Temperature Memory Effect Research Articles

Thermodynamic study of the temperature memory effects in Cu–Al–Ni shape memory alloys

This work presents careful adiabatic calorimetry measurements of the temperature memory effects on a Cu–Al–Ni shape memory alloy single crystal. These effects, which appear after partial martensitic transformations, have been systematically studied. The subsequent delay of the transformation as a function of the thermal history is described by means of a straightforward model, which makes full use of the phase transformation thermodynamic functions, carefully determined from the specific heat results. This model predicts on quantitative grounds, the decrease in the transformed mass in the successive thermal cycles. It also provides information about the distribution of the elastic energy among the martensitic plates in the low temperature phase, which is a characteristic feature of these alloys. The knowledge of the elastic states is not only required to analyze the properties of the martensitic phase but also to describe the kinetics of any physical quantity in the reverse transformation.

The temperature memory effect and the influence of thermo-mechanical cycling in shapememory alloys

Apart from the well-known shape memory effect (SME), the temperature memoryeffect (TME), i.e., the ability of a material to remember the heating interruptedtemperature in the previous thermal cycle, is another interesting phenomenon observed inmany shape memory alloys (SMAs). In this paper, based on previous and currentexperimental observations, we propose a phenomenological model to reproduce theTME. Subsequently, we study the influence of thermo-mechanical cycling (uniaxialtension) on the TME in a polycrystalline NiTi SMA wire (0.51 mm diameter).The maximum tensile strain in each cycle is 10%, which is beyond its elasticlimit. The evolution of the peak transition temperature in the forward and reversetransformations and the TME upon thermo-mechanical cycling is investigated bydifferential scanning calorimetry. It is proved that the TME is a stable intrinsicphenomenon and can be utilized even under severe thermo-mechanical conditions.

Wide Range Temperature Memory Effect of an In Situ NiTi Alloys Composite

Incomplete martensitic transformation characteristics of NiTi shape memory alloys after cold deformation were studied. By designing the shape of the original surface curve, macroscopic domains with different dislocation density were introduced into the NiTi alloys and materials possessing the characteristics of composites were obtained. Due to the interactions between the dislocation texture and martensite variants, the reverse transformation temperatures were found to expand over a large temperature window, which gives temperature memory effect a higher potential for application.

Mechanisms of the multi-shape memory effect and temperature memory effect in shape memory polymers

As recently demonstrated, after programming, thermo-responsive shape memorypolymers can exhibit the multi-shape memory effect (SME) upon heating. In addition, it is confirmed that the temperature corresponding to the maximum recovery stress in constrained recovery is roughly the temperature at which pre-deformation is conducted, a phenomenon known as the temperature memory effect (TME). In this paper, we propose a framework to investigate the underlying mechanisms behind both effects and provide the conditions for the TME. According to this framework, we can achieve fully controllable shape recovery following a very complicated sequence in a continuous manner.

Effects of Thermal Cycling on the Temperature Memory Effect of TiNiNb Alloy

The temperature memory effect (TME) of a Ti48Ni17Nb35 alloy consisting of B2-TiNi(Nb) and bcc-NbTi with Ti2Ni precipitation was investigated by using differential scanning calorimetry (DSC). Results showed that the TME of the alloy persisted on the second global DSC heating curve. This repeatable TME persisted even after 30 complete thermal cycles from below M f to above A f. With a further 30 incomplete thermal cycles upon heating up to a specific arrested temperature, the TME was enhanced and persisted in the next 32 complete testing cycles. This is different from the previous understanding that TME was a one-time phenomenon.

Kinetic effects in the mixed β to [formula omitted] martensitic transformation in a Cu–Al–Ni shape memory alloy

A single crystal with a selected composition of a Cu–Al–Ni shape memory alloy, undergoing two martensitic phase transformations when cooling from the common parent phase, β 3 → β 3 ′ + γ 3 ′ , has been studied by adiabatic calorimetry. As the coexistence of two different martensites has a strong influence on the transformation kinetics, both the forward and the reverse phase martensitic transformation have been carefully studied by means of very low thermal rate dynamic thermograms. Temperature memory effects have been observed in the β 3 ′ transformation but not in the γ 3 ′ one. Finally, radiation-cooling procedures were used to study the forward transformation and showed the interaction between the two types of martensite variants on the nucleation processes. This last technique was found useful to evaluate the latent heat released at each individual nucleation event, throughout the transformation progress. The consequent sample self-heating alters this process, which dramatically affects the β 3 ′ / γ 3 ′ ratio and the final martensitic state.

The influence of partial cycling on the martensitic transformation kinetics in shape memory alloys

The martensitic transformation kinetics during partial cycling and the so-called “hammer” effect has been carefully characterized in Cu–Al–Ni shape memory alloys. These temperature memory effects were measured by adiabatic calorimetry and analyzed within the frame of a new thermodynamic model. A straightforward study of the nucleation processes explains on quantitative grounds the shift of the reverse transformation to higher temperatures and the presence of a secondary C p peak associated to these phenomena. The optical observations support the calorimetric results. Finally, the release of the elastic energy in the martensitic state due to the different thermal cycles has been determined.

Effect of heat treatment on the transformation behavior and temperature memory effect in TiNiCu wires

The effect of heat treatment on the phase transformation behavior of TiNiCu shape memory alloy wires and the temperature memory effect in this alloy were investigated by the resistance method. These results showed that with increasing annealing temperature and annealing time, the phase transformation temperatures of TiNiCu wires were shifted to higher temperatures in the heating and cooling process. It was also found that incomplete thermal cycles, upon heating the TiNiCu wires, which were arrested at a temperature between the start and finish temperatures of the reverse martensite transformation, could induce a kinetic stop in the next complete thermal cycle. The kinetic stop temperature was closely related to the previous arrested temperature. This phenomenon was defined as the temperature memory effect. The result of this study was consistent with the previous report on the phenomenon obtained using the differential scanning calorimetry method, indicating that temperature memory effect was a common phenomenon in shape memory alloys.

Repeatable temperature memory effect of TiNi shape memory alloys

An incomplete transformation cycle induces a kinetic stop in the following complete transformation cycle in TiNi shape memory alloys. The kinetic stop can be regarded as a memory of the previous interruption temperature. This memory was generally believed to be a one-time phenomenon. Herein, we show that the temperature memory effect is actually a long-lasting phenomenon. Experimental results show that a repeatable temperature memory effect can be introduced into a TiNi alloy by a deformation lager than 12%. Deformation induced dislocations are considered a main factor to the persistence of the memory. The memory becomes more distinct with increasing numbers of the incomplete thermal cycle, but the memory becomes less distinct with increasing numbers of subsequent complete transformation cycling.

A study on NiTiNbCo shape memory alloy

The influence of Co on the microstructure, phase transformation temperature, mechanical properties and shape memory effect of TiNiNb alloys has been investigated by X-ray diffraction, differential scanning calorimetry, tensile stress–strain measurements and bending tests, respectively. The results show that the addition of Co suppresses the brittle (Ti,Nb) 2Ni phase of NiTiNb alloys, and the phase transformation temperature and lattice parameter of Ni 46.5− x Ti 44.5Nb 9Co x alloys are decreased with the increase of Co content. The yield strength of NiTiNb alloys has been improved due to the addition of Co. In particular, Ni 45.5Ti 44.5Nb 9Co 1 alloy exhibits highest yield strength among the Ni 46.5− x Ti 44.5Nb 9Co x (Co = 0.5, 1, 1.5, 2) alloys, and a maximum completely recoverable strain of 7.8% has been achieved.

A new quantitative approach to the thermoelastic martensitic transformation: The density of elastic states

A thermodynamic study, based on high-sensitivity adiabatic calorimetry, of the martensitic transformation undergone by Cu–Al–Ni shape memory alloys is presented. From the specific heat data, the thermodynamic function values, and in particular the crystal free energy, as functions of temperature, have been obtained. These results have permitted a careful estimation of the phase transformation temperatures of each β 3 ′ martensite plate as a function of its stored elastic energy. Within this frame, the distribution density of the elastic energy states in the martensitic phase is directly derived from the specific heat data. It also permits a simple analysis of the nucleation processes and gives a convincing explanation of the temperature memory effects.

Incomplete martensitic transformations in NiTi thin films

Nickel–titanium thin films were deposited onto silicon substrates and subjected to incomplete martensitic transformations . With wafer curvature methods, we observed a stress discontinuity that seems analogous to the splitting of the endothermic peaks measured by differential scanning calorimetry due to the temperature memory effect. The martensite start temperature ( M s ) remains constant during incomplete forward transformations, resulting in a constant-stress range between the arrest temperature and M s . However, incomplete reverse transformations start immediately at the arrest temperature. X-ray diffraction measurements confirm these path-dependent behaviors, which are consistent with the thermodynamic model of martensitic transformations.

Temperature memory effect in Cu–Al–Ni shape memory alloys studied by adiabatic calorimetry

The temperature memory effect exhibited by Cu–Al–Ni shape memory alloys was studied by means of adiabatic calorimetry and microscopic observations. The harmonic, anharmonic and electronic contributions to the lattice specific heat were estimated by using the experimental data of the metallic components. The obtained results provide an accurate baseline for the quantitative study of the martensitic phase transformations as a function of the thermal history in these alloys. The specific heat of a Cu–Al–Ni sample was measured from 140 to 350 K throughout the phase transition region, and the temperature memory effect was carefully studied. These results are in good agreement with the optical observations as a function of temperature. The global behaviour of the martensitic transformation as regards the temperature memory effect is discussed and interpreted in terms of the microscopic mechanisms of nucleation and motion of the martensite plates.

Phase transformation and microstructure of Ni–Mn–Ga ferromagnetic shape memory alloy particles

In the present paper, ball milling is used to produce Ni49.8Mn28.5Ga21.7 particles of micrometer size. Although the characteristics of transformation are not observed in the as-milled particles from 150 to 523 K from differential scanning calorimetry (DSC) study, the particles exhibit the same transformation behaviour as the bulk sample after annealing at 1073 K for 2 h. The as-annealed particles show good thermal cycling stability even after five thermal cycles. Temperature memory effect during the reverse martensitic transformation is found in the as-annealed particles. The particles exhibit regular shape, with 10M martensite structure at room temperature.

Aging, rejuvenation, and memory effects in the domain state of Sr0.75Ba0.25Nb2O6

The dielectric susceptibility of strontium–barium niobate, Sr0.75Ba0.25Nb2 O 6, reveals strong hole-like aging behaviour in its ferroelectric state. The isothermal evolution of the linear susceptibility satisfactorily follows a stretched exponential law. After aging the sample at a selected temperature both rejuvenation and memory effects are observed in temperature cycle experiments. They seem to indicate cluster glass-like properties of the domain state involved.

Effect of Alloying Additions on the SFE, Neel Temperature and Shape Memory Effect in Fe-Mn-Si-based Alloys

A range of Fe–Mn–Si-based shape memory alloys has been investigated to examine the interplay of composition, stacking fault probability (SFP) and Neél temperature on the shape memory effect (SME). It has been found that the SFP (inversely proportional to stacking fault energy) showed little correlation to the SME for the range of alloy compositions examined. Further, the Neél temperature was not found to exhibit a significant effect on the SME. The addition of interstitial elements, however, was found to markedly decrease the SME.

Reply to comments on ‘Incomplete transformation induced multiple-step transformation in TiNi shape memory alloys’

The discussion is focused on clarifying whether there is temperature memory effect (TME) in the R-phase to parent phase transformation in TiNi shape memory alloys. The authors prove that the TME dose occurs. However, the TME in this transformation is much weaker than that in the martensite to parent transformation. In some cases, it needs many repetitions to observe TME in this transformation. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Martensitic transformations and thermal expansion behaviors of structural heterogeneous NiTi alloys

Martensitic transformation characteristics of NiTi shape memory alloys after severe cold deformation were studied. By designing the shape of the original surface curve, distinct macroscopic domains with different dislocation densities were introduced into the NiTi alloys, and materials possessing the characteristics of composites were obtained. Due to the interactions between the deformation structure and martensite variants, the reverse transformation temperature range was significantly enlarged. One of the possible applications for these materials is the so-called temperature memory effect in a wide temperature range.

Comments on “Incomplete transformation induced multiple-step transformation in TiNi shape memory alloys” [Scripta Mater 2005;53:335

A recent investigation [Scripta Mater 2005;53:335] concluded that there is no temperature memory effect (TME) in the R-phase to austenite phase transformation in NiTi shape memory alloys (SMAs). That was different from previous findings for a NiTiFe SMA. We show that TME does occur in a NiTi SMA, but that the significance in the NiTi tested is much less compared with that reported in NiTiFe. We also found that, in this NiTi, the applied heating rate has a great influence on the appearance of the TME, and that the TME is only observable in the middle range of the transformation.

Temperature memory effect in CuAlNi single crystalline and CuZnAl polycrystalline shape memory alloys

Temperature memory effect (TME) induced by incomplete cycling in CuAlNi single crystalline and CuZnAl polycrystalline shape memory alloys were investigated by differential scanning calorimeter. Results showed that the TME is a common phenomenon in shape memory alloys, caused by a partial martensite to parent phase transformation.