Investigation On Two-way Shape Memory Effect And Driving Characteristics Of Shape Memory Alloys

Shape memory alloys (SMAs) have received considerable research and widely use for its superelsticity and shape memory effect, especially the two-way shape memory effect, which makes the SMAs be a promising material using as micro-sensors and micro-actuators. However, the TWSME is not a natural behavior of SMAs, suitable thermo-mechanical training is required to develop this effect. And the mechanism of TWSME is still unknown. In this article, a new method of developing TWSME is designed for SMAs. The effects of heat treatment and thermo-mechanical training on the TWSME of TiNi-based were studied. And the mechanism of TWSME was also discussed. To the author's knowledge, these research results in this article have not been reported. (1)A TWSME extension spring, which can extend upon heating and contract upon cooling was obtained using constrained annealing and thermo-mechanical training, the elongation can reach 60%. (2)The optimum heat treatment is 550℃ × 1 h/AC and 500℃×1h/AC for TiNi and TiNiCu alloy, respectively. Higher and lower annealing temperature will depress the TWSME. (3) The R-phase transformation also showed TWSME, the recovery rate can reach 25%. (4)The effect of thermo-mechanical training temperature on the TWSME showed that: When the springs were trained in pure martensite, there is an increase of the recovery rate to a saturated value. As the springs were trained in pure austensite and martensite+austensite, there is an increase of the recovery rate to a maximum value and decreased with ongoing training after having passed the maximum value and the maximum TWSME recovery rate is less than that of the SMAs trained in pure martensite. (5)When the TWSME spring is driven by alternative current the time response continually decreased with increasing current very quickly at first stage then slowed down. The maximum elongation increased with increasing current first and then decreased. The best current density is 8.9-10.2A/mm2. (6)There is a decrease of the TWSME recovery rate with working cycles. After 1000 working cycles by thenno-driving or 500 cycles by electrical-thermo-driving, the recovery rate still maintain at 40%.