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by the intrinsic transformation velocity V. Prieb, V. Wolff "MFS-Büro Dr. Prieb" Report on the Int. Conf. "Readings on the materials with shape-memory and superelasticity effects, 24.-25. Mai 2000, Kiew", Kiew, 2000. The calorimetric measurements of transformation temperature intervals at different scanning rate on Ti0.5Ni0.5 (B2-B191), Ti0.5Ni0.5-x(Au,Pd,Pt)x (B2-B19), Ti0.5Ni0.482Alx0.018 (B2-R-B191), Mn0.84Cu0.16 (fcc-fct) poly-crystals and (Cu-Al)-based (B2-9R) single crystals memory alloys are shown for all alloys the increasing of the transformation intervals by increasing both of the hysteresis width and the slope of hysteresis loops at the increasing of the scanning rate. The transformation frequency becomes approximately constant value about 0.01Hz if the scanning rate is greater as about 1K/s. The measured velocity of the single phase boundary (the soliton velocity) at the transformation of a Cu-Al-Zn single crystal at a constant load is about 10-5m/s at the indifferent phase equilibrium and about 10-3m/s at the strong not equilibrium conditions (shock induced transformation). Introduction: Shape memory alloys (SMA) are recognized as intelligent materials because they are capable to feel a change in external parameters (temperature, mechanical stress etc.) and to act (shape or recovery force change etc.) according to this change by change of their internal parameters (lattice parameters, internal energy etc.). These properties are the best conditions for their application as actuators. In the series of concurrent materials as ferromagnetic or ferroelectric ones, SMA have much greater strain and stress response, but much slower response time or the action frequency. The response time of SMA actuators is a sum of cooling and heating time through the characteristically temperature interval Mf-Af within that take place forward and reverse martensitic transformations that causes the action. The frequency of SMA actuator is a number of complete transformation cycles per 1 sec. This frequency is less as 1Hz. Intensive investigations of the last time focus on the increasing this frequency by means of the miniaturization of SMA actuators and of the using of more effective cooling methods, for example, by means of the thermoelectric Peltier effect. On this way the frequency about 10 Hz is reached. Actuating frequencies up to 100 Hz are theoretical predicted by miniaturization of SMA actuators (SMA foils down to 1-2 µm) and conventional cooling methods. It will be discussed an alternative way to increase of action frequency of SMA actuators in which the martensitic transformation could be induced by electric or magnet field instead of the thermo-inducing. But there are no optimistic results on this way. The analyze of this investigation trend shows that only the scanning rate, connected with heat transfer, will be accepted as a limiting factor for the action frequency of SMA actuators. The transformation kinetics or a possible physical limiting of the transformation rate will be not discussed and investigated. It is the aim of the present paper to investigate existence of this intrinsic limiting of the response time of SMA actuators. Conclusion: As show the experimental results, it exists an intrinsic transformation rate limit so that the increasing of the external scanning rate do not leads to proportional increasing of the intrinsic velocity of the thermoelastic martensitic transformation, but one to the proportional expansion of the transformation interval because the whole process is limited by the smoother process participant, namely, growth of the martensitic phase, which inertia is causes by own transformation heat and its transfer. More: Article (full script, english) as PDF-file Home |