High superelasticity NiTi fabricated by cold metal transfer based wire arc additive manufacturing

NiTi alloy exhibits superior superelastic properties but its wide application is limited by its poor workability. In this study, Ni-rich NiTi wire was used as the feedstock and a wall-shaped NiTi component with height of 130 mm was deposited on Ti substrate by cold metal transfer (CMT) based wire arc additive manufacturing (WAAM) process. The microstructure and mechanical properties of the as-deposited NiTi alloy specimens in the horizontal and vertical directions, as well as their correlations were discussed in detail. In particular, the superelastic properties of the deposited materials were evaluated by cyclic loading-unloading tensile test. It was found that a very high superelastic recovery rate of more than 90% can be reached after 25 cycles for samples tested along both the horizontal and vertical directions. The mechanism that governs the high superelasticity in the alloy was explored in terms of microstructure, chemical composition and phase transformation analyses.