Large and reversible elastocaloric effect induced by low stress in a Ga-doped Ni-Mn-Ti alloy

• To report a large 22 Jkg -1 K −1 , with reversibility up to 90 % induced by a low compressive 160 MPa stress. • To show the characterization of the elastocaloric performance of the Ni 50 Mn 32 Ti 16 Ga 2 alloy compared with similar Ni-Mn-Ti alloys based on the strength of the elastocaloric effect (|ΔS ISO |/|Δσ|). • To present a non-reported addition of low Ga content in the Ni-Mn-Ti alloy to produce quaternary non-stoichiometry Heusler alloys with favorable elastocaloric properties. The Solid-state cooling based on caloric effects is considered a potential alternative to conventional refrigeration technology, which uses ozone-depleting gases. Several shape memory alloys have attracted attention for solid-state cooling since they present a high reversibility of the caloric effect, which depends mainly on thermal hysteresis and sensitivity to the applied field. In the present work, a study substitution of Mn by Ga in the Ni 50 Mn 34 Ti 16 alloy led to diminished thermal hysteresis in the martensitic transformation by 6 K. The elastocaloric effect, thermal and microstructure properties of a polycrystalline Ni 50 Mn 32 Ti 16 Ga 2 alloy have been characterized. The elastocaloric effect was obtained indirectly from the length change as a function of temperature at constant stress. An isothermal entropy change (ΔS ISO ) of 23.0 J kg −1 K −1 during heating and 22.0 J kg −1 K −1 during cooling was observed for applied stress of 160 MPa. In addition, the ΔS ISO is reversible for a temperature span between 287 and 319 K, reaching a maximum of 20.5 J kg −1 K −1 at 299 K. The thermal hysteresis changed slightly while the applied stress increased up to 160 MPa since the sensitivity of the martensitic transformation temperatures to stress was 0.150 K M/MPa during cooling and 0.160 K/MPa during heating. The X-ray diffraction analysis revealed a mixture of B2-type cubic austenite, 5 M modulated martensite, and a second intermetallic phase identified as Ni 3 Ti. All these results were obtained around room temperature.