Elastocaloric effect in heterophase TiNi single crystals

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 [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 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

Elastocaloric effect in aged single crystals of Ni54Fe19Ga27 ferromagnetic shape memory alloy

In the present study, the effect of 0-phase dispersed particles on both the L21(B2)-10M/14ML10 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 0-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 DTSE = 270 K as compared with the initial as-grown crystals (DTSE = 197 K). The adiabatic cooling values DTad are similar for the as-grown crystals DTad = 10.9 (0.5) K and crystals aged at 773 K DTad = 11.1 (0.5) K. The crystals containing temperature range of DTSE = 255 K with slightly smaller adiabatic cooling DTad 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.В ст. ошибочно: Nikita S. Suriko

The elastocaloric effect in [001]-single crystals of titanium nickelide containing nanosized Ti3Ni4 particles

The temperature dependence of the elastocaloric effect is studied and the experimental values of the adiabatic temperature change, ΔTad, in the loading/unloading cycles of up to 13.3 K and 16.4 K in quenched and aged Ni50.6Ti49.4 single crystals at 573 K, 1 h, respectively, are obtained. In aged crystals, a specific feature of the elastocaloric effect temperature dependence (an increase in ΔTad above the temperature TR = 273 K) is found, which is due to a change in the sequence of stress-induced martensitic transformation from R–B19' to B2–B19'. The factors (the dissipated energy in the working cycle and the strain hardening coefficient during the stressinduced martensitic transformation) affecting the elastocaloric effect are discussed. It is shown that the aged single crystals have a high coefficient of performance (COP of up to 31), which is promising for the solid-state cooling technologies

The Effect of Thermal Treatment on Microstructure and Thermal-Induced Martensitic Transformations in Ni₄₄Fe₁₉Ga₂₇Co₁₀ Single Crystals

Heat treatments of single crystals of Ni44Fe19Ga27Co10 (at.%) shape memory alloys cause various microstructures of the high-temperature phase. The nanodomain structure, consisting of regions of the L21- and B2-phases, and nanosized particles are the main parameters that change during heat treatments and determine the mechanism of nucleation and growth of martensite crystals, the size of thermal-induced martensite lamellae, the temperature Ms, and the temperature intervals of the martensitic transformation. In the as-grown single crystals, the high-temperature phase has only the L21-structure and the MT occurs at low (Ms = 125 K) temperatures due to the motion of the practically single interphase boundary in narrow temperature ranges of 3–7 K. The reduction in the volume fraction of the L21-phase to 40% and the formation of nanodomains (20–50 nm) of the L21-and B2-phases due to annealing at 1448 K for 1 h with quenching causes an increase in the MT temperatures by 80 K. The MT occurs in wide temperature ranges of 40–45 K because of multiple nucleation of individual large (300–500 µm) martensite lamellae and their growth. After aging at 773 K for 1 h, the precipitation of nanosized particles of the ω-phase in such a structure additionally increases the MT temperatures by 45 K. The MT occurs due to the multiple nucleation of packets of small (20–50 μm) martensite lamellae

Superelasticity and elastocaloric cooling capacity in stress-induced martensite aged [001]А-oriented Ni54Fe19Ga27 single crystals

The research paper presents a study of the effect of stress-induced martensite aging along the [001]A-deformation axis of the sample on both elastocaloric cooling capacity and superelasticity in Ni54Fe19Ga27 single crystals in compression. It has been experimentally shown that L10-martensite stabilization after the stress-induced martensite aging enhances the superelasticity parameters for the elastocaloric performance in the studied single crystals. In the stress-induced martensite aged Ni54Fe19Ga27 single crystals, the stress level of martensite formation σMs and stress hysteresis Δσ decrease by 130 MPa and by 16–17 MPa, respectively, compared with the as-grown crystals. Therefore, the stress-induced martensite aging increases the material efficiency for solid-state cooling systems: specific adiabatic temperature change per unit stress ΔTad/σMs increases by 4.4 times (ΔTad/σMs = 291.9 K/GPa (at Т = 348 K)) and coefficient of performance reaches COP = 24.5 in stress-induced martensite aged crystals as compared with the as-grown crystals (ΔTad/σMs = 62.4 K/GPa (at Т = 348 K), COP = 21.7). Smaller stress hysteresis corresponds to less energy dissipation in an operating cycle, which is also certainly useful for optimizing elastocaloric properties of a material. Moreover, both as-grown and stress-induced martensite aged crystals demonstrate high cyclic stability during loading/unloading cycles and weak temperature dependence of the elastocaloric cooling capacity ΔТad = 10.3–11.0 K in a wide operating temperature range up to 145–197 K. Thus, stress-induced martensite aged Ni54Fe19Ga27 single crystals oriented along the [001]А- direction are expected to be promising materials for elastocaloric application

Cyclic stability of superelasticity in [001]‑oriented quenched Ni44Fe19Ga27Co10 and Ni39Fe19Ga27Co15 single crystals

The study of the influence of the cobalt content on the cyclic stability of superelasticity (SE) was carried out in quenched Ni44Fe19Ga27Co10 and Ni39Fe19Ga27Co15 (at.%) single crystals under compression. It is shown that an increase in the cobalt content leads to embrittlement of the material and a decrease in the cyclic stability of SE. In Ni44Fe19Ga27Co10 single crystals, during the first 20 loading/unloading cycles, the elastic energy relaxation occurs along with the formation of dislocations and residual martensite, which leads to a decrease in critical stress of martensite formation and in stress hysteresis. During the next 80 cycles, SE becomes more stable. Stabilization is accompanied by a slight change in the parameters. On the contrary, Ni39Fe19Ga27Co15 single crystals are characterized by high-strength characteristics, which lead to high SE stability during the first 20 loading/unloading cycles. However, after 20 cycles, a strong degradation of the SE is observed through the formation of microcracks, which ultimately leads to the destruction of the sample. The results of work are replicable for cycling at different temperatures from all temperature ranges of superelasticity