Study Of Temperature Memory Effect Of Shape Memory Alloy

Shape memory alloys (SMAs) have received considerable research and widely use for their shape memory effect and superelsticity. SMAs are promising materials using as many fields with the investigation on their temperature memory effect (TME). However, the TME is obtained by incomplete cycling on heating in SMAs. And so far the mechanism of TME is still unknown. In this article, the TME induced by incomplete mechanical-thermal cycling in TiNi and TiNiCu and CuAlNi single crystalline and CuZnAl polycrystalline SMAs was primary investigated by using the contraction rate-temperature curves of the springs and differential scanning calorimetry (DSC). And the mechanism of TME and the transformation characteristics were also discussed. To the author's knowledge, these reseach results in this article have rarely been reported.(1) The TME was systematically studied using TiNi and TiNiCu springs showing two-way shape memory effect, prepared by heat treatment and thermo-mechanical training, and TiNi and TiNiCu thin films, which were prepared by magnetron co-sputtering,and CuAlNi single crystalline and CuZnAl polycrystalline. Results show the TME is a common phenomenon in shape memory alloy, which is induced by a partial reverse transformation, and a number N of ICHs with different arrested temperatures are performed with decreasing order, N temperatures can be memorized. Results also show TME is enhanced With increasing number of ICHs. (2) Results show the TME is a reversible process, which can be easily wiped out by the following complete thermal cycle. (3) M1 and M2 are two different martensite variants with diverse elastic strain energy and lattice distortions, which transformation to austenite at different temperatures. Thus the mechanism of TME may be both the elastic energy between martensite variants and coherent strain energy between parent phase and martensite. (4) In the TiNi SMAs annealing, the arrested temperature lies between Ms and Rf upon cooling, so only two endothermic peaks occurs in the following heating process corresponding to the transformation of R-phaseâ†'B2 and M2â†'B2. With further decreasing the arrested temperature to a temperature lower than Ms and higher than Mf, three endothermic peaks can be observed in the DSC curve, i.e. M1â†'B2, M2â†'B2 and R-phaseâ†'B2. Results show incomplete transformation upon...