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 coeffi-cients of the linear thermal expansion) have been thereby found in the two phase temperature range: it means sample shorting during the forward transformation and sample lengthening during the reverse transformation and visa versa as well as the both cases during both direct and reverse trans-formations.
The spontaneous sample deformation during the stress-free martensitic transfor-mation differs in different SMA from each other up to one order of magnitude, but lays in all cases in elastic deformation region.
The dilatation effects will be consider 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 sponta-neous deformation to the martensitic deformation experimental measured by stress-induced transformation is introduced. Its values were calculated for all investigated SMA-samples and lay 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 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.