Pulsed electric current annealing of (Ni,Cu)-rich Ti49Ni41Cu10 shape memory wire for superior superelasticity and stable elastocaloric cooling effect

This study designed a (Ni,Cu)-rich Ti ₄₉Ni ₄₁Cu ₁₀ shape memory wire annealed by pulsed electric treatment of 60 A/mm ² for 0.3 sec. Granular and strip-type Ti(Ni,Cu) ₂ precipitates, formed before application of the electric current treatment, facilitated the plastic deformation during the wire drawing process. The wire demonstrated stability in superelasticity and elastocaloric cooling capability. The accumulated residual strain was only 0.15 % after 50 superelastic cycles with an applied strain of 3.5 % at 338 K. The elastocaloric temperature drop of the wire remained at about 9.4 K for 50 cycles. Moreover, under 3 % applied strain, the wire exhibited elastocaloric temperature drops of 5.3 K to 8.1 K within the application window of 323 K to 373 K. TEM observations confirmed that the grain size of the wire was about 20–30 nm, which led to the homogeneous superelasticity performance. Furthermore, the superior compatibility between the B2 and B19 phases reduced plastic deformation at the interfaces during martensitic transformation. The stable functionality and elastocaloric cooling capacity of the wire originated from the combination of nanocrystalline structure and superior compatibility between the B2 and B19 phases. These results demonstrated that the Ti ₄₉Ni ₄₁Cu ₁₀ SMA wire could be fabricated due to the presence of ductile Ti(Ni,Cu) ₂ precipitates, and the subsequent pulsed electric current treatment caused rapid annealing to achieve a stable functional performance.