The influence of heat treatment on the thermomechanical response of Ni-rich NiTi alloys manufactured by selective laser melting

This study presents the effects of solution annealing and subsequent aging on shape memory response of Ni-rich Ni50.8Ti49.2 alloys fabricated by Selective Laser Melting. After solutionizing, samples were heat treated at selected times at 350 °C and 450 °C and their shape memory effect, superelasticity, and transformation temperatures were determined. It was found that transformation temperatures, transformation behavior, strength, and recoverable strain are highly heat treatment dependent. Samples aged at 350 °C showed better recovery in superelasticity tests where 350 °C-18 h aged samples exhibited almost perfect superelasticity with 95% recovery ratio with 5.5% strain in the first cycle and stabilized superelasticity with a recoverable strain of 4.2% after 10th cycle. Meanwhile, 450 °C-10 h aged sample exhibited 68% recovery with a recoverable strain of 4.2% in the first cycle and stabilized recoverable strain of 3.8% after 10th cycle.