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.Keywords: temperature memory effect; shape memory alloys IntroductionShape memory alloys (SMAs) have attracted considerable interest as potential candidates for novel engineering and mechanical applications owing to their excellent functional properties, i.e. shape memory effect (SME) and superelasticity (SE) behavior. The unique effects of SME and SE originate from martensitic transformation and its reverse transformation. SMAs also exhibit a unique property of memorizing the point of interruption during transformation from martensite to parent phase. An incomplete thermal cycle upon heating of SMAs (arrested at a temperature T s between austenite transformation start and finish temperatures, A s and A f ) induced a kinetic stop in the next complete thermal cycle. The kinetic stop temperature is closely related to the previous arrested temperature. Therefore, this phenomenon is named the temperature memory effect (TME) [1].

Effects of Composition and Thermal Treatment of Cu-Al-Zn Alloys with Low Content of Al on their Shape-memory Properties

“…It is well known that many copper alloys such as CuAl, Cu-Zn-Al, Cu-Al-Ni and Cu-Al-Mn exhibit shape memory properties [5][6][7] . Cu-based SMAs have attracted much attention due to their good shape memory capacity, narrow temperature region of transformation, ease of fabrication and low production cost 8 . For the alloys of the ternary Cu-Zn-Al system, the shape memory effect is only observed within a certain range of composition which generally contains 16 to 30% of Zn and 4 to 8% of Al 3 .…”

The Influence of Thermal History on the Multistage Transformation of NiTi Shape-Memory Alloys

“…The question arises when a multistage MT is present. Previous works have undoubtedly found the TME in the B19 →R transformation, but it is not so clearly present in the R→Austenite transformation [26]. This seems to be due to the low calorimetric signal of this last transformation.…”

“…It has also been found that after a complete reverse MT, all these effects are erased. In the last few years, various interpretations have been proposed to explain the TME, which seems to be present in most SMAs and related to the relaxation of the elastic strain energy of the martensitic variants [26,28]. In the case of TiNi alloys, some qualitative descriptions have been developed in which the role of the elastic energy, dislocations, and grain boundaries are also discussed [26,29,30].…”

Thermal memory fading by heating to a lower temperature: Experimental data on polycrystalline NiFeGa ribbons and 2D statistical model predictions

“…Fig.7 form [13], on TiNiCu thin films or Fig.2 form [14] on MiMnGa based bulk alloys) may be interpreted as evidence of memory fading by heating to lower temperatures, but have not been given this particular interpretation. …”