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Viktor Prieb, "MRS-Office Dr. Prieb" at the TU-Berlin, Berlin, Germany, 2009 in the cooperation with Andreas Zilly and Norbert Jost, "Materials Development and Test Laboratory" of the University Pforzheim, Pforzheim, Germany Abstract: Three kind of shape memory-alloys (SMA?s) - single crystals Cu-Al-X (X=Zn, Mn, Ni), and MnCu as well as TiNi-polycristals - have been investigated dilatometrically in the temperature interval of martensitic transformations. Three kind of length change (or coefficients of the linear thermal expansion) have been thereby found in the two phase temperature range: sample shorting during the direct transformation and sample lengthening during the reverse transformation or visa versa, as well as the both cases during both direct and reverse transformations. The spontaneous sample deformation during the stress-free martensitic transformation differs in different SMA from each other up to one order of magnitude, but suits in all cases in elastic deformation region. The dilatation effects are considered as a result of a non-complete accommodation of the martensitic lattice deformation under the elasticity limit (yield) by various accommodation mechanisms. On that basis an accommodation degree as a relation of the measured spontaneous deformation to the martensitic deformation experimental measured by stress-induced transformation is introduced. Its values were calculated for all investigated SMA-samples: they lie in an interval from 75% up to 99%. The thermal expansion of SMA in the temperature interval of martensitic transformations is analysed and discussed on the basis of physical, thermodynamical and crystallographical aspects of martensitic transformations in SMA?s. The width extension of the thermal hysteresis loops depending on the scanning rate is also investigated dilatometrically, and a physical limiting of the work-frequency of SMA-actuators is proved and discussed. More: Article (full script with pictures, english) as PDF-file Home |