ti 49.4 , which characterizes them as promising for further use in solid-state cooling devices.