Healing effect of electric current treatment on superelasticity and elastocaloric effect of TiNi shape memory wire

Abstract

This study investigated the healing effects of electric current treatment on Ni-rich TiNi shape memory wire after every 100 superelastic cycles. The diameter of the TiNi wire was 0.5 mm. The electric current treatment was applied without removing the wire from the tensile machine, aiming for online healing of the shape memory alloy. The electric current treatment showed an obvious healing effect, which restored the superelastic and elastocaloric properties of the functionally degraded TiNi shape memory wire. With treatment conditions of 20.4 A/mm2 and 2 min (the temperature of the wire increased up to 280 °C in 10 s), the elastocaloric temperature rise and drop of the TiNi wire recovered about 14% and 6% after 3–4 treatments, respectively, as compared with the case without any heat treatment. TEM observations indicated that the residual martensite introduced into the TiNi wire during superelastic cycles could be eliminated through the electric current treatment. Experimental results demonstrated that electric current treatment was a promising method to restore the functionality of the TiNi SMA wire after several superelastic cycles without the need to remove the wire from the apparatus, which would thus improve the performance of shape memory alloys during their long-term application.