Shape Memory Effect in Aging of Ni-Ti Shape Memory Alloy Wire Bent in V-Shape at Room Temperature

In this study, Ni-rich Ni-Ti shape-memory alloys (SMAs) were formed at room temperature to reduce the use of expensive dies during the thermomechanical forming and constraint aging process in order to maximize the economic benefits. After undergoing solution treatments at various temperatures, SMA wires were formed at room temperature into different curvatures. Subsequently, the SMA wires were subjected to aging treatments at different temperatures. The springback of SMA wires was examined after forming and after aging. A reverse bending tests were used to explore the shape memory effect (SME) of SMAs. Differential scanning calorimetry (DSC) was employed to measure the phase transformation temperature, and a hardness testing was performed on SMAs as well.

As a result, the phase of all SMAs in this study at room temperature is austenite. The springback decreases with a higher solution treatment temperature or a smaller radius of curvature after forming, while the springback increases with a higher aging temperature after aging. Besides, with an aging temperature of 300ºC, the SMA has the lowest phase transformation temperature and the highest hardness values among the aging temperatures range from 100ºC to 500ºC. Furthermore, all SMAs after aging have a shape recovery rate about 97% in average.