Abstract: In this study, effect of heat treatment parameters, which is applied in order to achieve superelasticity and shape memory, on the nitinol microstructure was investigated. Nitinol is a commonly used material in cardiovascular and orthopedic implant production. Nitinol material used in this study has 50.59% Ni, 0.12% C, 0.0005% Cr, 0.003% Cu, 0.001% Co, 0.012% Fe, 0.1% O, <0.26% H andbalanceTi chemical composition (in at.%).Nitinol wires were heat treated at 540 °C, 550 °C, 560 °C and 570 °C for 10 minutes. Then, heat treatment was applied at 550 °C for 8, 9, 10, 11, 12, 13 and 14 minutes. Heat treated nitinol wires were characterized by optical microscope, Energy-dispersive X-ray Spectroscopy (EDS) and mechanical tests.Results show that Ni₄Ti₃ phase was formed as a result of heat treatment. Heat treatment time and temperature affected amount, distribution and shapes of NiTi and Ni₄Ti₃ phases. Among heat treatment conditions, suitable microstructures were obtained at 540 °C and 550 °C heat treatment temperature and heat treatment times not exceeding 10 minutes. This finding was verified with mechanical tests.

Keywords: Heat Treatment, Nitinol, Shape Memory Alloy, Super elasticity, Medical Device, Ni₄Ti₃.