Shape Memory Alloys—Industrial Needs and Trend

Shape memory alloy (SMA) exhibits two very unique properties, known as shape memory effect (SME) and superelasticity(SE), both are closely related to thermoelastic martensitic transformation. In SME, when SMA is deformed in martensitic state, it recovers the original shape by heating above Af temperature, where the austenite phase is stable. In SE, when the load is applied to SMA in the austenitic state, the strain is produced by stress-induced martensitic transformation and it vanishes by the reverse transformation on unloading.<br/>Most widely used SMA is TiNi. They are used widely in various areas of applications, such as, medical devices, aerospace, micro-actuators, constructions, etc. There is also an increasing interest in the elastocaloric effect of the alloy.<br/>However, the TiNi has several drawbacks, such as, 1) shape recovery temperature (Af temperature) is limited to about 100 degC. 2) Poor plastic formability. 3) functional/structural fatigue, etc. To overcome these drawbacks, extensive effort has been made to develop new alloys, new processing method, and to gain further insight into the transformation mechanism.<br/>This talk will review the recent trend in SMA research and introduce some of the emerging applications.