Discovered in 1959, Nitinol is a functional metal material with shape memory properties and superelasticity. Shape memory springs have been used in industrial and automotive applications, and superelasticity has been used in products such as orthodontic wires, underwire for women's underwear, and mobile phone antennas, which are recognized for their ability to return to their original shape after bending. Each of these uses creates a huge market demand.
In the past 20 years, a variety of medical devices that can be put into the human body due to superelasticity have been born, promoting the development of minimally invasive treatments and saving more human lives.
Superelasticity makes it softer than stainless steel, stiffer than polymers, flexible when bending, resilient after high strains, and able to transmit sufficient torque in complex paths. Nitinol's unique ability to slide into the body without damaging blood vessels or organs is essential for use in medical guides, stents and heart valve holders.
Effect of heat treatment parameters on optimized performance of nickel-rich nickel-titanium wires (NiTi/ Nitinol), which are intended for use as actuators in various industries. In this case, the maximum recovery strain and actuating Angle that can be achieved by the nitinos wire are used as indicators of the best performance. The heat treatment was carried out at different temperatures of 400~500℃ and time of 30~120 min, and the influence of heat treatment parameters on the driving performance and properties of the nickel-titanium nor-wire was studied. The evaluation covers changes in density, hardness, phase transition temperature, microstructure and alloy composition resulting from these heat treatments. DSC analysis showed that the austenite transition temperature decreased from 42.8℃ to 24.39℃ as the heat treatment temperature increased from 400℃ to 500℃, which was attributed to the formation of Ni4Ti3 precipitates. The austenite transition temperature increases with the increase of heat treatment time. It was found that the hardness of heat treated samples was negatively correlated with the heat treated temperature. This trend can be attributed to the formation and growth of Ni4Ti3 precipitates, which affect the matrix properties. A novel method involving image analysis is used as a simple and powerful analytical method for measuring the recovery strain of wires when driven. The study found that the heat treatment temperature was increased from 400℃ to 500℃ for more than 30 minutes, and the recovery strain was increased from 0.001 to 0.01, thus maximizing the shape memory effect.
