Abstract: The thermal hysteresis of the thermoelastic martensitic transformations monocrystalline Cu-Al-X (X = Zn, Ni, Mn), NiTi, and Mn-Cu and polycrystalline NiTi-X (X = Au, Pt, Pd, Al) shape memory alloys are using calorimetry been investigated. The interior of the hysteresis is all alloys characterized by two internal equilibrium lines which run parallel to each other in the case of the symmetric hysteresis loops. The influence of the crystalline interfaces and the skanning rate on the latent hysteresis and on the thermal coefficient of elasticity is also examined.The relationship between the thermoelasticity and the hysteresis is discussed.
The characteristics of the thermal and ferroelastic hysteresis as, for example, the memory on the reversal points not only during the non complete cycles of the thermo-induced, stress-free martensitic transformations (known as a SMART-effect), but also during the partial cycles of ferroelastic deformation were using calorimetry and tensile--compression-tests of different shape memory alloys were examined. The general behavior of the internal transformation trajectories, which is necessary for the simulation of the hysteresis and the modeling of the shape memory properties is summarized based on the experimental investigations.
Experimental results also show that there exists an internal limitation of the conversion rate, so that the increase of the external Skanierungsrate not proportional increase of the internal rate of conversion leads. The calculated from these data limit of the operating frequency of the shape memory actuators is about 1 Hz