Review on the temperature memory effect in shape memory alloys

Abstract

Shape memory alloys (SMAs) are well known for their unique shape memory effect (SME) and superelasticity (SE) behavior. The SME and SE have been extensively investigated in past decades due to their potential use in many applications, especially for smart materials. The unique effects of the SME and SE originate from martensitic transformation and its reverse transformation. Apart from the SME and SE, SMAs also exhibit a unique property of memorizing the point of interruption of martensite to parent phase transformation. If a reverse transformation of a SMA is arrested at a temperature between reverse transformation start temperature (A _s) and reverse transformation finish temperature (A _f), a kinetic stop will appear in the next complete transformation cycle. The kinetic stop temperature is a ‘memory’ of the previous arrested temperature. This unique phenomenon in SMAs is called temperature memory effect (TME). The TME can be wiped out by heating the SMAs to a temperature higher than A _f. The TME is a specific characteristic of the SMAs, which can be observed in TiNi-based and Cu-based alloys. TME can also occur in the R-phase transformation. However, the TME in the R-phase transformation is much weaker than that in the martensite to parent transformation. The decrease of elastic energy after incomplete cycle on heating procedure and the motion of domain walls have significant contributions to the TME. In this paper, the TME in the TiNi-based and Cu-based alloys including wires, slabs and films is characterized by electronic-resistance, elongation and DSC methods. The mechanism of the TME is discussed.