Effect of Heat Treatment Temperature and Heat Treatment Time on Properties and use of NiTi Shape Memory Implant Material

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 Xray Spectroscopy (EDS) and mechanical tests.Results show that Ni 4 Ti 3 phase was formed as a result of heat treatment. Heat treatment time and temperature affected amount, distribution and shapes of NiTi and Ni 4 Ti 3 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.